SMILA/Documentation/WorkerAndWorkflows

Available since SMILA 0.9!

Workers and Workflows

This page is work in progress.

Workers

Worker Definition

The worker definition is provided with software. It defines default workers provided and must not be changed by the user.

Worker definitions cannot be added at runtime. They describe worker behaviour as needed by job manager to generate appropriate tasks and data objects.

Required input and output data is described in terms of bucket types as defined before. Additional string parameters may be needed and must be defined when used in workflow. Values for these parameters must be added as properties to the tasks created for this worker. (I.e. the names of all input and output slots have to be explicitly linked to names of existing buckets by the workflow referencing the workers as actions, see below. The workflow doesn't not need to define output slots which are marked as optional.)

As an advanced feature, output slots can be arranged into groups. The purpose of this is to describe which slots must or must not be used together: In a single workflow action it is not possible to use slot from different groups, but only slots of a single group and slots that are not marked with a group (they belong to each group implicitly). When using groups, the rules concerning optional and mandatory slots are as follows:

• A non-optional slot without a group must be always be connected to a bucket.
• An optional slot without a group is allowed in combination with any group slot.
• If a group is used, all non-optional slots of the same group must be connected to a bucket, too.
• If each group contains at least one non-optional slot, at least one group must be connected. It's not possible to use only the groupless slots then.

The worker properties in detail:

• name is mandatory.
• modes is optional and describes the mode of the worker
  • bulkSource: Can start a workflow, does not need input data. A task for this worker is created on demand when the worker requests it (in-progress tasks only)
  • autoCommit: When the worker dies while working on a task (sends no keep-alive anymore) the started bulks are committed by the job manager and follow-up actions are triggered, the task is not rolled back.
• parameters is optional and describes the parameters needed to configure the worker
• taskGenerator is optional and configures a piece of code (OSGi service) that is used to create the actual tasks after changes in the input buckets. Can be used to create multiple tasks for a single change event, or to filter events: If the generator does not actually create a task for the event, the action is cancelled.

List workers

All workers

Use a GET request to list all worker definitions.

Supported operations:

• GET: Returns a list of all worker definitions.

Usage:

• URL: http://<hostname>:8080/smila/jobmanager/workers/
• Allowed methods:
  • GET
• Response status codes:
  • 200 OK: Upon successful execution.

Specific worker

Use a GET request to list the definition of a specific worker.

Supported operations:

• GET: Returns the definition of the given worker.

Usage:

• URL: http://<hostname>:8080/smila/jobmanager/workers/<worker-name>/
• Allowed methods:
  • GET
• Response status codes:
  • 200 OK: Upon successful execution.

Workflows

Workflow Definition

Describes the work to be done by associating buckets to workers. All input and output slots of workers must be associated to buckets. The types of buckets must match the required bucket types described in the worker definition.

A workflow run starts with the start-action. The order of the other actions is determined by their inputs and outputs.

Description of a workflow:

• name
  • MANDATORY
  • The name of a workflow
• parameters (MAP)
  • The parameters defined within this workflow as a map
• startAction (MAP)
  • MANDATORY
  • the starting action of this workflow
  • there can be only one starting action
• actions (LIST of MAPs)
  • the non-starting-actions of this workflow which

Description of an action

• worker
  • the name of an existing worker definition
• parameters
  • the parameters the workflow defines for this worker (not for the buckets the worker uses!)
• input (MAP)
  • The mapping of the worker's named input slots (KEY) to an existing bucket definition (VALUE)
  • all of the worker's named input slots have to be resolved against an existing bucket of the same type.
• output (MAP)
  • The mapping of the worker's named output slots (KEY) to an existing bucket definition (VALUE)
  • all of the worker's named output slots have to be resolved against an existing bucket of the same type.

Parameters

We have two kinds of parameters in the workflow definition:

• Global workflow parameters: Parameters that are set globally and apply to every action in the workflow.
• Local worker parameters: Parameters that are set locally and are applied only to the action in which they were defined.

Please note that the local parameters do not affect the buckets that the respective worker is using. As a consequence, parameters declared in a data object type can only be initialized using global workflow parameters or job parameters alternatively.

Sample:

    {
      "name": "myWorkflow",
      "parameters": 
        {
            "myGlobalParam": "..."
        }
      "startAction":
        {
          "parameters": 
            {
               "myLocalParam": "..."
            }
          "worker": "myWorker",
       ...

Data object types and workers define parameter variables: ${...}

• Needed data object type variables that are not set in a bucket parameter must be either set as workflow or job parameter.
• Needed worker variables must be either set as workflow or job parameter.

List, create, and modify workflows

All workflows

Use a GET request to list the definitions of all workflows. Use POST for adding or updating a workflow definition.

Supported operations:

• GET: Returns a list of all workflow definitions. If there are no workflows defined, you will get an empty list.
• POST: Create a new workflow definition or update an existing one. If the workflow already exists, it will be updated after successful validation. However, the changes will not apply until the next job run, i.e. the current job run is not influenced by the changes. Only workers for which worker definitions exist can be added to the workflow definition as actions. When adding a worker, all parameters defined in the worker's definition have to be satisfied. If not in the global or local sections of the workflow definition itself, then later in the job definition. Also, all input and output slots have to be connected to existing buckets if they are persistent ones or at least a bucket name must be provided in case of transient ones. Expceptions to this rule are optional slots or those of other slot groups which need not and must not (in the latter case) be connected to buckets. An error will be thrown:
  • If a required slot is not connected to a bucket.
  • If a referenced bucket, defined as persistent one, does not exist.

Usage:

• URL: http://<hostname>:8080/smila/jobmanager/workflows.
• Allowed methods:
  • GET
  • POST
• Response status codes:
  • 200 OK: Upon successful execution (GET).
  • 201 CREATED: Upon successful execution (POST).
  • 400 Bad Request: name, startAction are mandatory fields. If they are not set, an HTTP 400 Bad Request including an error message in the response body will be returned.

Specific workflow

Use a GET request to retrieve the defintion of a specific workflow. Use DELETE to delete a specific workflow.

Supported operations:

• GET: Returns the definition of the given workflow.
• DELETE: Deletes the given workflow.

Usage:

• URL: http://<hostname>:8080/smila/jobmanager/workflows/
• Allowed methods:
  • GET
  • DELETE
• Response status codes:
  • 200 OK: Upon successful execution (GET, DELETE). If the workflow to be deleted does not exist, you will get 200 anyway (DELETE).
  • 404 Not Found: If the workflow does not exist (GET).
  • 400 Bad Request: If the workflow to be deleted is stil referenced by a job definition (DELETE).