Steep Workflow Management System

Steep is a Scientific Workflow Management System made for the Cloud

Key features

Distributed

Dynamic and scalable execution of data-driven workflows in a distributed environment such as the Cloud.

Cyclic workflow graphs

Support for cyclic workflow graphs without a priori runtime knowledge. Workflows are converted incrementally and on-demand to so-called process chains.

Capability-based scheduling

Optimized, capability-based process chain scheduling through parallelization and distribution to multiple agents (i.e. Steep instances running in the Cloud or in a cluster).

Automatic failover

Crashed workflows can be resumed without loss of information (even without a database).

Microservice integration

Service metadata allows microservices (also called processing services) with almost arbitrary interfaces to be integrated/executed.

Runtime environments

Built-in runtime environments for executable microservices that are provided as binaries or Docker images.

Plugins

Plugins let you modify generated process chains, the way agents collect results, or add custom runtime environments (e.g. Python, AWS Lambda, Web Processing Services).

Optional databases

If you want your workflows to be persisted in a database over a long period of time, Steep offers support for MongoDB and PostgreSQL.

HTTP and web interfaces

Steep has a REST-like HTTP interface, a web-based user interface for monitoring, and can provide metrics to Prometheus.

Kubernetes

Tight integration with Kubernetes enables optimized resource usage through auto-scaling.

OpenStack

The OpenStack Cloud Connector allows virtual machines hosting additional Steep agents to be created on demand.

Scalability

Its asynchronous event-driven architecture allows Steep to scale horizontally across multiple machines in your cluster and to support complex dynamic workflows with thousands of tasks.

Production-ready

Steep is very reliable and has been used in production for many years to execute workflows from various domains. The source code has a very high test coverage.

Open-Source

Steep is free and open-source. It is released under the Apache License, Version 2.0. The code can be found on GitHub.

Download and get started

Choose from one of the following options to download Steep:

Download Steep 6.2.0 (binaries) Docker image Source code

If you downloaded the binary package of Steep, extract the ZIP file and run the start script:

cd steep-6.2.0
bin/steep

Or, start the Docker image as follows:

docker run --name steep -d --rm -p 8080:8080 \
    -e STEEP_HTTP_HOST=0.0.0.0 steep/steep:6.2.0

After a few seconds, you can access Steep’s web interface on http://localhost:8080/.

We will now submit a simple workflow to test if Steep is running correctly. The workflow consists of a single execute action that sleeps for 10 seconds and then quits. Execute the following command:

curl -X POST http://localhost:8080/workflows -d 'api: 4.5.0
actions:
  - type: execute
    service: sleep
    inputs:
      - id: seconds
        value: 10'

The command will return the ID of the submitted workflow. You can monitor the execution in the web interface or by issuing the following command:

curl http://localhost:8080/workflows/<workflow-id>

Replace <workflow-id> with the returned ID.

Congratulations! You successfully installed Steep and ran your first workflow.

Documentation

In this section, we describe the individual features of Steep. The documentation always applies to the latest software version.

How does Steep work?
Example workflows
Data models
Full-text search
HTTP endpoints
Web-based user interface
Configuration
Extending Steep through plugins

1 How does Steep work?

In order to answer this question, we will first describe how Steep transforms scientific workflow graphs into executable units. After that, we will have a look at Steep’s software architecture and what kind of processing services it can execute.

(This section is based on the following publication: Krämer, M. (2020). Capability-Based Scheduling of Scientific Workflows in the Cloud. Proceedings of the 9th International Conference on Data Science, Technology, and Applications DATA, 43–54. https://doi.org/10.5220/0009805400430054)

1.1 Workflow scheduling

Steep is a scientific workflow management system that can be used to control the processing of very large data sets in a distributed environment.

A scientific workflow is typically represented by a directed acyclic graph that describes how an input data set is processed by certain tasks in a given order to produce a desired outcome. Such workflows can become very large with hundreds up to several thousands of tasks processing data volumes ranging from gigabytes to terabytes. The following figure shows a simple example of such a workflow in an extended Petri Net notation proposed by van der Aalst and van Hee (2004).

In this example, an input file is first processed by a task A. This task produces two results. The first one is processed by task B whose result is in turn sent to C. The second result of A is processed by D. The outcomes of C and D are finally processed by task E.

In order to be able to schedule such a workflow in a distributed environment, the graph has to be transformed to individual executable units. Steep follows a hybrid scheduling approach that applies heuristics on the level of the workflow graph and later on the level of individual executable units. We assume that tasks that access the same data should be executed on the same machine to reduce the communication overhead and to improve file reuse. We therefore group tasks into so-called process chains, which are linear sequential lists (without branches and loops).

Steep transforms workflows to process chains in an iterative manner. In each iteration, it finds the longest linear sequences of tasks and groups them to process chains. The following animation shows how this works for our example workflow:

Task A will be put into a process chain in iteration 1. Steep then schedules the execution of this process chain. After the execution has finished, Steep uses the results to produce a process chain containing B and C and another one containing D. These process chains are then scheduled to be executed in parallel. The results are finally used to generate the fourth process chain containing task E, which is also scheduled for execution.

1.2 Software architecture

The following figure shows the main components of Steep: the HTTP server, the controller, the scheduler, the agent, and the cloud manager.

Together, these components form an instance of Steep. In practice, a single instance typically runs on a separate virtual machine, but multiple instances can also be started on the same machine. Each component can be enabled or disabled in a given instance (see the configuration options for more information). That means, in a cluster, there can be instances that have all five components enabled, and others that have only an agent, for example.

All components of all instances communicate with each other through messages sent over an event bus. Further, the HTTP server, the controller, and the scheduler are able to connect to a shared database.

The HTTP server provides information about scheduled, running, and finished workflows to clients. Clients can also upload a new workflow. In this case, the HTTP server puts the workflow into the database and sends a message to one of the instances of the controller.

The controller receives this message, loads the workflow from the database, and starts transforming it iteratively to process chains as described above. Whenever it has generated new process chains, it puts them into the database and sends a message to all instances of the scheduler.

The schedulers then select agents to execute the process chains. They load the process chains from the database, send them via the event bus to the selected agents for execution, and finally write the results into the database. The schedulers also send a message back to the controller so it can continue with the next iteration and generate more process chains until the workflow has been completely transformed.

In case a scheduler does not find an agent suitable for the execution of a process chain, it sends a message to the cloud manager (a component that interacts with the API of the Cloud infrastructure) and asks it to create a new agent.

1.3 Processing services

Steep is very flexible and allows a wide range of processing services (or microservices) to be integrated. A typical processing service is a program that reads one or more input files and writes one or more output files. The program may also accept generic parameters. The service can be implemented in any programming language (as long as the binary or script is executable on the machine the Steep agent is running) or can be wrapped in a Docker container.

For a seamless integration, a processing service should adhere to the following guidelines:

Every processing service should be a microservice. It should run in its own process and serve one specific purpose.
As Steep needs to call the service in a distributed environment, it should not have a graphical user interface or require any human interaction during the runtime. Suitable services are command-line applications that accept arguments to specify input files, output files, and parameters.
The service should read from input files, process the data, write results to output files, and then exit. It should not run continuously like a web service. If you need to integrate a web service in your workflow, we recommend using the curl command or something similar.
Steep does not require the processing services to implement a specific interface. Instead, the service’s input and output parameters should be described in a special data model called service metadata.
According to common conventions for exit codes, a processing service should return 0 (zero) upon successful execution and any number but zero in case an error has occurred (e.g. 1, 2, 128, 255, etc.).
In order to ensure deterministic workflow executions, services should be stateless and idempotent. This means that every execution of a service with the same input data and the same set of parameters should produce the same result.

2 Example workflows

In this section, we describe example workflows covering patterns we regularly see in real-world use cases. For each workflow, we also provide the required service metadata. For more information about the workflow model and service metadata, please read the section on data models.

2.1 Running two services in parallel

This example workflow consists of two execute actions that each copy a file. Since both actions do not depend on each other (i.e. they do not share any variable), Steep converts them to two independent process chains and executes them in parallel (as long as there are at least two agents available).

The two execute actions refer to the copy service. The service metadata of copy defines that this processing service has an input parameter input_file and an output parameter output_file, both of which must be specified exactly one time (cardinality equals 1..1).

The input parameters are given (example1.txt and example2.txt). The output parameters refer to the variables outputFile1 and outputFile2 and have no value. Steep will create unique values (output file names) for them during the workflow execution.

Workflow:

YAML
JSON
api: 4.5.0
actions:
  - type: execute
    service: copy
    inputs:
      - id: input_file
        value: example1.txt
    outputs:
      - id: output_file
        var: outputFile1
  - type: execute
    service: copy
    inputs:
      - id: input_file
        value: example2.txt
    outputs:
      - id: output_file
        var: outputFile2
{
  "api": "4.5.0",
  "actions": [{
    "type": "execute",
    "service": "copy",
    "inputs": [{
      "id": "input_file",
      "value": "example1.txt"
    }],
    "outputs": [{
      "id": "output_file",
      "var": "outputFile1"
    }]
  }, {
    "type": "execute",
    "service": "copy",
    "inputs": [{
      "id": "input_file",
      "value": "example2.txt"
    }],
    "outputs": [{
      "id": "output_file",
      "var": "outputFile2"
    }]
  }]
}

Service metadata:

YAML
JSON
- id: copy
  name: Copy
  description: Copy files
  path: cp
  runtime: other
  parameters:
    - id: input_file
      name: Input file name
      description: Input file name
      type: input
      cardinality: 1..1
      dataType: file
    - id: output_file
      name: Output file name
      description: Output file name
      type: output
      cardinality: 1..1
      dataType: file
[{
  "id": "copy",
  "name": "Copy",
  "description": "Copy files",
  "path": "cp",
  "runtime": "other",
  "parameters": [{
    "id": "input_file",
    "name": "Input file name",
    "description": "Input file name",
    "type": "input",
    "cardinality": "1..1",
    "dataType": "file"
  }, {
    "id": "output_file",
    "name": "Output file name",
    "description": "Output file name",
    "type": "output",
    "cardinality": "1..1",
    "dataType": "file"
  }]
}]

2.2 Chaining two services

The following example workflow makes a copy of a file and then a copy of the copy (i.e. the file is copied and the result is copied again). The workflow contains two actions that share the same variable: outputFile1 is used as the output of the first action and as the input of the second action. Steep executes them in sequence.

The service metadata for this workflow is the same as for the previous one.

Workflow:

YAML
JSON
api: 4.5.0
actions:
  - type: execute
    service: copy
    inputs:
      - id: input_file
        value: example.txt
    outputs:
      - id: output_file
        var: outputFile1
  - type: execute
    service: copy
    inputs:
      - id: input_file
        var: outputFile1
    outputs:
      - id: output_file
        var: outputFile2
{
  "api": "4.5.0",
  "actions": [{
    "type": "execute",
    "service": "copy",
    "inputs": [{
      "id": "input_file",
      "value": "example.txt"
    }],
    "outputs": [{
      "id": "output_file",
      "var": "outputFile1"
    }]
  }, {
    "type": "execute",
    "service": "copy",
    "inputs": [{
      "id": "input_file",
      "var": "outputFile1"
    }],
    "outputs": [{
      "id": "output_file",
      "var": "outputFile2"
    }]
  }]
}

2.3 Splitting and joining results

This example starts with an action that copies a file. Two other actions then run in parallel and make copies of the result of the first action. A final action then joins these copies to a single file. The workflow has a split-and-join pattern because the graph is split into two branches after the first action. These branches are then joined into a single one with the final action.

Workflow:

YAML
JSON
api: 4.5.0
actions:
  - type: execute
    service: copy
    inputs:
      - id: input_file
        value: example.txt
    outputs:
      - id: output_file
        var: outputFile1
  - type: execute
    service: copy
    inputs:
      - id: input_file
        var: outputFile1
    outputs:
      - id: output_file
        var: outputFile2
  - type: execute
    service: copy
    inputs:
      - id: input_file
        var: outputFile1
    outputs:
      - id: output_file
        var: outputFile3
  - type: execute
    service: join
    inputs:
      - id: i
        var: outputFile2
      - id: i
        var: outputFile3
    outputs:
      - id: o
        var: outputFile4
{
  "api": "4.5.0",
  "actions": [{
    "type": "execute",
    "service": "copy",
    "inputs": [{
      "id": "input_file",
      "value": "example.txt"
    }],
    "outputs": [{
      "id": "output_file",
      "var": "outputFile1"
    }]
  }, {
    "type": "execute",
    "service": "copy",
    "inputs": [{
      "id": "input_file",
      "var": "outputFile1"
    }],
    "outputs": [{
      "id": "output_file",
      "var": "outputFile2"
    }]
  }, {
    "type": "execute",
    "service": "copy",
    "inputs": [{
      "id": "input_file",
      "var": "outputFile1"
    }],
    "outputs": [{
      "id": "output_file",
      "var": "outputFile3"
    }]
  }, {
    "type": "execute",
    "service": "join",
    "inputs": [{
      "id": "i",
      "var": "outputFile2"
    }, {
      "id": "i",
      "var": "outputFile3"
    }],
    "outputs": [{
      "id": "o",
      "var": "outputFile4"
    }]
  }]
}

Service metadata:

YAML
JSON
- id: copy
  name: Copy
  description: Copy files
  path: cp
  runtime: other
  parameters:
    - id: input_file
      name: Input file name
      description: Input file name
      type: input
      cardinality: 1..1
      dataType: file
    - id: output_file
      name: Output file name
      description: Output file name
      type: output
      cardinality: 1..1
      dataType: file
- id: join
  name: Join
  description: Merge one or more files into one
  path: join.sh
  runtime: other
  parameters:
    - id: i
      name: Input files
      description: One or more input files to merge
      type: input
      cardinality: 1..n
      dataType: file
    - id: o
      name: Output file
      description: The output file
      type: output
      cardinality: 1..1
      dataType: file
[{
  "id": "copy",
  "name": "Copy",
  "description": "Copy files",
  "path": "cp",
  "runtime": "other",
  "parameters": [{
    "id": "input_file",
    "name": "Input file name",
    "description": "Input file name",
    "type": "input",
    "cardinality": "1..1",
    "dataType": "file"
  }, {
    "id": "output_file",
    "name": "Output file name",
    "description": "Output file name",
    "type": "output",
    "cardinality": "1..1",
    "dataType": "file"
  }]
}, {
  "id": "join",
  "name": "Join",
  "description": "Merge one or more files into one",
  "path": "join.sh",
  "runtime": "other",
  "parameters": [{
    "id": "i",
    "name": "Input files",
    "description": "One or more input files to merge",
    "type": "input",
    "cardinality": "1..n",
    "dataType": "file"
  }, {
    "id": "o",
    "name": "Output file",
    "description": "The output file",
    "type": "output",
    "cardinality": "1..1",
    "dataType": "file"
  }]
}]

2.4 Processing a dynamic number of results in parallel

This example demonstrates how to process the results of an action in parallel even if the number of result files is unknown during the design of the workflow. The workflow starts with an action that splits an input file example.txt into multiple files (e.g. one file per line) stored in a directory outputDirectory. A for-each action then iterates over these files and creates copies. The for-each action has an iterator i that serves as the input for the individual instances of the copy service. The output files (outputFile1) of this service are collected via the yieldToOutput property in a variable called copies. The final join service merges these copies into a single file outputFile2.

Workflow:

YAML
JSON
api: 4.5.0
actions:
  - type: execute
    service: split
    inputs:
      - id: file
        value: example.txt
      - id: lines
        value: 1
    outputs:
      - id: output_directory
        var: outputDirectory
  - type: for
    input: outputDirectory
    enumerator: i
    output: copies
    actions:
      - type: execute
        service: copy
        inputs:
          - id: input_file
            var: i
        outputs:
          - id: output_file
            var: outputFile1
    yieldToOutput: outputFile1
  - type: execute
    service: join
    inputs:
      - id: i
        var: copies
    outputs:
      - id: o
        var: outputFile2
{
  "api": "4.5.0",
  "actions": [{
    "type": "execute",
    "service": "split",
    "inputs": [{
      "id": "file",
      "value": "example.txt"
    }, {
      "id": "lines",
      "value": 1
    }],
    "outputs": [{
      "id": "output_directory",
      "var": "outputDirectory"
    }]
  }, {
    "type": "for",
    "input": "outputDirectory",
    "enumerator": "i",
    "output": "copies",
    "actions": [{
      "type": "execute",
      "service": "copy",
      "inputs": [{
        "id": "input_file",
        "var": "i"
      }],
      "outputs": [{
        "id": "output_file",
        "var": "outputFile1"
      }]
    }],
    "yieldToOutput": "outputFile1"
  }, {
    "type": "execute",
    "service": "join",
    "inputs": [{
      "id": "i",
      "var": "copies"
    }],
    "outputs": [{
      "id": "o",
      "var": "outputFile2"
    }]
  }]
}

Service metadata:

YAML
JSON
- id: split
  name: Split
  description: Split a file into pieces
  path: split
  runtime: other
  parameters:
    - id: lines
      name: Number of lines per file
      description: Create smaller files n lines in length
      type: input
      cardinality: 0..1
      dataType: integer
      label: '-l'
    - id: file
      name: Input file
      description: The input file to split
      type: input
      cardinality: 1..1
      dataType: file
    - id: output_directory
      name: Output directory
      description: The output directory
      type: output
      cardinality: 1..1
      dataType: directory
      fileSuffix: /
- id: copy
  name: Copy
  description: Copy files
  path: cp
  runtime: other
  parameters:
    - id: input_file
      name: Input file name
      description: Input file name
      type: input
      cardinality: 1..1
      dataType: file
    - id: output_file
      name: Output file name
      description: Output file name
      type: output
      cardinality: 1..1
      dataType: file
- id: join
  name: Join
  description: Merge one or more files into one
  path: join.sh
  runtime: other
  parameters:
    - id: i
      name: Input files
      description: One or more input files to merge
      type: input
      cardinality: 1..n
      dataType: file
    - id: o
      name: Output file
      description: The output file
      type: output
      cardinality: 1..1
      dataType: file
[{
  "id": "split",
  "name": "Split",
  "description": "Split a file into pieces",
  "path": "split",
  "runtime": "other",
  "parameters": [{
    "id": "lines",
    "name": "Number of lines per file",
    "description": "Create smaller files n lines in length",
    "type": "input",
    "cardinality": "0..1",
    "dataType": "integer",
    "label": "-l"
  }, {
    "id": "file",
    "name": "Input file",
    "description": "The input file to split",
    "type": "input",
    "cardinality": "1..1",
    "dataType": "file"
  }, {
    "id": "output_directory",
    "name": "Output directory",
    "description": "The output directory",
    "type": "output",
    "cardinality": "1..1",
    "dataType": "directory",
    "fileSuffix": "/"
  }]
}, {
  "id": "copy",
  "name": "Copy",
  "description": "Copy files",
  "path": "cp",
  "runtime": "other",
  "parameters": [{
    "id": "input_file",
    "name": "Input file name",
    "description": "Input file name",
    "type": "input",
    "cardinality": "1..1",
    "dataType": "file"
  }, {
    "id": "output_file",
    "name": "Output file name",
    "description": "Output file name",
    "type": "output",
    "cardinality": "1..1",
    "dataType": "file"
  }]
}, {
  "id": "join",
  "name": "Join",
  "description": "Merge one or more files into one",
  "path": "join.sh",
  "runtime": "other",
  "parameters": [{
    "id": "i",
    "name": "Input files",
    "description": "One or more input files to merge",
    "type": "input",
    "cardinality": "1..n",
    "dataType": "file"
  }, {
    "id": "o",
    "name": "Output file",
    "description": "The output file",
    "type": "output",
    "cardinality": "1..1",
    "dataType": "file"
  }]
}]

2.5 Feeding results back into the workflow (cycles/loops)

The following example shows how to create loops with a dynamic number of iterations. Suppose there is a processing service called countdown.js that reads a number from an input file, decreases this number by 1, and then writes the result to an output file. The service could be implemented in Node.js as follows:

#!/usr/bin/env node

const fs = require("fs").promises

async function countDown(input, output) {
  let value = parseInt(await fs.readFile(input, "utf-8"))
  console.log(`Old value: ${value}`)

  value--
  if (value > 0) {
    console.log(`New value: ${value}`)
    await fs.writeFile(output, "" + value, "utf-8")
  } else {
    console.log("No new value")
  }
}

countDown(process.argv[2], process.argv[3])

The following workflow uses this service in a for-each action to continuously reprocess a file and decrease the number in it until it reaches 0.

In the first iteration of the for-each action, the service reads from a file called input.txt and writes to an output file with a name generated during runtime. The path of this output file is routed back into the for-each action via yieldToInput. In the second iteration, the service reads from the output file and produces another one. This process continues until the number equals 0. In this case, the service does not write an output file anymore and the workflow finishes.

Note that we use the data type fileOrEmptyList in the service metadata for the output parameter of the countdown service. This is a special data type that either returns the generated file or an empty list if the file does not exist. In the latter case, the for-each action does not have any more input values to process. Think of the input of a for-each action as a queue. If nothing is pushed into the queue and all elements have already been processed, the for-each action can finish.

Workflow:

YAML
JSON
api: 4.5.0
vars:
  - id: input_file
    value: input.txt
actions:
  - type: for
    input: input_file
    enumerator: i
    yieldToInput: output_file
    actions:
      - type: execute
        service: countdown
        inputs:
          - id: input
            var: i
        outputs:
          - id: output
            var: output_file
{
  "api": "4.5.0",
  "vars": [{
    "id": "input_file",
    "value": "input.txt"
  }],
  "actions": [{
    "type": "for",
    "input": "input_file",
    "enumerator": "i",
    "yieldToInput": "output_file",
    "actions": [{
      "type": "execute",
      "service": "countdown",
      "inputs": [{
        "id": "input",
        "var": "i"
      }],
      "outputs": [{
        "id": "output",
        "var": "output_file"
      }]
    }]
  }]
}

Service metadata:

YAML
JSON
- id: countdown
  name: Count Down
  description: Read a number, subtract 1, and write the result
  path: ./countdown.js
  runtime: other
  parameters:
    - id: input
      name: Input file
      description: The input file containing the number to decrease
      type: input
      cardinality: 1..1
      dataType: file
    - id: output
      name: Output file
      description: The path to the output file
      type: output
      cardinality: 1..1
      dataType: fileOrEmptyList
[{
  "id": "countdown",
  "name": "Count Down",
  "description": "Read a number, subtract 1, and write the result",
  "path": "./countdown.js",
  "runtime": "other",
  "parameters": [{
    "id": "input",
    "name": "Input file",
    "description": "The input file containing the number to decrease",
    "type": "input",
    "cardinality": "1..1",
    "dataType": "file"
  }, {
    "id": "output",
    "name": "Output file",
    "description": "The path to the output file",
    "type": "output",
    "cardinality": "1..1",
    "dataType": "fileOrEmptyList"
  }]
}]

3 Data models

This section contains a description of all data models used by Steep.

3.1 Workflows

The main components of the workflow model are variables and actions. Use variables to specify input files and parameters for your processing services. Variables for output files must also be declared but must not have a value. The names of output files will be generated by Steep during the runtime of the workflow.

Property	Type	Description
api (required)	string	The API (or data model) version. Should be `4.5.0`.
name (optional)	string	An optional human-readable workflow name
priority (optional)	number	A priority used during scheduling. Process chains generated from workflows with higher priorities will be scheduled before those with lower priorities. Negative values are allowed. The default value is `0`.
vars (optional)	array	An array of variables
actions (required)	array	An array of actions that make up the workflow

Example:

See the section on example workflows.

3.2 Variables

A variable holds a value for inputs and outputs of processing services. It can be defined (inputs) or undefined (outputs). Defined values are immutable. Undefined variables will be assigned a value by Steep during the runtime of a workflow.

Variables are also used to link two services together and to define the data flow in the workflow graph. For example, if the output parameter of a service A refers to a variable V, and the input parameter of service B refers to the same variable, Steep will first execute A to determine the value of V and then execute B.

Property	Type	Description
id (required)	string	A unique variable identifier
value (optional)	any	The variable’s value or `null` if the variable is undefined

Example:

YAML
JSON
id: input_file
value: /data/input.txt
{
  "id": "input_file",
  "value": "/data/input.txt"
}

3.3 Actions

There are two types of actions in a workflow: execute actions and for-each actions. They are differentiated by their type attribute.

3.3.1 Execute actions

An execute action instructs Steep to execute a certain service with given inputs and outputs.

Property	Type	Description
id (optional)	string	An optional string uniquely identifying the action within the workflow. If not given, a random identifier will be generated.
type (required)	string	The type of the action. Must be `"execute"`.
service (required)	string	The ID of the service to execute
inputs (optional)	array	An array of input parameters
outputs (optional)	array	An array of output parameters
dependsOn (optional)	array	A list of identifiers of actions this action needs to finish first before it is ready to be executed. Note that Steep is able to identify dependencies between actions itself based on `outputs` and `inputs`, so this attribute is normally not needed. However, it may be useful if a preceding action does not have an output parameter or if the depending action does not have an input parameter. Execute actions may depend on other execute actions but also on for-each actions and vice versa.
retries (optional)	object	An optional retry policy specifying how often this action should be retried in case of an error. Overrides any default retry policy defined in the service metadata.
maxInactivity (optional)	duration or object	An optional duration or timeout policy that defines how long the execution of the service can take without producing any output (i.e. without writing anything to the standard output and error streams) before it is automatically cancelled or aborted. Can be combined with `maxRuntime` and `deadline` (see below). Overrides any default inactivity timeout defined in the service metadata. Note that a service cancelled due to inactivity is still subject to any configured retry policy, which means its execution may be retried even if one attempt timed out. If you want to cancel a long-running service immediately even if there is a retry policy configured, use a `deadline`.
maxRuntime (optional)	duration or object	An optional duration or timeout policy that defines how long the execution of the service can take before it is automatically cancelled or aborted, even if the service regularly writes to the standard output and error streams. Can be combined with `maxInactivity` (see above) and `deadline` (see below). Overrides any default maximum runtime defined in the service metadata. Note that a service cancelled due to a too long runtime is still subject to any configured retry policy, which means its execution may be retried even if one attempt timed out. If you want to cancel a long-running service immediately even if there is a retry policy configured, use a `deadline`.
deadline (optional)	duration or object	An optional duration or timeout policy that defines how long the execution of the service can take at all (including all retries and their associated delays) until it is cancelled or aborted. Can be combined with `maxInactivity` and `maxRuntime` (see above). Overrides any default deadline defined in the service metadata.

Example:

YAML
JSON
type: execute
service: my_service
inputs:
  - id: verbose
    var: is_verbose
  - id: resolution
    value: 10
  - id: input_file
    var: my_input_file
outputs:
  - id: output_file
    var: my_output_file
    store: true
{
  "type": "execute",
  "service": "my_service",
  "inputs": [{
    "id": "verbose",
    "var": "is_verbose"
  }, {
    "id": "resolution",
    "value": 10
  }, {
    "id": "input_file",
    "var": "my_input_file"
  }],
  "outputs": [{
    "id": "output_file",
    "var": "my_output_file",
    "store": true
  }]
}

3.3.2 For-each actions

A for-each action has an input, a list of sub-actions, and an output. It clones the sub-actions as many times as there are items in its input, executes the actions, and then collects the results in the output.

Although the action is called ‘for-each’, the execution order of the sub-actions is undefined (i.e. the execution is non-sequential and non-deterministic). Instead, Steep always tries to execute as many sub-actions as possible in parallel.

For-each actions may contain execute actions but also nested for-each actions.

Property	Type	Description
id (optional)	string	An optional string uniquely identifying the action within the workflow. If not given, a random identifier will be generated.
type (required)	string	The type of the action. Must be `"for"`.
input (required)	string	The ID of a variable containing the items to which to apply the sub-actions
enumerator (required)	string	The ID of a variable that holds the current value from `input` for each iteration
output (optional)	string	The ID of a variable that will collect output values from all iterations (see `yieldToOutput`)
dependsOn (optional)	array	A list of identifiers of actions this action needs to finish first before it is ready to be executed. Note that Steep is able to identify dependencies between actions itself based on `outputs` and `inputs`, so this attribute is normally not needed. However, it may be useful if a preceding action does not have an output parameter or if the depending action does not have an input parameter. For-each actions may depend on execute actions but also on other for-each actions and vice versa.
actions (optional)	array	An array of sub-actions to execute in each iteration
yieldToOutput (optional)	string	The ID of a sub-action’s output variable whose value should be appended to the for-each action’s `output`
yieldToInput (optional)	string	The ID of a sub-action’s output variable whose value should be appended to the for-each action’s `input` to generate further iterations

Example:

YAML
JSON
type: for
input: all_input_files
output: all_output_files
enumerator: i
yieldToOutput: output_file
actions:
  - type: execute
    service: copy
    inputs:
      - id: input
        var: i
    outputs:
      - id: output
        var: output_file
{
  "type": "for",
  "input": "all_input_files",
  "output": "all_output_files",
  "enumerator": "i",
  "yieldToOutput": "output_file",
  "actions": [{
    "type": "execute",
    "service": "copy",
    "inputs": [{
      "id": "input",
      "var": "i"
    }],
    "outputs": [{
      "id": "output",
      "var": "output_file"
    }]
  }]
}

3.3.3 Parameters

This data model represents inputs and generic parameters of execute actions.

Property	Type	Description
id (required)	string	The ID of the parameter as defined in the service metadata
var (optional)	string	The ID of a variable that holds the value for this parameter (required if `value` is not given)
value (optional)	any	The parameter value (required if `var` is not given)

Note: Either var or value must be given but not both!

Example:

YAML
JSON
id: input
var: i
{
  "id": "input",
  "var": "i"
}

3.3.4 Output parameters

Output parameters of execute actions have additional properties compared to inputs.

Property	Type	Description
id (required)	string	The ID of the parameter as defined in the service metadata
var (required)	string	The ID of a variable to which Steep will assign the generated name of the output file. This variable can then be used, for example, as an input parameter of a subsequent action.
prefix (optional)	string	An optional string to prepend to the generated name of the output file. For example, if Steep generates the name `"name123abc"` and the prefix is `"my/dir/"`, the output filename will be `"my/dir/name123abc"`. Note that the prefix must end with a slash if you want to create a directory. The output filename will be relative to the configured temporary directory or output directory (depending on the `store` property). You may even specify an absolute path: if the generated name is `"name456fgh"` and the prefix is `"/absolute/dir/"`, the output filename will be `"/absolute/dir/name456fgh"`.
store (optional)	boolean	If this property is `true`, Steep will generate an output filename that is relative to the configured output directory instead of the temporary directory. The default value is `false`.

Example:

YAML
JSON
id: output
var: o
prefix: some_directory/
store: false
{
  "id": "output",
  "var": "o",
  "prefix": "some_directory/",
  "store": false
}

3.4 Process chains

As described above, Steep transforms a workflow to one or more process chains. A process chain is a sequential list of instructions that will be sent to Steep’s remote agents to execute processing services in a distributed environment.

Property	Type	Description
id (required)	string	Unique process chain identifier
executables (required)	array	A list of executable objects that describe what processing services should be called and with which arguments
submissionId (required)	string	The ID of the submission to which this process chain belongs
startTime (optional)	string	An ISO 8601 timestamp denoting the date and time when the process chain execution was started. May be `null` if the execution has not started yet.
endTime (optional)	string	An ISO 8601 timestamp denoting the date and time when the process chain execution finished. May be `null` if the execution has not finished yet.
status (required)	string	The current status of the process chain
requiredCapabilities (optional)	array	A set of strings specifying capabilities a host system must provide to be able to execute this process chain. See also setups.
priority (optional)	number	A priority used during scheduling. Process chains with higher priorities will be scheduled before those with lower priorities. Negative values are allowed. The default value is `0`.
results (optional)	object	If `status` is `SUCCESS`, this property contains the list of process chain result files grouped by their output variable ID. Otherwise, it is `null`.
estimatedProgress (optional)	number	A floating point number between `0.0` (0%) and `1.0` (100%) indicating the current execution progress of this process chain. This property will only be provided if the process chain is currently being executed (i.e. if its `status` equals `RUNNING`) and if a progress could actually be estimated. Note that the value is an estimation based on various factors and does not have to represent the real progress. More precise values can be calculated with a progress estimator plugin. Sometimes, progress cannot be estimated at all. In this case, the value will be `null`.
errorMessage (optional)	string	If `status` is `ERROR`, this property contains a human-readable error message. Otherwise, it is `null`.

Example:

YAML
JSON
id: akpm646jjigral4cdyyq
submissionId: akpm6yojjigral4cdxgq
startTime: '2020-05-18T08:44:19.221456Z'
endTime: '2020-05-18T08:44:19.446437Z'
status: SUCCESS
requiredCapabilities:
  - nodejs
executables:
  - id: ayj5kegaxngbglzlxibq
    path: ./countdown.js
    serviceId: countdown
    runtime: other
    arguments:
      - id: input
        type: input
        dataType: file
        variable:
          id: input_file
          value: input.txt
      - id: output
        type: output
        dataType: fileOrEmptyList
        variable:
          id: output_file
          value: output.txt
    runtimeArgs: []
results:
  output_file:
    - output.txt
{
  "id": "akpm646jjigral4cdyyq",
  "submissionId": "akpm6yojjigral4cdxgq",
  "startTime": "2020-05-18T08:44:19.221456Z",
  "endTime": "2020-05-18T08:44:19.446437Z",
  "status": "SUCCESS",
  "requiredCapabilities": ["nodejs"],
  "executables": [{
    "id": "ayj5kegaxngbglzlxibq",
    "path": "./countdown.js",
    "serviceId": "countdown",
    "runtime": "other",
    "arguments": [{
      "id": "input",
      "type": "input",
      "dataType": "file",
      "variable": {
        "id": "input_file",
        "value": "input.txt"
      }
    }, {
      "id": "output",
      "type": "output",
      "dataType": "fileOrEmptyList",
      "variable": {
        "id": "output_file",
        "value": "output.txt"
      }
    }],
    "runtimeArgs": []
  }],
  "results": {
    "output_file": ["output.txt"]
  }
}

3.4.1 Process chain status

The following table shows the statuses a process chain can have:

Status	Description
REGISTERED	The process chain has been created but execution has not started yet
RUNNING	The process chain is currently being executed
CANCELLED	The execution of the process chain was cancelled
SUCCESS	The process chain was executed successfully
ERROR	The execution of the process chain failed

3.5 Executables

An executable is part of a process chain. It describes how a processing service should be executed and with which parameters.

Property	Type	Description
id (required)	string	An identifier (does not have to be unique). Typically refers to the `id` of the execute action, from which the executable was derived. Possibly suffixed with a dollar sign `$` and a number denoting the iteration of an enclosing for-each action (e.g. `myaction$1`) or nested for-each actions (e.g. `myaction$2$1`).
path (required)	string	The path to the binary of the service to be executed. This property is specific to the `runtime`. For example, for the `docker` runtime, this property refers to the Docker image.
serviceId (required)	string	The ID of the processing service to be executed.
arguments (required)	array	A list of arguments to pass to the service. May be empty.
runtime (required)	string	The name of the runtime that will execute the service. Built-in runtimes are currently `other` (for any service that is executable on the target system) and `docker` for Docker containers. More runtimes can be added through plugins
runtimeArgs (optional)	array	A list of arguments to pass to the runtime. May be empty.
retries (optional)	object	An optional retry policy specifying how often this executable should be restarted in case of an error.
maxInactivity (optional)	object	An optional timeout policy that defines how long the executable can run without producing any output (i.e. without writing anything to the standard output and error streams) before it is automatically cancelled or aborted.
maxRuntime (optional)	object	An optional timeout policy that defines how long the executable can run before it is automatically cancelled or aborted, even if the service regularly writes to the standard output and error streams.
deadline (optional)	object	An optional timeout policy that defines how long the executable can run at all (including all retries and their associated delays) until it is cancelled or aborted.

Example:

YAML
JSON
id: ayj5kiwaxngbglzlxica
path: my_docker_image:latest
serviceId: countdown
runtime: docker
arguments:
  - id: input
    type: input
    dataType: file
    variable:
      id: input_file
      value: /data/input.txt
  - id: output
    type: output
    dataType: directory
    variable:
      id: output_file
      value: /data/output
  - id: arg1
    type: input
    dataType: boolean
    label: '--foobar'
    variable:
      id: akqcqqoedcsaoescyhga
      value: 'true'
runtimeArgs:
  - id: akqcqqoedcsaoescyhgq
    type: input
    dataType: string
    label: '-v'
    variable:
      id: data_mount
      value: /data:/data
{
  "id": "ayj5kiwaxngbglzlxica",
  "path": "my_docker_image:latest",
  "serviceId": "countdown",
  "runtime": "docker",
  "arguments": [{
    "id": "input",
    "type": "input",
    "dataType": "file",
    "variable": {
      "id": "input_file",
      "value": "/data/input.txt"
    }
  }, {
    "id": "output",
    "type": "output",
    "dataType": "directory",
    "variable": {
      "id": "output_file",
      "value": "/data/output"
    }
  }, {
    "id": "arg1",
    "type": "input",
    "dataType": "boolean",
    "label": "--foobar",
    "variable": {
      "id": "akqcqqoedcsaoescyhga",
      "value": "true"
    }
  }],
  "runtimeArgs": [{
    "id": "akqcqqoedcsaoescyhgq",
    "type": "input",
    "dataType": "string",
    "label": "-v",
    "variable": {
      "id": "data_mount",
      "value": "/data:/data"
    }
  }]
}

3.5.1 Arguments

An argument is part of an executable.

Property	Type	Description
id (required)	string	An argument identifier
label (optional)	string	An optional label to use when the argument is passed to the service (e.g. `--input`).
variable (required)	object	A variable that holds the value of this argument.
type (required)	string	The type of this argument. Valid values: `input`, `output`
dataType (required)	string	The type of the argument value. If this property is `directory`, Steep will create a new directory for the service’s output and recursively search it for result files after the service has been executed. Otherwise, this property can be an arbitrary string. New data types with special handling can be added through output adapter plugins.

Example:

YAML
JSON
id: akqcqqoedcsaoescyhgq
type: input
dataType: string
label: '-v'
variable:
  id: data_mount
  value: /data:/data
{
  "id": "akqcqqoedcsaoescyhgq",
  "type": "input",
  "dataType": "string",
  "label": "-v",
  "variable": {
    "id": "data_mount",
    "value": "/data:/data"
  }
}

3.5.2 Argument variables

An argument variable holds the value of an argument.

Property	Type	Description
id (required)	string	The variable’s unique identifier
value (required)	string	The variable’s value

Example:

YAML
JSON
id: data_mount
value: /data:/data
{
  "id": "data_mount",
  "value": "/data:/data"
}

3.6 Submissions

A submission is created when you submit a workflow through the /workflows endpoint. It contains information about the workflow execution such as the start and end time as well as the current status.

Property	Type	Description
id (required)	string	Unique submission identifier
name (optional)	string	An optional human-readable submission name. The value is derived from the submitted workflow’s name if it has any.
workflow (required)	object	The submitted workflow
priority (optional)	number	A priority used during scheduling. Process chains generated from submissions with higher priorities will be scheduled before those with lower priorities. Negative values are allowed. The value is derived from the submitted workflow but can be overridden. The submission’s priority always takes precedence over the workflow’s priority when generating process chains.
startTime (optional)	string	An ISO 8601 timestamp denoting the date and time when the workflow execution was started. May be `null` if the execution has not started yet.
endTime (optional)	string	An ISO 8601 timestamp denoting the date and time when the workflow execution finished. May be `null` if the execution has not finished yet.
status (required)	string	The current status of the submission
requiredCapabilities (required)	array	A set of strings specifying capabilities a host system must provide to be able to execute this workflow. See also setups.
source (optional)	string	The original, unaltered workflow source as it was submitted through the `/workflows` endpoint. May be `null` if the workflow was not submitted through the endpoint or if the source is unavailable.
runningProcessChains (required)	number	The number of process chains currently being executed
cancelledProcessChains (required)	number	The number of process chains that have been cancelled
succeededProcessChains (required)	number	The number of process chains that have finished successfully
failedProcessChains (required)	number	The number of process chains whose execution has failed
totalProcessChains (required)	number	The current total number of process chains in this submission. May increase during execution when new process chains are generated.
results (optional)	object	If `status` is `SUCCESS` or `PARTIAL_SUCCESS`, this property contains the list of workflow result files grouped by their output variable ID. Otherwise, it is `null`.
errorMessage (optional)	string	If `status` is `ERROR`, this property contains a human-readable error message. Otherwise, it is `null`.

Example:

YAML
JSON
id: aiq7eios7ubxglkcqx5a
workflow:
  api: 4.5.0
  vars:
    - id: myInputFile
      value: /data/input.txt
    - id: myOutputFile
  actions:
    - type: execute
      service: cp
      inputs:
        - id: input_file
          var: myInputFile
      outputs:
        - id: output_file
          var: myOutputFile
          store: true
startTime: '2020-02-13T15:38:58.719382Z'
endTime: '2020-02-13T15:39:00.807715Z'
status: SUCCESS
runningProcessChains: 0
cancelledProcessChains: 0
succeededProcessChains: 1
failedProcessChains: 0
totalProcessChains: 1
results:
  myOutputFile:
    - /data/out/aiq7eios7ubxglkcqx5a/aiq7hygs7ubxglkcrf5a
{
  "id": "aiq7eios7ubxglkcqx5a",
  "workflow": {
    "api": "4.5.0",
    "vars": [{
      "id": "myInputFile",
      "value": "/data/input.txt"
    }, {
      "id": "myOutputFile"
    }],
    "actions": [{
      "type": "execute",
      "service": "cp",
      "inputs": [{
        "id": "input_file",
        "var": "myInputFile"
      }],
      "outputs": [{
        "id": "output_file",
        "var": "myOutputFile",
        "store": true
      }]
    }]
  },
  "startTime": "2020-02-13T15:38:58.719382Z",
  "endTime": "2020-02-13T15:39:00.807715Z",
  "status": "SUCCESS",
  "runningProcessChains": 0,
  "cancelledProcessChains": 0,
  "succeededProcessChains": 1,
  "failedProcessChains": 0,
  "totalProcessChains": 1,
  "results": {
    "myOutputFile": [
      "/data/out/aiq7eios7ubxglkcqx5a/aiq7hygs7ubxglkcrf5a"
    ]
  }
}

3.6.1 Submission status

The following table shows the statuses a submission can have:

Status	Description
ACCEPTED	The submission has been accepted by Steep but execution has not started yet
RUNNING	The submission is currently being executed
CANCELLED	The submission was cancelled
SUCCESS	The execution of the submission finished successfully
PARTIAL_SUCCESS	The submission was executed completely but one or more process chains failed
ERROR	The execution of the submission failed

3.7 Service metadata

Service metadata is used to describe the interface of a processing service so it can be executed by Steep.

Property	Type	Description
id (required)	string	A unique service identifier
name (required)	string	A human-readable name
description (required)	string	A human-readable description
path (required)	string	Relative path to the service executable in the service artefact (or a Docker image if `runtime` equals `docker`)
runtime (required)	string	The runtime environment
parameters (required)	array	A list of service parameters
runtimeArgs (optional)	array	An optional list of arguments to pass to the runtime
requiredCapabilities (optional)	array	A set of strings specifying capabilities a host system must provide to be able to execute this service. See also setups.
retries (optional)	object	An optional retry policy specifying how often the execution of this service should be retried in case of an error. Can be overridden in an executable action.
maxInactivity (optional)	duration or object	An optional duration or timeout policy that defines how long the execution of this service can take without producing any output (i.e. without writing anything to the standard output and error streams) before it is automatically cancelled or aborted. Can be overridden in an executable action and can be combined with `maxRuntime` and `deadline` (see below). Note that a service cancelled due to inactivity is still subject to any configured retry policy, which means its execution may be retried even if one attempt timed out. If you want to cancel a long-running service immediately even if there is a retry policy configured, use a `deadline`.
maxRuntime (optional)	duration or object	An optional duration or timeout policy that defines how long the execution of this service can take before it is automatically cancelled or aborted, even if the service regularly writes to the standard output and error streams. Can be overridden in an executable action and can be combined with `maxInactivity` (see above) and `deadline` (see below). Note that a service cancelled due to a too long runtime is still subject to any configured retry policy, which means its execution may be retried even if one attempt timed out. If you want to cancel a long-running service immediately even if there is a retry policy configured, use a `deadline`.
deadline (optional)	duration or object	An optional duration or timeout policy that defines how long the execution of this service can take at all (including all retries and their associated delays) until it is cancelled or aborted. Can be overridden in an executable action and can be combined with `maxInactivity` and `maxRuntime` (see above).

Example:

YAML
JSON
id: cp
name: cp
description: Copies files
path: cp
runtime: other
parameters:
  - id: no_overwrite
    name: No overwrite
    description: Do not overwrite existing file
    type: input
    cardinality: 1..1
    label: '-n'
    dataType: boolean
    default: false
  - id: input_file
    name: Input file name
    description: Input file name
    type: input
    cardinality: 1..1
    dataType: file
  - id: output_file
    name: Output file name
    description: Output file name
    type: output
    cardinality: 1..1
    dataType: file
{
  "id": "cp",
  "name": "cp",
  "description": "Copies files",
  "path": "cp",
  "runtime": "other",
  "parameters": [{
    "id": "no_overwrite",
    "name": "No overwrite",
    "description": "Do not overwrite existing file",
    "type": "input",
    "cardinality": "1..1",
    "label": "-n",
    "dataType": "boolean",
    "default": false
  }, {
    "id": "input_file",
    "name": "Input file name",
    "description": "Input file name",
    "type": "input",
    "cardinality": "1..1",
    "dataType": "file"
  }, {
    "id": "output_file",
    "name": "Output file name",
    "description": "Output file name",
    "type": "output",
    "cardinality": "1..1",
    "dataType": "file"
  }]
}

3.7.1 Runtime environments

Steep provides a set of default runtime environments that define how processing services are executed. More environments can be added through runtime environment plugins.

Name	Description
docker	The service will be executed through Docker. The service metadata attribute `path` specifies the Docker image to run. The attribute `runtimeArgs` specifies parameters that should be forwarded to the `docker` `run` command.
other	The service will be executed like a normal executable program (binary or shell script)

3.7.2 Service parameters

This data model describes the parameters that can be passed to a processing service. It is part of the service metadata.

Property	Type	Description
id (required)	string	A unique parameter identifier
name (required)	string	A human-readable name
description (required)	string	A human-readable description
type (required)	string	The type of this parameter. Valid values: `input`, `output`
cardinality (required)	string	A string in the form `lower..upper` specifying how many times the parameter must appear at least (lower limit) and how many times it can appear at most (upper limit). The character `n` can be used for the upper limit to specify an arbitrary number. The lower limit must not be greater that the upper limit. Examples cardinalities are listed below.
dataType (optional)	string	The type of the parameter value. Steep treats parameters differently depending on the data type (see description below).
default (optional)	string	An optional default value for this parameter that will be used if the lower limit of `cardinality` is 1 but no parameter value is given in the workflow.
fileSuffix (optional)	string	An optional suffix that should be appended to the generated filename of an `output` parameter. This property is typically used for file extensions (including the dot), e.g. `".xml"` or `".json"`.
label (optional)	string	An optional string that will be used as a label for the parameter in the service call. Examples are `-i`, `--input`, `--resolution`, etc.

Example cardinalities:

"0..1" means the parameter is optional (it can appear 0 times or 1 time)
"1..1" means the parameter is mandatory (it must appear 1 time)
"1..n" means it must appear at least once or many times (no upper limit)

Data type:

Steep treats parameters differently depending on the type and dataType:

If type is "output" and dataType is "directory", Steep will create a new directory for the service’s output and recursively search it for result files after the service has been executed.
If type is "input" and dataType is "directory", Steep will find the common parent directory of the files from the parameter’s value and pass it to the service. For example, if the parameter’s value is an array with the elements ["/tmp/a.txt", "/tmp/b.txt", "/tmp/subdir/c.txt"], Steep will pass "/tmp/" to the service.
If type is "input", dataType is not "directory", but the parameter’s value is an array, Steep will duplicate the parameter as many times as there are items in the array (given that the cardinality has no upper limit).
If type is "input", dataType is "boolean", and the parameter has a label, Steep will pass the label to the service if the parameter’s value is true and ignore the parameter if the value is false.
Otherwise, this property can be an arbitrary string. New data types with special handling can be added through output adapter plugins.

Example:

YAML
JSON
id: no_overwrite
name: No overwrite
description: Do not overwrite existing file
type: input
cardinality: 1..1
label: '-n'
dataType: boolean
default: false
{
  "id": "no_overwrite",
  "name": "No overwrite",
  "description": "Do not overwrite existing file",
  "type": "input",
  "cardinality": "1..1",
  "label": "-n",
  "dataType": "boolean",
  "default": false
}

3.7.3 Runtime arguments

Runtime arguments are similar to service parameters, except they are passed to the runtime that executes the service (e.g. Docker) instead of the service itself.

Property	Type	Description
id (required)	string	A unique argument identifier
name (required)	string	A human-readable name
description (required)	string	A human-readable description
dataType (optional)	string	The type of the parameter value. Typically `"string"` or `"boolean"`. The same rules apply as for service parameters.
label (optional)	string	An optional string that will be used as a label for the parameter. Examples are `-v`, `--volume`, `--entrypoint`, etc.
value (optional)	string	An optional value for this parameter.

Example:

YAML
JSON
id: volume
name: Volume mount
description: Mount data directory
label: '-v'
value: /data:/data
{
  "id": "volume",
  "name": "Volume mount",
  "description": "Mount data directory",
  "label": "-v",
  "value": "/data:/data"
}

3.8 Retry policies

A retry policy specifies how often the execution of a workflow action should be retried in case of an error. Retry policies can be specified per service in the service metadata or per executable action in the workflow.

Property	Type	Description
maxAttempts (optional)	number	The maximum number of attempts to perform. This includes the initial attempt. For example, a value of `3` means 1 initial attempt and 2 retries. The default value is `1`. A value of `-1` means an unlimited (infinite) number of attempts. `0` means there will be no attempt at all (the service or action will be skipped).
delay (optional)	duration	The amount of time that should pass between two attempts. The default is `0`, which means the operation will be retried immediately.
exponentialBackoff (optional)	number	A factor for an exponential backoff (see description below)
maxDelay (optional)	duration	The maximum amount of time that should pass between two attempts. Only applies if `exponentialBackoff` is larger than `1`. By default, there is no upper limit.

Exponential backoff:

The exponential backoff factor can be used to gradually increase the delay. The actual delay between two attempts will be calculated as follows:

actualDelay = min(delay * pow(exponentialBackoff, nAttempt - 1), maxDelay)

For example, if delay equals 1s, exponentialBackoff equals 2, and maxDelay equals 10s, the following actual delays will apply:

Delay after attempt 1

min(1s * pow(2, 0), 10s) = 1s
Delay after attempt 2:

min(1s * pow(2, 1), 10s) = 2s
Delay after attempt 3:

min(1s * pow(2, 2), 10s) = 4s
Delay after attempt 4:

min(1s * pow(2, 3), 10s) = 8s
Delay after attempt 5:

min(1s * pow(2, 4), 10s) = 10s
Delay after attempt 6:

min(1s * pow(2, 4), 10s) = 10s

The default value is 1, which means there is no backoff and the actual delay always equals the specified one.

Example:

YAML
JSON
maxAttempts: 5
delay: 1s
exponentialBackoff: 2
maxDelay: 10s
{
  "maxAttempts": 5,
  "delay": "1s",
  "exponentialBackoff": 2,
  "maxDelay": "10s"
}

3.9 Timeout policies

A timeout policy defines how long a service or an executable may run before it is automatically cancelled or aborted (with an error). Timeout policies can be specified with the maxInactivity, maxRuntime and deadline attributes, either per service in the service metadata or per executable action in the workflow.

A timeout policy is either a string or an object. If it is a string, it represents a duration specifying a maximum amount of time until the execution is cancelled.

If specified as an object, the timeout policy has the following properties:

Property	Type	Description
timeout	duration	The maximum amount of time that may pass until the execution is cancelled or aborted.
errorOnTimeout (optional)	boolean	`true` if an execution that is aborted due to a timeout should lead to an error (i.e. if the process chain’s status should be set to `ERROR`). `false` if it should just be cancelled (process chain status `CANCELLED`). By default, the execution will be cancelled.

Multiple timeout policies can be combined. For example, a service may be cancelled after 5 minutes of inactivity and aborted with an error if its total execution takes longer than 1 hour.

Example:

YAML
JSON
maxInactivity: 5m
deadline:
  timeout: 1h
  errorOnTimeout: true
{
  "maxInactivity": "5m",
  "deadline": {
    "timeout": "1h",
    "errorOnTimeout": true
  }
}

3.10 Durations

A duration consists of one or more number/unit pairs possibly separated by whitespace characters. Supported units are:

milliseconds, millisecond, millis, milli, ms
seconds, second, secs, sec, s
minutes, minute, mins, min, m
hours, hour, hrs, hr, h
days, day, d

Numbers must be positive integers. The default unit is milliseconds

Examples:

1000ms
3 secs
5m
20mins
10h 30 minutes
1 hour 10minutes 5s
1d 5h
10 days 1hrs 30m 15 secs

3.11 Agents

An agent represents an instance of Steep that can execute process chains.

Property	Type	Description
id (required)	string	A unique agent identifier
available (required)	boolean	`true` if the agent is currently idle and new process chains can be assigned to it, `false` if it is busy executing a process chain
capabilities (required)	array	A set of strings specifying capabilities the agent provides. See also setups.
startTime (required)	string	An ISO 8601 timestamp denoting the date and time when the agent has started.
stateChangedTime (required)	string	An ISO 8601 timestamp denoting the date and time when the value of the `available` property changed from `true` to `false` (i.e. when the agent became busy) or from `false` to `true` (when it became available)
processChainId (optional)	string	The ID of the process chain currently allocated to this agent. May be `null` if no process chain has been allocated to the agent (i.e. if it is currently `available`).

Example:

YAML
JSON
id: akuxryerojbw7mnvovaa
available: true
capabilities:
  - docker
startTime: '2020-05-26T10:50:02.001998Z'
stateChangedTime: '2020-05-26T11:06:52.367121Z'
{
  "id": "akuxryerojbw7mnvovaa",
  "available": true,
  "capabilities": ["docker"],
  "startTime": "2020-05-26T10:50:02.001998Z",
  "stateChangedTime": "2020-05-26T11:06:52.367121Z"
}

3.12 VMs

This data model describes virtual machines created by Steep’s cloud manager.

Property	Type	Description
id (required)	string	A unique VM identifier
externalId (optional)	string	An identifier generated by the Cloud platform
ipAddress (optional)	string	The VM’s IP address
setup (required)	object	The setup used to create this VM
creationTime (optional)	string	An ISO 8601 timestamp denoting the date and time when the VM was created. This property is `null` if the VM has not been created yet.
agentJoinTime (optional)	string	An ISO 8601 timestamp denoting the date and time when a Steep agent has been deployed to the VM and has joined the cluster. This property is `null` if the agent has not joined the cluster yet.
destructionTime (optional)	string	An ISO 8601 timestamp denoting the date and time when the VM was destroyed. This property is `null` if the VM has not been destroyed yet.
status (required)	string	The status of the VM
reason (optional)	string	The reason why the VM has the current status (e.g. an error message if it has the `ERROR` status or a simple message indicating why it has been `DESTROYED`)

3.12.1 VM status

The following table shows the statuses a VM can have:

Status	Description
CREATING	The VM is currently being created
PROVISIONING	The VM has been created and is currently being provisioned (i.e. provisioning scripts defined in the VM’s setup are being executed and the Steep agent is being deployed)
RUNNING	The VM has been created and provisioned successfully. It is currently running and registered as a remote agent.
LEFT	The remote agent on this VM has left. It will be destroyed eventually.
DESTROYING	The VM is currently being destroyed
DESTROYED	The VM has been destroyed
ERROR	The VM could not be created, provisioned, or failed otherwise. See the VM’s `reason` property for more information.

3.13 Setups

A setup describes how a virtual machine (VM) should be created by Steep’s cloud manager.

Property	Type	Description
id (required)	string	A unique setup identifier
flavor (required)	string	The flavor of the new VM
imageName (required)	string	The name of the VM image to deploy
availabilityZone (required)	string	The availability zone in which to create the VM
blockDeviceSizeGb (required)	number	The size of the VM’s main block device in gigabytes
blockDeviceVolumeType (optional)	string	An optional type of the VM’s main block device. By default, the type will be selected automatically.
minVMs (optional)	number	An optional minimum number of VMs to create with this setup. The default value is `0`.
maxVMs (required)	number	The maximum number of VMs to create with this setup
maxCreateConcurrent (optional)	number	The maximum number of VMs to create and provision concurrently. The default value is `1`.
provisioningScripts (optional)	array	An optional list of paths to provisioning scripts that should be executed on the VM after it has been created
providedCapabilities (optional)	array	An optional set of strings specifying capabilities that VMs with this setup will have
sshUsername (optional)	string	An optional username for the SSH connection to the created VM. Overrides the main configuration item `steep.cloud.ssh.username` if it is defined.
additionalVolumes	array	An optional list of volumes that will be attached to the VM

Example:

YAML
JSON
id: default
flavor: 7d217779-4d7b-4689-8a40-c12a377b946d
imageName: Ubuntu 18.04
availabilityZone: nova
blockDeviceSizeGb: 50
minVMs: 0
maxVMs: 4
provisioningScripts:
  - conf/setups/default/01_docker.sh
  - conf/setups/default/02_steep.sh
providedCapabilities:
  - docker
additionalVolumes:
  - sizeGb: 50
    type: SSD
{
  "id": "default",
  "flavor": "7d217779-4d7b-4689-8a40-c12a377b946d",
  "imageName": "Ubuntu 18.04",
  "availabilityZone": "nova",
  "blockDeviceSizeGb": 50,
  "minVMs": 0,
  "maxVMs": 4,
  "provisioningScripts": [
    "conf/setups/default/01_docker.sh",
    "conf/setups/default/02_steep.sh"
  ],
  "providedCapabilities": ["docker"],
  "additionalVolumes": [{
    "sizeGb": 50,
    "type": "SSD"
  }]
}

3.13.1 Volumes

This data model describes an additional volume that can be attached to a virtual machine specified by a setup.

Property	Type	Description
sizeGb (required)	number	The volume’s size in gigabytes
type (optional)	string	Type the volume’s type. By default, the type will be selected automatically.
availabilityZone (optional)	string	The availability zone in which to create the volume. By default, it will be created in the same availability zone as the VM to which it will be attached.

Example:

YAML
JSON
sizeGb: 50
type: SSD
availabilityZone: nova
{
  "sizeGb": 50,
  "type": "SSD",
  "availabilityZone": "nova"
}

3.14 Pool agent parameters

Steep’s cloud manager component is able to create virtual machines and to deploy remote agent instances to it. The cloud manager keeps every remote agent created in a pool. Use pool agent parameters to define a minimum and maximum number of instances per provided capability set.

Property	Type	Description
capabilities (required)	array	A set of strings specifying capabilities that a remote agent must provide so these parameters apply to it
min (optional)	number	An optional minimum number of remote agents that the cloud manager should create with the given capabilities
max (optional)	number	An optional maximum number of remote agents that the cloud manager is allowed to create with the given capabilities

Example:

YAML
JSON
capabilities:
  - docker
  - python
min: 1
max: 5
{
  "capabilities": ["docker", "python"],
  "min": 1,
  "max": 5
}

4 Full-text search

Steep contains a powerful full-text search engine that be used to find submissions and process chains in the backend database. The search engine can be accessed through the /search HTTP endpoint or through the web-based user interface.

4.1 Query language

The focus of Steep’s query language is on the end users. It is lightweight and contains only a few operators. There are no logical combinators such as AND or OR. The main idea is that Steep tries to find as many objects matching the query as possible and then sorts them by relevance so the best matches are on the top of the list. It is assumed that workflows have a higher relevance than process chains. If you are using the search through the web interface, you will typically find what you are looking for on one of the first pages. You rarely have to access any page after the second or third one. This is similar to how a web search engine works.

A search query consists of one or more of the following elements:

Term

A string that should appear somewhere in the document to find.

Put the one or more terms into quotation marks (single or double) if you want to look for exact matches (including spaces). Within quoted terms, quotation marks can be escaped with the backslash character \.

Examples:
docker
"exact match"
"an \"exact match\" with quotation marks"

Date

A string in the form yyyy-MM-dd

The operators < (less than), <= (less than or equal to), > (greater than), and >= (greater than or equal to) can be used to find objects with a date that is before or after the given one.

Examples:
2022-07-17
<2022-07-17
>=2022-07-17

Date/time

A string in the form yyyy-MM-dd'T'HH:mm[:ss]. Seconds are optional.

The operators < (less than), <= (less than or equal to), > (greater than), and >= (greater than or equal to) can be used to find objects with a date/time pair that is before or after the given one.

Examples:
2022-07-17T11:01
2022-07-17T11:01:40
>2022-07-17T11:01
<=2022-07-17T11:01:40

Time range

A string representing a time range in the form yyyy-MM-dd['T'HH:mm[:ss]]..yyyy-MM-dd['T'HH:mm[:ss]]. Times as well as seconds within times are optional. The time range is inclusive, which means that objects with a date that matches the given start date as well as those with a date matching the given end date are included.

Examples:
2022-07-16..2022-07-17
2022-07-17T11:00..2022-07-17T11:01

Locator

A string starting with in: and denoting the attribute that should be compared with the give term(s), dates, date/time pairs, and time ranges. See Attributes below for a complete list of all possible attributes.

Example: in:name

Type

A string starting with is: and denoting the type of documents to search. Possible values are is:workflow and is:processchain.

Filter

A string that consists of an attribute name, followed by a colon and a term, date, date/time pair, or time range that should appear in this attribute. See Attributes below for a complete list of all possible attributes.

Examples:
name:Elvis
start:<=2022-07-17

Attributes

Possible values (including aliases) for attributes are:

id

name

error, errormessage

rc, cap, reqcap, capability, requiredcapability, rcs, caps, reqcaps, capabilities, requiredcapabilities

source

start, startTime

end, endTime

See the submission and process chain data models for more information about these attributes.

4.2 Search examples

filename highmemory

Search for objects that contain the terms filename or highmemory in any of their attributes. Since results are sorted by relevance, objects matching both terms will appear at the top of the list.

"exact match"

Use quotation marks to search for literal (exact) strings.

filename is:workflow

Search for the term filename but only in workflows.

error:127 is:processchain

Search for process chains whose error message contains the term 127.

highmemory in:requiredcapabilities

Search for objects where the term highmemory appears in the list of required capabilities. Does not include objects where the term highmemory appears in any other attribute but the required capabilities.

rcs:highmemory

Search for objects whose required capabilities (alias rcs) contain the term highmemory.

filename status:error

Search for objects containing the term filename but only if their status equals error.

2022-07-17

Search for workflows or process chains that have started or finished on 17 July 2022.

<2022-07-17T11:01

Search for workflows or process chains that have started or finished before 11:01 on 17 July 2022.

>=2022-07-17T11:01:40

Search for workflows or process chains that have started or finished at or after 11:01:40 on 17 July 2022.

start:2022-07-16..2022-07-17

Search for workflows or process chains that have been started between 16 July 2022 and 17 July 2022 (inclusive).

filename in:source is:workflow rcs:highmemory

Search for workflows containing the term filename in their source and whose required capabilities contain the term highmemory.

exit code 127 in:error is:processchain

Search for process chains containing the terms exit, code, or 127 in their error message. Objects containing all terms in their error message will get a higher relevance and appear at the top of the list.

4.3 Search results

The HTTP endpoint /search returns a list of search result objects. Each such object refers to an item found and contains information about which properties of this item have matched with which search term and where in these properties the search term has been found.

The following list describes the properties of this object. For more information about each individual property, please refer to the description of the submission and process chain data models.

Property	Type	Description
id	string	The ID of the found item
type	string	The item’s type. Possible values are `workflow` and `processChain`.
requiredCapabilities	array	The capabilities required for this item to be executed.
status	string	The current status of the item
name (optional)	string	An optional human-readable name (only included if `type` is `workflow` and if the workflow has a name)
startTime (optional)	string	An ISO 8601 timestamp denoting the date and time when the item was started. May be `null` if the execution has not started yet.
endTime (optional)	string	An ISO 8601 timestamp denoting the date and time when the execution of the item has finished. May be `null` if the execution has not finished yet.
matches	array	A list of match objects denoting which properties have matched and what term was found at which location.

Example:

YAML
JSON
id: az2ne7scskxqqzduorzq
type: workflow
requiredCapabilities:
  - sleep
  - docker
status: SUCCESS
name: Docker Sleep
startTime: '2022-06-02T05:43:10.397144Z'
endTime: '2022-06-02T05:43:42.534494Z'
matches:
  - locator: name
    fragment: Docker Sleep
    termMatches:
      - term: docker
        indices:
          - 0
  - locator: requiredCapabilities
    fragment: docker
    termMatches:
      - term: docker
        indices:
          - 0
{
  "id": "az2ne7scskxqqzduorzq",
  "type": "workflow",
  "requiredCapabilities": [
    "sleep",
    "docker"
  ],
  "status": "SUCCESS",
  "name": "Docker Sleep",
  "startTime": "2022-06-02T05:43:10.397144Z",
  "endTime": "2022-06-02T05:43:42.534494Z",
  "matches": [{
    "locator": "name",
    "fragment": "Docker Sleep",
    "termMatches": [{
      "term": "docker",
      "indices": [0]
    }]
  }, {
    "locator": "requiredCapabilities",
    "fragment": "docker",
    "termMatches": [{
      "term": "docker",
      "indices": [0]
    }]
  }]
}

4.4 Matches

A match object specifies a which property of an item has matched with which search term and where the match has occurred.

Property	Type	Description
locator	string	The property in which the match was found. Possible values are `errorMessage`, `id`, `name`, `requiredCapabilities`, `source`, `status`, `startTime`, `endTime`. See the description of the submission and process chain data models for more information about these properties.
fragment	string	A fragment of the property’s value (an ‘excerpt’ or a ‘preview’). If the property’s value is small enough, the fragment might even contain the whole value.
termMatches	array	A list of matches within `fragment` (see below)

termMatches is an array of objects with the following properties:

Property	Type	Description
term	string	The matched term from the search query
indices	array	The start positions (relative to `fragment`) at which the term was found

Example:

YAML
JSON
locator: name
fragment: This is a docker-based service showcasing how docker ...
termMatches:
  - term: docker
    indices:
      - 10
      - 46
{
  "locator": "name",
  "fragment": "This is a docker-based service showcasing how docker ...",
  "termMatches": [{
    "term": "docker",
    "indices": [10, 46]
  }]
}

5 HTTP endpoints

The main way to communicate with Steep (i.e. to submit workflows, to monitor progress, fetch metadata, etc.) is through its HTTP interface. In this section, we describe all HTTP endpoints. By default, Steep listens to incoming connections on port 8080.

5.1 GET information

Get information about Steep. This includes:

Steep’s version number
A build ID
A SHA of the Git commit for which the build was created
A timestamp of the moment when the build was created

Resource URL

Parameters
None

Status codes
200	The operation was successful

Example request

GET / HTTP/1.1

Example response

HTTP/1.1 200 OK
content-encoding: gzip
content-length: 132
content-type: application/json

{
    "build": "1020",
    "commit": "0ed0bc04645b82de523eb7b0dd5f77742e340f5d",
    "timestamp": 1658046958016,
    "version": "6.2.0"
}

5.2 GET health

An endpoint that can be used by external applications at regular intervals to monitor Steep’s health, i.e. to check if it works correctly and if the underlying database as well as all remote agents are reachable.

The response is a JSON object, which will always contain the attribute health. This attribute can be either true if Steep works correctly or false if some error has occurred. Apart from that, the response may contain additional information about data stored in the database (such as the number of submissions) as well as information about remote agents. However, these attributes are not defined and may change in future versions.

Resource URL

/health

Parameters
None

Status codes
200	The operation was successful
503	Service unavailable. Steep may not work as expected.

Example request

GET /health HTTP/1.1

Example response

HTTP/1.1 200 OK
content-encoding: gzip
content-length: 105
content-type: application/json

{
    "agents": {
        "count": 4,
        "health": true
    },
    "health": true,
    "services": {
        "count": 14,
        "health": true
    },
    "submissions": {
        "count": 1960,
        "health": true
    },
    "vms": {
        "count": 4173,
        "health": true
    }
}

5.3 GET submissions

Get information about all submissions in the database. The response is a JSON array consisting of submission objects without the properties workflow, results, and errorMessage. In order to get the complete details of a submission, use the GET submission by ID endpoint.

The submissions are returned in the order in which they were added to the database with the newest ones at the top.

Resource URL

/workflows

Parameters
size (optional)	The maximum number of submissions to return. The default value is 10.
offset (optional)	The offset of the first submission to return. The default value is 0.
status (optional)	If this parameter is defined, Steep will only return submissions with the given status. Otherwise, it will return all submissions from the database. See the list of submission statuses for valid values.

Response headers
x-page-size	The size of the current page (i.e. the maximum number of submission objects returned). See `size` request parameter.
x-page-offset	The offset of the first submission returned. See `offset` request parameter
x-page-total	The total number of submissions in the database matching the given request parameters.

Status codes
200	The operation was successful
400	One of the parameters was invalid. See response body for error message.

Example request

GET /workflows HTTP/1.1

Example response

HTTP/1.1 200 OK
content-encoding: gzip
content-length: 662
content-type: application/json
x-page-offset: 0
x-page-size: 10
x-page-total: 2

[
  {
    "id": "akpm6yojjigral4cdxgq",
    "startTime": "2020-05-18T08:44:01.045710Z",
    "endTime": "2020-05-18T08:44:21.218425Z",
    "status": "SUCCESS",
    "requiredCapabilities": [],
    "runningProcessChains": 0,
    "cancelledProcessChains": 0,
    "succeededProcessChains": 10,
    "failedProcessChains": 0,
    "totalProcessChains": 10
  },
  {
    "id": "akttc5kv575splk3ameq",
    "startTime": "2020-05-24T17:20:37.343072Z",
    "status": "RUNNING",
    "requiredCapabilities": [],
    "runningProcessChains": 1,
    "cancelledProcessChains": 0,
    "succeededProcessChains": 391,
    "failedProcessChains": 0,
    "totalProcessChains": 1000
  }
]

5.4 GET submission by ID

Get details about a single submission from the database.

Resource URL

/workflows/:id

Parameters
id	The ID of the submission to return

Status codes
200	The operation was successful
404	The submssion was not found

Example request

GET /workflows/akpm6yojjigral4cdxgq HTTP/1.1

Example response

HTTP/1.1 200 OK
content-encoding: gzip
content-length: 348
content-type: application/json

{
  "id": "akpm6yojjigral4cdxgq",
  "startTime": "2020-05-18T08:44:01.045710Z",
  "endTime": "2020-05-18T08:44:21.218425Z",
  "status": "SUCCESS",
  "requiredCapabilities": [],
  "runningProcessChains": 0,
  "cancelledProcessChains": 0,
  "succeededProcessChains": 10,
  "failedProcessChains": 0,
  "totalProcessChains": 10,
  "workflow": {
    "api": "4.5.0",
    "vars": [
      …
    ],
    "actions": [
      …
    ]
  }
}

5.5 PUT submission

Update a submission. The request body is a JSON object with the submission properties to update. At the moment, only the status and priority properties can be updated.

If the operation was successful, the response body contains the updated submission without the properties workflow, results, and errorMessage.

Notes:

You can use this endpoint to cancel the execution of a submission (see example below).
If you update a submission’s priority, the priorities of all process chains that belong to this submission and have a status of either REGISTERED or RUNNING will be updated too. Also, all process chains generated from this submission in the future will receive the updated priority. Finished process chains will not be modified.

Resource URL

/workflows/:id

Parameters
id	The ID of the submission to update

Status codes
200	The operation was successful
400	The request body was invalid
404	The submission was not found

Example request

PUT /workflows/akujvtkv575splk3saqa HTTP/1.1
Content-Length: 28
Content-Type: application/json

{
  "status": "CANCELLED"
}

Example response

HTTP/1.1 200 OK
content-encoding: gzip
content-length: 195
content-type: application/json

{
  "id": "akujvtkv575splk3saqa",
  "startTime": "2020-05-25T19:02:21.610396Z",
  "endTime": "2020-05-25T19:02:33.414032Z",
  "status": "CANCELLED",
  "requiredCapabilities": [],
  "runningProcessChains": 0,
  "cancelledProcessChains": 314,
  "succeededProcessChains": 686,
  "failedProcessChains": 0,
  "totalProcessChains": 1000
}

5.6 POST workflow

Create a new submission. The request body contains the workflow to execute.

If the operation was successful, the response body contains submission.

Resource URL

/workflows

Status codes
202	The workflow has been accepted (i.e. stored in the database) and is scheduled for execution.
400	The posted workflow was invalid. See response body for more information.

Example request

POST /workflows HTTP/1.1
Content-Length: 231
Content-Type: application/json

{
  "api": "4.5.0",
  "vars": [{
    "id": "sleep_seconds",
    "value": 3
  }],
  "actions": [{
    "type": "execute",
    "service": "sleep",
    "inputs": [{
      "id": "seconds",
      "var": "sleep_seconds"
    }]
  }]
}

Example response

HTTP/1.1 202 Accepted
content-encoding: gzip
content-length: 374
content-type: application/json

{
  "id": "akukkcsv575splk3v2ma",
  "status": "ACCEPTED",
  "workflow": {
    "api": "4.5.0",
    "vars": [{
      "id": "sleep_seconds",
      "value": 3
    }],
    "actions": [{
      "type": "execute",
      "service": "sleep",
      "inputs": [],
      "outputs": [],
      "inputs": [{
        "id": "seconds",
        "var": "sleep_seconds"
      }]
    }]
  }
}

5.7 GET process chains

Get information about all process chains in the database. The response is a JSON array consisting of process chain objects without the properties executables and results. In order to get the complete details of a process chain, use the GET process chain by ID endpoint.

The process chains are returned in the order in which they were added to the database with the newest ones at the top.

Resource URL

/processchains

Parameters
size (optional)	The maximum number of process chains to return. The default value is 10.
offset (optional)	The offset of the first process chain to return. The default value is 0.
submissionId (optional)	If this parameter is defined, Steep will only return process chains from the submission with the given ID. Otherwise, it will return process chains from all submissions. If there is no submission with the given ID, the result will be an empty array.
status (optional)	If this parameter is defined, Steep will only return process chains with the given status. Otherwise, it will return all process chains from the database. See the list of process chain statuses for valid values.

Response headers
x-page-size	The size of the current page (i.e. the maximum number of process chain objects returned). See `size` request parameter.
x-page-offset	The offset of the first process chain returned. See `offset` request parameter
x-page-total	The total number of process chains in the database matching the given request parameters.

Status codes
200	The operation was successful
400	One of the parameters was invalid. See response body for error message.

Example request

GET /processchains HTTP/1.1

Example response

HTTP/1.1 200 OK
content-encoding: gzip
content-length: 262
content-type: application/json
x-page-offset: 0
x-page-size: 10
x-page-total: 7026

[
  {
    "id": "akukkcsv575splk3v2na",
    "submissionId": "akukkcsv575splk3v2ma",
    "startTime": "2020-05-25T19:46:02.532829Z",
    "endTime": "2020-05-25T19:46:05.546807Z",
    "status": "SUCCESS",
    "requiredCapabilities": []
  },
  {
    "id": "akujvtkv575splk3tppq",
    "submissionId": "akujvtkv575splk3saqa",
    "status": "CANCELLED",
    "requiredCapabilities": []
  },
  …
]

5.8 GET process chain by ID

Get details about a single process chain from the database.

Resource URL

/processchains/:id

Parameters
id	The ID of the process chain to return

Status codes
200	The operation was successful
404	The process chain was not found

Example request

GET /processchains/akukkcsv575splk3v2na HTTP/1.1

Example response

HTTP/1.1 200 OK
content-encoding: gzip
content-length: 535
content-type: application/json

{
  "id": "akukkcsv575splk3v2na",
  "submissionId": "akukkcsv575splk3v2ma",
  "startTime": "2020-05-25T19:46:02.532829Z",
  "endTime": "2020-05-25T19:46:05.546807Z",
  "status": "SUCCESS",
  "requiredCapabilities": [],
  "results": {},
  "executables": [{
    "id": "ayj5kboaxngbglzlxiba",
    "path": "sleep",
    "serviceId": "sleep",
    "runtime": "other",
    "runtimeArgs": [],
    "arguments": [{
      "id": "seconds",
      "type": "input",
      "dataType": "integer",
      "variable": {
        "id": "sleep_seconds",
        "value": "3"
      }
    }]
  }]
}

5.9 GET process chain logs

Get contents of the log file of a process chain.

This endpoint will only return something if process chain logging is enabled in the log configuration. Otherwise, the endpoint will always return HTTP status code 404.

Also note that process chain logs are stored on the machine where the Steep agent that has executed the process chain is running. The log files will only be available as long as the machine exists and the agent is still available. If you want to persist log files use the log configuration and define a location on a shared file system.

This endpoint supports HTTP range requests, which allows you to only fetch a portion of a process chain’s log file.

Resource URL

/logs/processchains/:id

Parameters
id	The ID of the process chain whose log file to return
forceDownload (optional)	`true` if the `Content-Disposition` header should be set in the response. This is useful if you link to a log file from a web page and want the browser to download the file instead of displaying its contents. The default value is `false`.

Request headers
Range (optional)	The part of the log file that should be returned (see HTTP Range header)

Response headers
Accept-Ranges	A marker to advertise support of range requests (see HTTP Accept-Ranges header)
Content-Range (optional)	Indicates what part of the log file is delivered (see HTTP Content-Range header)

Status codes
200	The operation was successful
206	Partial content will be delivered in response to a range request
404	Process chain log file could not be found. Possible reasons: (1) the process chain has not produced any output (yet), (2) the agent that has executed the process chain is not available anymore, (3) process chain logging is disabled in Steep’s configuration
416	Range not satisfiable

Example request

GET /logs/processchains/akukkcsv575splk3v2na HTTP/1.1

Example response

HTTP/1.1 200 OK
content-type: text/plain
accept-ranges: bytes
content-encoding: gzip
transfer-encoding: chunked

2021-03-04 15:34:17 - Hello world!

5.10 HEAD process chain logs

This endpoint can be used to check if a process chain log file exists and how large it is. For more information, please refer to the GET process chain logs endpoint.

Resource URL

/logs/processchains/:id

Parameters
id	The ID of the process chain whose log file to check

Response headers
Content-Length	The total size of the log file
Accept-Ranges	A marker to advertise support of range requests (see HTTP Accept-Ranges header)

Status codes
200	The operation was successful
404	Process chain log file could not be found. Possible reasons: (1) the process chain has not produced any output (yet), (2) the agent that has executed the process chain is not available anymore, (3) process chain logging is disabled in Steep’s configuration

Example request

HEAD /logs/processchains/akukkcsv575splk3v2na HTTP/1.1

Example response

HTTP/1.1 200 OK
content-type: text/plain
content-length: 1291
accept-ranges: bytes

5.11 PUT process chain

Update a process chain. The request body is a JSON object with the process chain properties to update. At the moment, only the status and priority properties can be updated.

If the operation was successful, the response body contains the updated process chain without the properties executables and results.

Notes:

You can use this endpoint to cancel the execution of a process chain (see example below).
The priority can only be modified if the process chain status is REGISTERED or RUNNING. Otherwise, the operation will result in HTTP error 422.

Resource URL

/processchains/:id

Parameters
id	The ID of the process chain to update

Status codes
200	The operation was successful
400	The request body was invalid
404	The process chain was not found
422	The process chain’s priority could not be modified because the process chain is already finished, i.e. the process chain status is not `REGISTERED` or `RUNNING`

Example request

PUT /processchains/akuxzp4rojbw7mnvovcq HTTP/1.1
Content-Length: 28
Content-Type: application/json

{
  "status": "CANCELLED"
}

Example response

HTTP/1.1 200 OK
content-encoding: gzip
content-length: 222
content-type: application/json

{
  "id": "akuxzp4rojbw7mnvovcq",
  "submissionId": "akuxzp4rojbw7mnvovbq",
  "startTime": "2020-05-26T11:06:24.055225Z",
  "endTime": "2020-05-26T11:06:52.367194Z",
  "status": "CANCELLED",
  "requiredCapabilities": []
}

5.12 GET agents

Get information about all agents currently connected to the cluster. In order to get details about a single agent, use the GET agent by ID endpoint.

Resource URL

/agents

Parameters
None

Status codes
200	The operation was successful

Example request

GET /agents HTTP/1.1

Example response

HTTP/1.1 200 OK
content-encoding: gzip
content-length: 195
content-type: application/json

[
  {
    "id": "akuxryerojbw7mnvovaa",
    "available": false,
    "capabilities": [],
    "startTime": "2020-05-26T10:50:02.001998Z",
    "stateChangedTime": "2020-05-26T11:06:52.367121Z"
  },
  {
    "id": "akvn7r3szw5wiztrnotq",
    "available": true,
    "capabilities": [],
    "startTime": "2020-05-27T12:21:24.548640Z",
    "stateChangedTime": "2020-05-27T12:21:24.548640Z"
  }
]

5.13 GET agent by ID

Get details about a single agent.

Resource URL

/agents/:id

Parameters
id	The ID of the agent to return

Status codes
200	The operation was successful
404	The agent was not found

Example request

GET /processchains/akuxryerojbw7mnvovaa HTTP/1.1

Example response

HTTP/1.1 200 OK
content-encoding: gzip
content-length: 177
content-type: application/json

{
  "id": "akuxryerojbw7mnvovaa",
  "available": false,
  "capabilities": [],
  "startTime": "2020-05-26T10:50:02.001998Z",
  "stateChangedTime": "2020-05-26T11:06:52.367121Z"
}

5.14 GET VMs

Get information about all VMs in the database. To get details about a single VM, use the GET VM by ID endpoint.

The VMs are returned in the order in which they were added to the database with the newest ones at the top.

Resource URL

/vms

Parameters
size (optional)	The maximum number of VMs to return. The default value is 10.
offset (optional)	The offset of the first VM to return. The default value is 0.
status (optional)	If this parameter is defined, Steep will only return VMs with the given status. Otherwise, it will return all VMs from the database. See the list of VM statuses for valid values.

Response headers
x-page-size	The size of the current page (i.e. the maximum number of VM objects returned). See `size` request parameter.
x-page-offset	The offset of the first VM returned. See `offset` request parameter
x-page-total	The total number of VMs in the database matching the given request parameters.

Status codes
200	The operation was successful
400	One of the parameters was invalid. See response body for error message.

Example request

GET /vms HTTP/1.1

Example response

HTTP/1.1 200 OK
content-encoding: gzip
content-length: 2402
content-type: application/json
x-page-offset: 0
x-page-size: 10
x-page-total: 614

[
  {
    "id": "akvn5rmvrozqzj5k3n7a",
    "externalId": "cc6bb115-5852-4646-87c0-d61a9e275722",
    "ipAddress": "10.90.5.10",
    "creationTime": "2020-05-27T12:17:01.861596Z",
    "agentJoinTime": "2020-05-27T12:18:27.957192Z",
    "status": "LEFT",
    "setup": {
      "id": "default",
      "flavor": "7d217779-4d7b-4689-8a40-c12a377b946d",
      "imageName": "Ubuntu 18.04",
      "availabilityZone": "nova",
      "blockDeviceSizeGb": 50,
      "minVMs": 0,
      "maxVMs": 4,
      "provisioningScripts": [
        "conf/setups/default/01_docker.sh",
        "conf/setups/default/02_steep.sh"
      ],
      "providedCapabilities": ["docker"]
    }
  },
  {
    "id": "akvnmkuvrozqzj5k3mza",
    "externalId": "f9ecfb9c-d0a1-45c9-87fc-3595bebc85c6",
    "ipAddress": "10.90.5.24",
    "creationTime": "2020-05-27T11:40:19.142991Z",
    "agentJoinTime": "2020-05-27T11:41:42.349354Z",
    "destructionTime": "2020-05-27T11:50:58.961455Z",
    "status": "DESTROYED",
    "reason": "Agent has left the cluster",
    "setup": {
      "id": "default",
      "flavor": "7d217779-4d7b-4689-8a40-c12a377b946d",
      "imageName": "Ubuntu 18.04",
      "availabilityZone": "nova",
      "blockDeviceSizeGb": 50,
      "minVMs": 0,
      "maxVMs": 4,
      "provisioningScripts": [
        "conf/setups/default/01_docker.sh",
        "conf/setups/default/02_steep.sh"
      ],
      "providedCapabilities": ["docker"]
    }
  },
  …
]

5.15 GET VM by ID

Get details about a single VM from the database.

Resource URL

/vms/:id

Parameters
id	The ID of the VM to return

Status codes
200	The operation was successful
404	The VM was not found

Example request

GET /vms/akvn5rmvrozqzj5k3n7a HTTP/1.1

Example response

HTTP/1.1 200 OK
content-encoding: gzip
content-length: 617
content-type: application/json

{
  "id": "akvn5rmvrozqzj5k3n7a",
  "externalId": "cc6bb115-5852-4646-87c0-d61a9e275722",
  "ipAddress": "10.90.5.10",
  "creationTime": "2020-05-27T12:17:01.861596Z",
  "agentJoinTime": "2020-05-27T12:18:27.957192Z",
  "status": "LEFT",
  "setup": {
    "id": "default",
    "flavor": "7d217779-4d7b-4689-8a40-c12a377b946d",
    "imageName": "Ubuntu 18.04",
    "availabilityZone": "nova",
    "blockDeviceSizeGb": 50,
    "minVMs": 0,
    "maxVMs": 4,
    "provisioningScripts": [
      "conf/setups/default/01_docker.sh",
      "conf/setups/default/02_steep.sh"
    ],
    "providedCapabilities": ["docker"]
  }
}

5.16 GET services

Get information about all configured service metadata. To get metadata of a single service, use the GET service by ID endpoint.

Resource URL

/services

Parameters
None

Status codes
200	The operation was successful

Example request

GET /services HTTP/1.1

Example response

HTTP/1.1 200 OK
content-encoding: gzip
content-length: 2167
content-type: application/json

[
  {
    "id": "cp",
    "name": "cp",
    "description": "Copies files",
    "path": "cp",
    "runtime": "other",
    "parameters": [{
      "id": "no_overwrite",
      "name": "No overwrite",
      "description": "Do not overwrite existing file",
      "type": "input",
      "cardinality": "1..1",
      "dataType": "boolean",
      "default": false,
      "label": "-n"
    }, {
      "id": "input_file",
      "name": "Input file name",
      "description": "Input file name",
      "type": "input",
      "cardinality": "1..1",
      "dataType": "file"
    }, {
      "id": "output_file",
      "name": "Output file name",
      "description": "Output file name",
      "type": "output",
      "cardinality": "1..1",
      "dataType": "file"
    }],
    "runtimeArgs": [],
    "requiredCapabilities": []
  }, {
    "id": "sleep",
    "name": "sleep",
    "description": "sleeps for the given amount of seconds",
    "path": "sleep",
    "runtime": "other",
    "parameters": [{
      "id": "seconds",
      "name": "seconds to sleep",
      "description": "The number of seconds to sleep",
      "type": "input",
      "cardinality": "1..1",
      "dataType": "integer"
    }],
    "runtimeArgs": [],
    "requiredCapabilities": []
  },
  …
]

5.17 GET service by ID

Get configured metadata of a single service.

Resource URL

/services/:id

Parameters
id	The ID of the service to return

Status codes
200	The operation was successful
404	The service metadata was not found

Example request

GET /services/sleep HTTP/1.1

Example response

HTTP/1.1 200 OK
content-encoding: gzip
content-length: 401
content-type: application/json

{
  "id": "sleep",
  "name": "sleep",
  "description": "sleeps for the given amount of seconds",
  "path": "sleep",
  "runtime": "other",
  "parameters": [{
    "id": "seconds",
    "name": "seconds to sleep",
    "description": "The number of seconds to sleep",
    "type": "input",
    "cardinality": "1..1",
    "dataType": "integer"
  }],
  "runtimeArgs": [],
  "requiredCapabilities": []
}

5.18 GET search

Perform a full-text search in Steep’s database to find submissions and process chains.

The response is a JSON object with the attributes counts and results:

counts is an object containing the total number of matches in the database for each possible object type (workflow and processChain) as well as a total sum (total). The numbers may either be exact or estimated depending on the count parameter given in the request. The object might also be left off if count equals none.
results is a list of search result objects sorted by relevance.

Resource URL

/search

Parameters
q	The search query
size (optional)	The maximum number of search results to return. The default value is 10.
offset (optional)	The offset of the first search result to return. The default value is 0.
count (optional)	Specifies how Steep should count the total number of search results and if they should be included in the response. Possible values are: `exact` to include an exact count in the response (may take a long time depending on how many objects match), `estimate` to include a rough estimate (very fast but might be incorrect), and `none` if the total number of results should not be counted at all. The default value is `estimate`.
timeZone (optional)	An ID of the time zone in which dates and times in the query are specified (typically the time zone of the client or web browser). Valid values are taken from the IANA Time Zone database (e.g. `Europe/Berlin`). Defaults to the server’s time zone.

Status codes
200	The operation was successful
400	One of the parameters was invalid. See response body for error message.

Example request

GET /search?q=docker HTTP/1.1

Example response

HTTP/1.1 200 OK
content-encoding: gzip
content-length: 886
content-type: application/json
x-page-offset: 0
x-page-size: 10
x-page-total: 10

{
  "counts": {
    "workflow": 6,
    "processChain": 4,
    "total": 10
  },
  "results": [{
    "id": "az2ne7scskxqqzduorzq",
    "type": "workflow",
    "requiredCapabilities": [
      "sleep",
      "docker"
    ],
    "status": "SUCCESS",
    "name": "Docker Sleep",
    "startTime": "2022-06-02T05:43:10.397144Z",
    "endTime": "2022-06-02T05:43:42.534494Z",
    "matches": [{
      "locator": "name",
      "fragment": "Docker Sleep",
      "termMatches": [{
        "term": "docker",
        "indices": [0]
      }]
    }, {
      "locator": "requiredCapabilities",
      "fragment": "docker",
      "termMatches": [{
        "term": "docker",
        "indices": [0]
      }]
    }]
  },
  ...
  ]
}

5.19 GET Prometheus metrics

Steep can provide metrics to Prometheus. Besides statistics about the Java Virtual Machine that Steep is running in, the following metrics are included:

Metric	Description
`steep_remote_agents`	The number of registered remote agents
`steep_controller_process_chains`	The number of generated process chains the controller is currently waiting for grouped by `submissionId`
`steep_scheduler_process_chains`	The number of process chains with a given status (indicated by the label `status`)
`steep_local_agent_retries`	The total number of times an executable with a given service ID (indicated by the label `serviceId`) had to be retried
`steep_eventbus_compressedjson_messages`	Total number of compressed JSON messages sent/received over the event bus (label `operation` is either `sent` or `recv`)
`steep_eventbus_compressedjson_bytes`	Total number of compressed JSON bytes. Label `operation` is either `sent` or `recv`, and label `stage` is either `compressed` or `uncompressed`. Uncompressed bytes will be compressed before they are sent over the event bus, and received compressed bytes will be uncompressed.
`steep_eventbus_compressedjson_time`	Total number of milliseconds spent compressing or decompressing JSON (label `operation` is either `sent` or `recv` and specifies if sent bytes have been compressed or received bytes have been uncompressed)

Resource URL

/metrics

Parameters
None

Status codes
200	The operation was successful

Example request

GET /metrics HTTP/1.1

Example response

HTTP/1.1 200 OK
content-type: text/plain
content-encoding: gzip
content-length: 1674

# HELP jvm_memory_bytes_used Used bytes of a given JVM memory area.
# TYPE jvm_memory_bytes_used gauge
jvm_memory_bytes_used{area="heap",} 2.1695392E8
jvm_memory_bytes_used{area="nonheap",} 1.46509968E8
…
# HELP steep_remote_agents Number of registered remote agents
# TYPE steep_remote_agents gauge
steep_remote_agents 1.0
…
# HELP steep_scheduler_process_chains Number of process chains with a given status
# TYPE steep_scheduler_process_chains gauge
steep_scheduler_process_chains{status="SUCCESS",} 2.0
steep_scheduler_process_chains{status="RUNNING",} 0.0
steep_scheduler_process_chains{status="ERROR",} 1.0
…

6 Web-based user interface

Steep has a web-based user interface that allows you to monitor the execution of running workflows, process chains, agents, and VMS, as well as to browse the database contents.

Start Steep and visit any of the above-mentioned HTTP endpoints with your web browser to open the user interface.

7 Configuration

After you have downloaded and extracted Steep, you can find its configuration files under the conf directory. The following sections describe each of these files in detail.

7.1 steep.yaml

The file steep.yaml contains the main configuration of Steep. In this section, we describe all configuration keys and values you can set.

Note that keys are specified using the dot notation. You can use them as they are given here or use YAML notation instead. For example, the following configuration item

steep.cluster.eventBus.publicPort: 41187

is identical to:

steep:
  cluster:
    eventBus:
      publicPort: 41187

You may override items in your configuration file with environment variables. This is particularly useful if you are using Steep inside a Docker container. The environment variables use a slightly different naming scheme. All variables are in capital letters and dots are replaced by underscores. For example, the configuration key steep.http.host becomes STEEP_HTTP_HOST and steep.cluster.eventBus.publicPort becomes STEEP_CLUSTER_EVENTBUS_PUBLICPORT. You may use YAML syntax to specify environment variable values. For example, the array steep.agent.capabilities can be specified as follows:

STEEP_AGENT_CAPABILITIES=["docker", "python"]

7.1.1 General configuration

steep.tmpPath

The path to a directory where temporary files should be stored during processing. Steep generates names for the outputs of execute actions in a workflow. If the store flag of an output parameter is false (which is the default), the generated filename will be relative to this temporary directory.

steep.outPath

The path to a directory where output files should be stored. This path will be used instead of steep.tmpPath to generate a filename for an output parameter if its store flag is true.

steep.overrideConfigFile

The path to a file that keeps additional configuration. The values of the overrideConfigFile will be merged into the main configuration file, so it basically overrides the default values. Note that configuration items in this file can still be overridden with environment variables. This configuration item is useful if you don’t want to change the main configuration file (or if you cannot do so) but still want to set different configuration values. Use it if you run Steep in a Docker container and bind mount the overrideConfigFile as a volume.

steep.services

The path to the configuration files containing service metadata. Either a string pointing to a single file, a glob pattern (e.g. **/*.yaml), or an array of files or glob patterns.

steep.plugins

The path to the configuration file(s) containing plugin descriptors. Either a string pointing to a single file, a glob pattern (e.g. **/*.yaml), or an array of files or glob patterns.

7.1.2 Cluster settings

Use these configuration items to build up a cluster of Steep instances. Under the hood, Steep uses Vert.x and Hazelcast, so these configuration items are very similar to the ones found in these two frameworks. To build up a cluster, you need to configure an event bus connection and a cluster connection. They should use different ports. host typically refers to the machine your instance is running on and publicHost or publicAddress specify the hostname or IP address that your Steep instance will use in your network to advertise itself so that other instances can connect to it.

For more information, please read the documentation of Vert.x and Hazelcast.

steep.cluster.eventBus.host

The IP address (or hostname) to bind the clustered eventbus to

Default: Automatically detected local network interface

steep.cluster.eventBus.port

The port the clustered eventbus should listen on

Default: A random port

steep.cluster.eventBus.publicHost

The IP address (or hostname) the eventbus uses to announce itself within in the cluster

Default: Same as steep.cluster.eventBus.host

steep.cluster.eventBus.publicPort

The port that the eventbus uses to announce itself within in the cluster

Default: Same as steep.cluster.eventBus.port

steep.cluster.hazelcast.clusterName

An optional cluster name that can be used to separate clusters of Steep instances. Two instances from different clusters (with different names) cannot connect to each other.

By default, no cluster name is set, which means all instances can connect to each other. However, a Steep instance without a cluster name cannot connect to a named cluster.

Heads up: if you have a cluster name set and you’re using a cloud connection to deploy remote agents on demand, make sure these Steep instances use the same cluster name. Otherwise, you won’t be able to connect to them.

steep.cluster.hazelcast.publicAddress

The IP address (or hostname) and port Hazelcast uses to announce itself within in the cluster

steep.cluster.hazelcast.port

The port that Hazelcast should listen on

steep.cluster.hazelcast.interfaces

A list of IP address patterns specifying valid interfaces Hazelcast should bind to

steep.cluster.hazelcast.members

A list of IP addresses (or hostnames) of Hazelcast cluster members

steep.cluster.hazelcast.tcpEnabled

true if Hazelcast should use TCP to connect to other instances, false if it should use multicast

Default: false

steep.cluster.hazelcast.restoreMembersOnStartup.enabled

true if Steep should try to load IP addresses of possibly still running VMs from its database during startup and add them to steep.cluster.hazelcast.members. This is useful if a Steep instance has crashed and should be reintegrated into an existing cluster when it’s back.

Default: false

steep.cluster.hazelcast.restoreMembersOnStartup.defaultPort

If steep.cluster.hazelcast.restoreMembersOnStartup.enabled is true, potential Hazelcast cluster members will be restored from database. This configuration item specifies on which Hazelcast port these members are listening.

steep.cluster.hazelcast.placementGroupName

An optional name specifying in which group this Hazelcast member should be placed. Steep uses distributed maps to share data between instances. Data in these maps is partitioned (i.e. distributed to the individual cluster members). In a large cluster, no member keeps all the data. Most nodes only keep a small fraction of the data (a partition).

To make sure data is not lost if a member goes down, Hazelcast uses backups to distribute copies of the data across the cluster. By specifying a placement group, you can control how Hazelcast distributes these backups. Hazelcast will always prefer creating backups in a group that does not own the data so that if all members of a group go down, the other group still has all the backup data.

Examples for sensible groups are racks, data centers, or availability zones.

For more information, see the following links:

https://docs.hazelcast.com/hazelcast/5.1/architecture/data-partitioning

https://docs.hazelcast.com/hazelcast/5.1/clusters/partition-group-configuration

https://docs.hazelcast.com/hazelcast/5.1/data-structures/backing-up-maps

Note that if you configure a placement group name, all members in your cluster must also have a placement group name. Otherwise, you will receive an exception about mismatching configuration on startup.

steep.cluster.hazelcast.liteMember

true if this instance should be a Hazelcast lite member. Lite members do not own any in-memory data. They are mainly used for compute-intensive tasks. With regard to Steep, an instance with a controller and a scheduler should not be a lite member, because these components heavily rely on internal state. A Steep instance that only contains an agent and therefore only executes services, however, could be a lite member. See the architecture section for more information about these components.

Your cluster cannot consist of only lite members. Otherwise, it is not able to maintain internal state at all.

Note that since lite members cannot keep data, they are not suitable to keep backups either. See steep.cluster.hazelcast.placementGroupName for more information. For reasons of reliability, a cluster should contain at least three full (i.e. non-lite) members.

steep.cluster.lookupOrphansInterval

The interval at which Steep’s main thread looks for orphaned entries in its internal remote agent registry (specified as a duration). Such entries may (very rarely) happen if there is a network failure during deregistration of an agent. You normally do not have to change this configuration.

Default: 5m

7.1.3 HTTP configuration

steep.http.enabled

true if the HTTP interface should be enabled

Default: true

steep.http.host

The host to bind the HTTP server to

Default: localhost

steep.http.port

The port the HTTP server should listen on

Default: 8080

steep.http.postMaxSize

The maximum size of HTTP POST bodies in bytes

Default: 1048576 (1 MB)

steep.http.basePath

The path where the HTTP endpoints and the web-based user interface should be mounted

Default: "" (empty string, i.e. no base path)

steep.http.cors.enable

true if Cross-Origin Resource Sharing (CORS) should be enabled

Default: false

steep.http.cors.allowOrigin

A regular expression specifying allowed CORS origins. Use * to allow all origins.

Default: "$." (match nothing by default)

steep.http.cors.allowCredentials

true if the Access-Control-Allow-Credentials response header should be returned.

Default: false

steep.http.cors.allowHeaders

A string or an array indicating which header field names can be used in a request.

steep.http.cors.allowMethods

A string or an array indicating which HTTP methods can be used in a request.

steep.http.cors.exposeHeaders

A string or an array indicating which headers are safe to expose to the API of a CORS API specification.

steep.http.cors.maxAgeSeconds

The number of seconds the results of a preflight request can be cached in a preflight result cache.

7.1.4 Controller configuration

steep.controller.enabled

true if the controller should be enabled. Set this value to false if your Steep instance does not have access to the shared database.

Default: true

steep.controller.lookupInterval

The interval at which the controller looks for accepted submissions, specified as a duration.

Default: 2s

steep.controller.lookupMaxErrors

The maximum number of consecutive errors (e.g. database connection issues) to tolerate when looking up the status of process chains of a running submission. If there are more errors, the submission will be aborted.

Default: 5

steep.controller.lookupOrphansInterval

The interval at which the controller looks for orphaned running submissions (i.e. submissions that are in the status RUNNING but that are currently not being processed by any controller instance), specified as a duration. If Steep finds such a submission it will try to resume it.

Default: 5m

steep.controller.lookupOrphansInitialDelay

The time the controller should wait after startup before it looks for orphaned running submissions for the first time (specified as a duration). This property is useful if you want to implement a rolling update from one Steep instance to another.

Default: 0s

7.1.5 Scheduler configuration

steep.scheduler.enabled

true if the scheduler should be enabled. Set this value to false if your Steep instance does not have access to the shared database.

Default: true

steep.scheduler.lookupInterval

The interval at which the scheduler looks for registered process chains, specified as a duration.

Default: 20s

steep.scheduler.lookupOrphansInterval

The interval at which the scheduler looks for orphaned running process chains (i.e. process chains that are in the status RUNNING but that are currently not being processed by any scheduler instance), specified as a duration. Note that the scheduler also always looks for orphaned process chains when it detects that another scheduler instance has just left the cluster (regardless of the configured interval).

Default: 5m

steep.scheduler.lookupOrphansInitialDelay

The time the scheduler should wait after startup before it looks for orphaned running process chains for the first time (specified as a duration). This property is useful if you want to implement a rolling update from one Steep instance to another. Note that the scheduler also looks for orphaned process chains when another scheduler instance has just left the cluster, even if the initial delay has not passed by yet.

Default: 0s

7.1.6 Agent configuration

steep.agent.enabled

true if this Steep instance should be able to execute process chains (i.e. if one or more agents should be deployed)

Default: true

steep.agent.instances

The number of agents that should be deployed within this Steep instance (i.e. how many executables the Steep instance can run in parallel)

Default: 1

steep.agent.id

Unique identifier for the first agent instance deployed. Subsequent agent instances will have a consecutive number appended to their IDs.

Default: (an automatically generated unique ID)

steep.agent.capabilities

List of capabilities that the agents provide

Default: [] (empty list)

steep.agent.autoShutdownTimeout

The time any agent instance can remain idle until Steep shuts itself down gracefully (specified as a duration). By default, this value is 0s, which means Steep never shuts itself down.

Default: 0s

steep.agent.busyTimeout

The time that should pass before an idle agent decides that it is not busy anymore (specified as a duration). Normally, the scheduler allocates an agent, sends it a process chain, and then deallocates it after the process chain execution has finished. This value is important if the scheduler crashes while the process chain is being executed and does not deallocate the agent anymore. In this case, the agent deallocates itself after the configured time has passed.

Default: 1m

steep.agent.outputLinesToCollect

The number of output lines to collect at most from each executed service (also applies to error output)

Default: 100

7.1.7 Runtime settings

steep.runtimes.docker.env

Additional environment variables that will be passed to containers created by the Docker runtime

Example: ["key=value", "foo=bar"]

Default: [] (empty list)

steep.runtimes.docker.volumes

Additional volume mounts to be passed to the Docker runtime

Example: ["/data:/data"]

Default: [] (empty list)

7.1.8 Database connection

steep.db.driver

The database driver

Valid values: inmemory, postgresql, mongodb

Default: inmemory

steep.db.url

The database URL

steep.db.username

The database username (only used by the postgresql driver)

steep.db.password

The database password (only used by the postgresql driver)

steep.db.connectionPool.maxSize

The maximum number of connections to keep open (i.e. to keep in the connection pool)

steep.db.connectionPool.maxIdleTime

The maximum time an idle connection should be kept in the connection pool before it is closed

7.1.9 Cloud connection

steep.cloud.enabled

true if Steep should connect to a cloud to acquire remote agents on demand

Default: false

steep.cloud.driver

Defines which cloud driver to use

Valid values: openstack (see the OpenStack cloud driver for more information)

steep.cloud.createdByTag

A metadata tag that should be attached to virtual machines to indicate that they have been created by Steep

steep.cloud.setupsFile

The path to the file that describes all available setups. See setups.yaml.

steep.cloud.syncInterval

The time that should pass before the cloud manager synchronizes its internal state with the cloud again, specified as a duration.

Default: 2m

steep.cloud.keepAliveInterval

The time that should pass before the cloud manager sends keep-alive messages to a minimum of remote agents again (so that they do not shut down themselves), specified as a duration. See minVMs property of the setups data model.

Default: 30s

steep.cloud.timeouts.sshReady

The maximum time the cloud manager should try to log in to a new VM via SSH (specified as a duration). The cloud manager will make a login attempt every 2 seconds until it is successful or until the maximum number of seconds have passed, in which case it will destroy the VM.

Default: 5m

steep.cloud.timeouts.agentReady

The maximum time the cloud manager should wait for an agent on a new VM to become available (i.e. how long a new Steep instance may take to register with the cluster) before it destroys the VM again (specified as a duration).

Default: 5m

steep.cloud.timeouts.createVM

The maximum time that creating a VM may take before it is aborted with an error (specified as a duration).

Default: 5m

steep.cloud.timeouts.destroyVM

The maximum time that destroying a VM may take before it is aborted with an error (specified as a duration).

Default: 5m

steep.cloud.agentPool

An array of agent pool parameters describing how many remote agents the cloud manager should keep in its pool how many it is allowed to create for each given set of capabilities.

Default: [] (empty list)

7.1.10 OpenStack cloud driver

steep.cloud.openstack.endpoint

OpenStack authentication endpoint

steep.cloud.openstack.username

OpenStack username used for authentication

steep.cloud.openstack.password

OpenStack password used for authentication

steep.cloud.openstack.domainName

OpenStack domain name used for authentication

steep.cloud.openstack.projectId

The ID of the OpenStack project to which to connect. Either this configuration item or steep.cloud.openstack.projectName must be set but not both at the same time.

steep.cloud.openstack.projectName

The name of the OpenStack project to which to connect. This configuration item will be used in combination with steep.cloud.openstack.domainName if steep.cloud.openstack.projectId is not set.

steep.cloud.openstack.networkId

The ID of the OpenStack network to attach new VMs to

steep.cloud.openstack.usePublicIp

true if new VMs should have a public IP address

Default: false

steep.cloud.openstack.securityGroups

The OpenStack security groups that should be attached to new VMs.

Default: [] (empty list)

steep.cloud.openstack.keypairName

The name of the keypair to deploy to new VMs. The keypair must already exist in OpenStack.

7.1.11 SSH connection to VMs

steep.cloud.ssh.username

Username for SSH access to VMs. Can be overriden by the sshUsername property in each setup. May even be null if all setups define their own username.

steep.cloud.ssh.privateKeyLocation

Location of a private key to use for SSH

7.1.12 Log configuration

steep.logs.level

The default log level for all loggers (console as well as file-based)

Valid values: TRACE, DEBUG, INFO, WARN, ERROR, OFF.

Default: DEBUG

steep.logs.main.enabled

true if logging to the main log file should be enabled

Default: false

steep.logs.main.logFile

The name of the main log file

Default: logs/steep.log

steep.logs.main.dailyRollover.enabled

true if main log files should be renamed every day. The file name will be based on steep.logs.main.logFile and the file’s date in the form YYYY-MM-DD (e.g. steep.2020-11-19.log)

Default: true

steep.logs.main.dailyRollover.maxDays

The maximum number of days’ worth of main log files to keep

Default: 7

steep.logs.main.dailyRollover.maxSize

The total maximum size of all main log files in bytes. Oldest log files will deleted when this size is reached.

Default: 104857600 (100 MB)

steep.logs.processChains.enabled

true if the output of process chains should be logged separately to disk. The output will still also appear on the console and in the main log file (if enabled), but there, it’s not separated by process chain. This feature is useful if you want to record the output of individual process chains and make it available through the process chain logs endpoint.

Default: false

steep.logs.processChains.path

The path where process chain logs will be stored. Individual files will will be named after the ID of the corresponding process chain (e.g. aprsqz6d5f4aiwsdzbsq.log).

Default: logs/processchains

steep.logs.processChains.groupByPrefix

Set this configuration item to a value greater than 0 to group process chain log files by prefix in subdirectories under the directory configured through steep.logs.processChains.path. For example, if this configuration item is set to 3, Steep will create a separate subdirectory for all process chains whose ID starts with the same three characters. The name of this subdirectory will be these three characters. The process chains apomaokjbk3dmqovemwa and apomaokjbk3dmqovemsq will be put into a subdirectory called apo, and the process chain ao344a53oyoqwhdelmna will be put into ao3. Note that in practice, 3 is a reasonable value, which will create a new directory about every day. A value of 0 disables grouping.

Default: 0

7.1.13 Garbage collector configuration

steep.garbageCollector.enabled

true if the garbage collector should be enabled. The garbage collector runs in the background and removes outdated objects from the database at the interval specified with steep.garbageCollector.cron

Default: false

steep.garbageCollector.cron

A UNIX-like cron expression specifying the interval at which the garbage collector should be executed. Cron expressions consist of six required fields and one optional field separated by a white space:

SECONDS MINUTES HOURS DAY-OF-MONTH MONTH DAY-OF-WEEK [YEAR].

Use an asterisk * to specify all values (e.g. every second or every minute). Use a question mark ? for DAY-OF-MONTH or DAY-OF-WEEK to specify no value (only one of DAY-OF-MONTH or DAY-OF-WEEK can be specified at the same time). Use a slash / to specify increments (e.g. */5 for every 5 minutes).

More information about the format can be found in the javadoc of the org.quartz.CronExpression class.

Example: 0 0 0 * * ? (daily at 12am)

steep.garbageCollector.retention.submissions

The maximum time a submission should be kept in the database after it has finished (regardless of whether it was successful or not). The time can be specified as a human-readable duration.

Default: null (submissions will be kept indefinitely)

steep.garbageCollector.retention.vms

The maximum time a VM should be kept in the database after it has been destroyed (regardless of its status). The time can be specified as a human-readable duration.

Default: null (VMs will be kept indefinitely)

7.1.14 Cache configuration

steep.cache.plugins.enabled

true if the persistent compiled plugin cache should be enabled. Steep updates this cache on startup when it has first compiled a plugin script or when it detects that a previously compiled script has changed. On subsequent startups, Steep can utilize the cache to skip compilation of known plugins and, therefore, to reduce startup time.

Default: false

steep.cache.plugins.path

The path to a directory where Steep should store compiled plugin scripts if the persistent compiled plugin cache is enabled (see steep.cache.plugins.enabled).

Default: .cache/plugins

7.2 setups.yaml

The configuration file setups.yaml contains an array of setup objects that Steep’s cloud manager component uses to create new virtual machines and to deploy remote agents to it.

7.3 services/services.yaml

The file services/services.yaml contains an array of service metadata objects describing the interfaces of all processing services Steep can execute.

7.4 plugins/common.yaml

The configuration file plugins/common.yaml describes all plugins so Steep can compile and use them during runtime. The file contains an array of descriptor objects with the properties specified in the section on extending Steep through plugins.

7.5 Advanced configuration topics

7.5.1 Provisioning scripts

After Steep’s cloud manager has created a VM, it uploads the provisioning scripts defined in the corresponding setup to the VM and executes them. The scripts can be used to deploy software to the VM and to make sure all required services (including Steep) are running.

Each provisioning script is a simple executable script file with a valid UNIX shebang at the beginning.

Script files will be processed by a template engine before they are uploaded. The following sections describe supported template instructions.

7.5.1.1 Environment variables

Access any environment variable defined on the system where Steep is running (not the VM to be provisioned) as follows:

{{ env["name_of_the_environment_variable"] }}

Example provisioning script

#!/usr/bin/env bash

echo "{{ env["TOKEN"] }}" > /etc/token.conf

7.5.1.2 Configuration values

Use values from Steep’s main configuration file (steep.yaml) as follows:

{{ config["name_of_the_configuration_item"] }}

Example provisioning script

#!/usr/bin/env bash

docker run -u root -d -p 5701:5701 -p 41187:41187 \
  --restart=on-failure --name steep \
  -e "STEEP_OUTPATH={{ config["steep.outPath"] }}" \
  -e "STEEP_TMPPATH={{ config["steep.tmpPath"] }}" \
  steep:latest

7.5.1.3 Read local files

Insert the contents of a local file into the provisioning script.

{{ readFile("path_to_the_file_to_insert") }}

Example provisioning script

#!/usr/bin/env bash

echo "{{ readFile("hello_world.txt") }}"

7.5.1.4 Upload local files to remote

Upload one or more local files to the remote VM.

{{ upload("source", "destination") }}

source may contain a glob pattern (e.g. *.sh or **/*.yaml) if you want to upload multiple files or if you want to recursively transfer a whole directory tree. In this case, destination should be a directory and it should exist.

Example provisioning script

#!/usr/bin/env bash

mkdir -p /etc/steep
{{ upload("conf/**/*.yaml", "/etc/steep") }}

7.5.2 Using YAML anchors

Configuration files for setups (setups.yaml) and service metadata (services/services.yaml) often contain repeated information (e.g. two setups might offer the same capabilities). You can use YAML anchors to simplify your configuration files.

The following example shows two services sharing a parameter:

- id: sleep
  name: sleep
  description: sleeps for the given amount of seconds
  path: sleep
  runtime: other

  parameters:
    - &sleep_seconds
      id: seconds
      name: seconds to sleep
      description: The number of seconds to sleep
      type: input
      cardinality: 1..1
      dataType: integer

- id: docker_sleep
  name: Docker sleep
  description: Run sleep inside an alpine container
  path: alpine
  runtime: docker

  parameters:
    - id: sleep
      name: sleep command
      description: The sleep command
      type: input
      cardinality: 1..1
      dataType: string
      default: sleep

    - *sleep_seconds

7.5.3 Using a template engine

You can use a template engine in all of Steep’s YAML-based configuration files (steep.yaml, setups.yaml, services.yaml, etc.) to dynamically generate a configuration at startup.

You have to explicitly enable this feature by adding front matter to your YAML file and setting the attribute template to true:

---
template: true
---

Steep uses Pebble Templates to compile your configuration files. Please refer to their website for a full documentation on the tags, functions, and filters you can use.

Within your template, you may access the following variables:

Variable	Description
`env`	A dictionary of environment variables. Use subscript notation (`[]`) to access its contents. Example: `{{ env["PATH"] }}`
`config`	A dictionary of configuration properties. This variable is not available in `steep.yaml` (or any override configuration file). Use subscript notation (`[]`) to access its contents. Example: `{{ config["steep.cluster.hazelcast.publicAddress"] }}`

Here is a full example of a setups.yaml file that uses the templating feature to create two setups with the same parameters, an image name from an environment variable, but different availability zones:

---
template: true
---

{% for az in ["us-east-1", "eu-central-1"] %}
- id: my_setup_{{ az }}
  flavor: m4.2xlarge
  availabilityZone: {{ az }}
  imageName: {{ env["MY_SETUP_IMAGE_NAME"] }
  blockDeviceSizeGb: 50
  minVMs: 0
  maxVMs: 10
{% endfor %}

8 Extending Steep through plugins

Steep can be extended through plugins. In this section, we will describe the interfaces of all plugins and how they need to be configured so Steep can compile and execute them at runtime.

Each plugin is a Kotlin script with the file extension .kt or .kts. Inside this script, there should be a single function with the same name as the plugin and a signature that depends on the plugin type. Function interfaces are described in the sub-sections below.

All plugins must be referenced in the plugins/common.yaml file. This file is an array of descriptor objects with at least the following properties:

Property	Type	Description
name (required)	string	A unique name of the plugin (the function inside the plugin’s script file must have the same name)
type (required)	string	The plugin type. Valid values are: `initializer`, `outputAdapter`, `processChainAdapter`, `processChainConsistencyChecker`, and `runtime`.
scriptFile (required)	string	The path to the plugin’s Kotlin script file. The file should have the extension `.kt` or `.kts`. The path is relative to Steep’s application directory, so a valid example is `conf/plugins/fileOrEmptyList.kt`.
version (optional)	string	The plugin’s version. Must follow the Semantic Versioning Specification.

Specific plugin types may require additional properties described in the sub-sections below.

Plugins are compiled on demand when Steep is starting. This can take some time depending on the number of the plugins and their size. For faster start times, you can configure a persistent compiled plugin cache. Steep updates this cache on startup when it has first compiled a script or when it detects that a previously compiled script has changed. On subsequent startups, Steep can utilize the cache to skip compilation of known plugins and, therefore, to reduce startup time.

8.1 Initializers

An initializer plugin is a function that will be called during the initialization phase of Steep just before components such as the controller or the scheduler are deployed. If required, the function can be a suspend function.

Type

initializer

Additional properties	Type
dependsOn (optional)	array	An optional list of names of other initializer plugins that need to be executed before this plugin. If this property is not given, the order in which initializer plugins are executed is undefined.

Function interface

suspend fun myInitializer(vertx: io.vertx.core.Vertx)

Example descriptor

- name: myInitializer
  type: initializer
  scriptFile: conf/plugins/myInitializer.kt

Example plugin script

suspend fun myInitializer(vertx: io.vertx.core.Vertx) {
  println("Hello from my initializer plugin")
}

8.2 Output adapters

An output adapter plugin is a function that can manipulate the output of services depending on their produced data type (see the dataType property of the service parameter data model, as well as the dataType property of the process chain argument data model).

In other words, if an output parameter of a processing service has a specific dataType defined in the service’s metadata and this data type matches the one given in the output adapter’s descriptor, then the plugin’s function will be called after the service has been executed. Steep will pass the output argument and the whole process chain (for reference) to the plugin. The output argument’s value will be the current result (i.e. the output file or directory). The plugin can modify this file or directory (if necessary) and return a new list of files that will then be used by Steep for further processing.

Steep has a built-in output adapter for the data type directory. Whenever you specify this data type in the service metadata, Steep will pass the output directory to an internal function that recursively collects all files from this directory and returns them as a list.

The example output adapter fileOrEmptyList described below is also included in Steep. It checks if an output file exists (i.e. if the processing service has actually created it) and either returns a list with a single element (the file) or an empty list. This is useful if a processing service has an optional output that you want to use as input of a subsequent for-each action or of the current for-each action via yieldToInput.

If required, the function can be a suspend function.

Type

outputAdapter

Additional properties	Type
supportedDataType (required)	string	The `dataType` that this plugin can handle

Function interface

suspend fun myOutputAdapter(output: model.processchain.Argument,
  processChain: model.processchain.ProcessChain,
  vertx: io.vertx.core.Vertx): List<Any>

Example descriptor

- name: fileOrEmptyList
  type: outputAdapter
  scriptFile: conf/plugins/fileOrEmptyList.kt
  supportedDataType: fileOrEmptyList

Example plugin script

import io.vertx.core.Vertx
import io.vertx.kotlin.core.file.existsAwait
import model.processchain.Argument
import model.processchain.ProcessChain

suspend fun fileOrEmptyList(output: Argument, processChain: ProcessChain,
    vertx: Vertx): List<String> {
  return if (!vertx.fileSystem().existsAwait(output.variable.value)) {
    emptyList()
  } else {
    listOf(output.variable.value)
  }
}

8.3 Process chain adapters

A process chain adapter plugin is a function that can manipulate generated process chains before they are executed.

It takes a list of generated process chains and a reference to the workflow from which the process chains have been generated. It returns a new list of process chains to execute or the given list if no modification was made. If required, the function can be a suspend function.

Type

processChainAdapter

Additional properties	Type
dependsOn (optional)	array	An optional list of names of other process chain adapter plugins that need to be executed before this plugin. If this property is not given, the order in which process chain adapter plugins are applied to process chains is undefined.

Function interface

suspend fun myProcessChainAdapter(processChains: List<model.processchain.ProcessChain>,
  workflow: model.workflow.Workflow, vertx: io.vertx.core.Vertx): List<model.processchain.ProcessChain>

Example descriptor

- name: myProcessChainAdapter
  type: processChainAdapter
  scriptFile: conf/plugins/myProcessChainAdapter.kt

Example plugin script

import model.processchain.ProcessChain
import model.workflow.Workflow
import io.vertx.core.Vertx

suspend fun myProcessChainAdapter(processChains: List<ProcessChain>,
    workflow: Workflow, vertx: Vertx): List<ProcessChain> {
  val result = mutableListOf<ProcessChain>()

  for (pc in processChains) {
    // never execute the 'sleep' service
    val executables = pc.executables.filter { e -> e.id != "sleep" }
    result.add(pc.copy(executables = executables))
  }

  return result
}

8.4 Process chain consistency checkers

A process chain consistency checker plugin is a function that checks if an execute action can be added to a process chain or if adding it would lead to inconsistencies that render the process chain inexecutable.

The function is called before the execute action is converted to an executable and before it is added to the process chain. It takes a list of executables that have been collected so far during process chain generation, the execute action that is about to be converted, the workflow from which the process chain is being created, and a Vert.x instance.

It returns true if the execute action can safely be converted and added to the list of executables to make up a new process chain, or false if adding it would lead to a process chain that could not be executed later.

Steep will not discard actions that a consistency checker plugin has rejected. Instead, it will try to add them to another process chain later. At this point, the plugin will be called again.

If required, the function can be a suspend function.

Type

processChainConsistencyChecker

Additional properties	Type
dependsOn (optional)	array	An optional list of names of other process chain consistency checker plugins that need to be executed before this plugin. If this property is not given, the order in which consistency checkers are applied to process chains is undefined.

Function interface

suspend fun myProcessChainConsistencyChecker(processChain: List<model.processchain.Executable>,
  action: model.workflow.ExecuteAction, workflow: model.workflow.Workflow,
  vertx: io.vertx.core.Vertx): Boolean

Example descriptor

- name: myProcessChainConsistencyChecker
  type: processChainConsistencyChecker
  scriptFile: conf/plugins/myProcessChainConsistencyChecker.kt

Example plugin script

import io.vertx.core.Vertx
import model.processchain.Executable
import model.workflow.ExecuteAction
import model.workflow.Workflow

fun dummyProcessChainConsistencyChecker(processChain: List<Executable>,
    action: ExecuteAction, workflow: Workflow, vertx: Vertx): Boolean {
  // do not add a service more than once to a process chain
  return processChain.none { it.serviceId == action.service }
}

8.5 Custom runtime environments

A runtime plugin is a function that can run process chain executables inside a certain runtime environment. See the runtime property of service metadata.

The plugin’s function takes an executable to run and an output collector. The output collector is a simple interface, to which the executable’s standard output should be forwarded. If required, the function can be a suspend function.

Use this plugin if you want to implement a special way to execute processing services. For example, you can implement a remote web service call, or you can use one of the existing runtimes and run a certain service in a special way (like in the example plugin below).

Type

runtime

Additional properties	Type
supportedRuntime (required)	string	The name of the `runtime` this plugin provides. Use this value in your service metadata.

Function interface

suspend fun myRuntime(executable: model.processchain.Executable,
  outputCollector: helper.OutputCollector, vertx: io.vertx.core.Vertx)

Example descriptor (Source)

- name: ignoreError
  type: runtime
  scriptFile: conf/plugins/ignoreError.kt
  supportedRuntime: ignoreError

Example plugin script (Source)

import helper.OutputCollector
import helper.Shell.ExecutionException
import io.vertx.core.Vertx
import model.processchain.Executable
import runtime.OtherRuntime

fun ignoreError(executable: Executable, outputCollector: OutputCollector, vertx: Vertx) {
  try {
    OtherRuntime().execute(executable, outputCollector)
  } catch (e: ExecutionException) {
    if (e.exitCode != 1) {
      throw e
    }
  }
}

8.6 Progress estimators

A progress estimator plugin is a function that analyses the log output of a running processing service to estimate its current progress. For example, the plugin can look for percentages or number of bytes processed. The returned value contributes to the execution progress of a process chain (see the estimatedProgress property of the process chain data model).

The function takes the executable that is currently being run and a list of recently collected output lines. It returns an estimated progress between 0.0 (0%) and 1.0 (100%) or null if the progress could not be determined. The function will be called for each output line collected and the newest line is always at the end of the given list. If required, the function can be a suspend function.

Type

progressEstimator

Additional properties	Type
supportedServiceIds (required)	array	An array of IDs of the services this estimator plugin supports

Function interface

suspend fun myProgressEstimator(executable: model.processchain.Executable,
  recentLines: List<String>, vertx: io.vertx.core.Vertx): Double?

Example descriptor

- name: extractArchiveProgressEstimator
  type: progressEstimator
  scriptFile: conf/plugins/extractArchiveProgressEstimator.kt
  supportedServiceIds:
    - extract-archive

Example plugin script

import model.processchain.Executable
import io.vertx.core.Vertx

suspend fun extractArchiveProgressEstimator(executable: Executable,
    recentLines: List<String>, vertx: Vertx): Double? {
  val lastLine = recentLines.last()
  val percentSign = lastLine.indexOf('%')
  if (percentSign > 0) {
    val percentStr = lastLine.substring(0, percentSign)
    val percent = percentStr.trim().toIntOrNull()
    if (percent != null) {
      return percent / 100.0
    }
  }
  return null
}

8.7 Parameter injection

For compatibility reasons, the plugin function signatures described above are not fixed. Whenever a plugin function is called, its arguments are injected based on their type. For example, if the function requires an instance of io.vertx.core.Vertx, such an object will be passed. This is independent of where this argument appears in the parameter list. In the function signatures described above, the Vert.x instance is always the last parameter, but actually, it could be at any position and the injection mechanism would still work.

This feature allows us as developers to add new parameters in the future to the function signatures without requiring all users to change their plugins. It also allows plugin developers to specify parameters in any order and to even leave out parameters if they are not needed. For example, a process chain adapter could also have the following signature:

fun myProcessChainAdapter(workflow: Workflow)

Note that a parameter can only be injected into a plugin of a certain type, if it is described in the function signature of this plugin type above. For example, the function signature of a runtime plugin does not specify a workflow, so a workflow cannot be injected. Trying to define a runtime plugin with such a parameter will result in an error.

About

Steep’s development is led by the competence center for Spatial Information Management of the Fraunhofer Institute for Computer Graphics Research IGD in Darmstadt, Germany. Fraunhofer IGD is the international leading research institution for applied visual computing. The competence center for Spatial Information Management offers expertise and innovative technologies that enable successful communication and efficient cooperation with the help of geographic information.

Steep was initially developed within the research project “IQmulus” (A High-volume Fusion and Analysis Platform for Geospatial Point Clouds, Coverages and Volumetric Data Sets) funded from the 7^th Framework Programme of the European Commission, call identifier FP7-ICT-2011-8, under the Grant agreement no. 318787 from 2012 to 2016. It was previously called the ‘IQmulus JobManager’ or just the ‘JobManager’.

Presentations

This presentation was given by Michel Krämer at the DATA conference 2020. He presented his paper entitled “Capability-based scheduling of scientific workflows in the cloud”. Michel talked about Steep’s software architecture and its scheduling algorithm that assigns process chains to virtual machines.

See slides ...

Publications

Steep and its predecessor JobManager have appeared in at least the following publications:

Krämer, M. (2021). Efficient Scheduling of Scientific Workflow Actions in the Cloud Based on Required Capabilities. In S. Hammoudi, C. Quix, & J. Bernardino (Eds.), Data Management Technologies and Applications. Communications in Computer and Information Science (Vol. 1446, pp. 32–55). Springer. https://doi.org/10.1007/978-3-030-83014-4_2
[ PDF ]

Krämer, M., Würz, H. M., & Altenhofen, C. (2021). Executing cyclic scientific workflows in the cloud. Journal of Cloud Computing, 10(25), 1–26. https://doi.org/10.1186/s13677-021-00229-7
[ PDF ]

Krämer, M. (2020). Capability-based Scheduling of Scientific Workflows in the Cloud. Proceedings of the 9th International Conference on Data Science, Technology, and Applications DATA, 43–54. https://doi.org/10.5220/0009805400430054
[ PDF ]

Krämer, M. (2018). A Microservice Architecture for the Processing of Large Geospatial Data in the Cloud (Doctoral dissertation). Technische Universität Darmstadt. https://doi.org/10.13140/RG.2.2.30034.66248
[ PDF ]

Böhm, J., Bredif, M., Gierlinger, T., Krämer, M., Lindenbergh, R., Liu, K., … Sirmacek, B. (2016). The IQmulus Urban Showcase: Automatic Tree Classification and Identification in Huge Mobile Mapping Point Clouds. ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, XLI-B3, 301–307. https://doi.org/10.5194/isprs-archives-XLI-B3-301-2016
[ PDF ]

Krämer, M., & Senner, I. (2015). A modular software architecture for processing of big geospatial data in the cloud. Computers & Graphics, 49, 69–81. https://doi.org/10.1016/j.cag.2015.02.005

Key features

Distributed

Cyclic workflow graphs

Capability-based scheduling

Automatic failover

Microservice integration

Runtime environments

Plugins

Optional databases

HTTP and web interfaces

Kubernetes

OpenStack

Scalability

Production-ready

Open-Source

Download and get started

Documentation

Table of contents

1 How does Steep work?

1.1 Workflow scheduling

1.2 Software architecture

1.3 Processing services

2 Example workflows

2.1 Running two services in parallel

Workflow:

Service metadata:

2.2 Chaining two services

Workflow:

2.3 Splitting and joining results

Workflow:

Service metadata:

2.4 Processing a dynamic number of results in parallel

Workflow:

Service metadata:

2.5 Feeding results back into the workflow (cycles/​loops)

Workflow:

Service metadata:

3 Data models

3.1 Workflows

Example:

3.2 Variables

Example:

3.3 Actions

3.3.1 Execute actions

Example:

3.3.2 For-each actions

Example:

3.3.3 Parameters

Example:

3.3.4 Output parameters

Example:

3.4 Process chains

Example:

3.4.1 Process chain status

3.5 Executables

Example:

3.5.1 Arguments

Example:

3.5.2 Argument variables

Example:

3.6 Submissions

Example:

3.6.1 Submission status

3.7 Service metadata

Example:

3.7.1 Runtime environments

3.7.2 Service parameters

Example cardinalities:

Data type:

Example:

3.7.3 Runtime arguments

Example:

3.8 Retry policies

Exponential backoff:

Example:

3.9 Timeout policies

Example:

3.10 Durations

Examples:

3.11 Agents

2.5 Feeding results back into the workflow (cycles/loops)

7.3 services/services.yaml

7.4 plugins/common.yaml