Actions provide a way to execute very quick tasks in a single Docker extension, using a single code base. The default component’s action (run) executes as a background, asynchronous job. It is queued, has plenty of execution time, and there are cases when you might not want to wait for it. Apart from the default run, there can be synchronous actions with limited execution time and you must wait for them. When we refer to actions, we mean synchronous actions. Using actions is fully optional.

Use Case

For example, in our database extractor, the main task (run action) is the data extraction itself. But we also want to be able to test the database credentials and list tables available in the database. These tasks would be very helpful in the UI. It is not possible to do these things directly in the browser. Setting up a separate application would bring an overhead of maintaining both the extractor’s Docker image and the new application.


For each registered Docker Extension or Custom Science App, you can specify other actions (apart from the default run). These actions will be executed using the same Docker image, but Docker Runner will wait for its execution and use the returned value as the API response. So, these additional actions are executed synchronously and have a very limited execution time (maximum 30 seconds). These actions also cannot access Storage.

Docker Actions overview

The configuration file contains the action property with the name of the currently executed action. Just grab the value and act accordingly. All actions must be explicitly specified when registering your component.

Running Actions

Actions are available through the API. They do not load the configuration from Storage, so you need to fully specify the whole configuration in the request body. If any of your parameters are encrypted, they will be decrypted before they are passed to your application.

Do not specify the action attribute in the request body, it is already in the URI. Use any of parameters and runtime inside the configData root element as you would when creating an asynchronous job. Using storage configuration in actions makes no sense, because actions cannot read or write to Storage. For instance:

    "configData": {
        "parameters": {
            "key": "val"

Important: use for calling this part of the API.

Return Values

As the application output is passed back through the API, all output from an action MUST be JSON (except for errors).

If your application outputs an invalid JSON on its STDOUT, an application error will be raised.

Handling User and Application errors

Actions use the same exit codes as the default run action.

If an user or application error is detected, STDERR/STDOUT is handled as the message string and is returned to the user. The message is wrapped into a standardized structure.

For example

print('user error message')

yields this message on the API (HTTP status code 400)

  "status": "error",
  "error": "User error",
  "code": 400,
  "message": "user error message",
  "exceptionId": "docker-7ed4c3b599776e8a2a84a7f185f5f7f2",
  "runId": 0


print('application error message')

yields this message on the API (HTTP status code 500)

  "status": "error",
  "error": "Application error",
  "code": 500,
  "message": "Contact and attach this exception id.",
  "exceptionId": "docker-2a51922e0753cf78297ad6d384200206",
  "runId": 0


Sync actions may not read from or write data to the Storage. Otherwise actions share the same limits as the default run action, only the execution time is limited to 30 seconds. This time does not include pulling the Docker image.