Task steps

Attributes

A task step invokes a Function Compute function.

A task step contains the following attributes:

• type: the step type. The value task indicates that the step is a task step.
• name: the name of the step.
• resourceArn: the resource identifier. Supported types: functions, MNS queues, and Serverless workflow flow. Example: acs:fc:cn-shanghai:18807708****3420:services/fnf_test/functions/hello. Service Integration.
• Optional:pattern: execution mode for the integration service. Default value: requestResponse. Valid values:
  • requestResponse: Waits for the task to complete before continuing.
  • sync: Submits the task asynchronously and waits for the execution result before continuing.
  • waitForCallback: Submits the task asynchronously and suspends the step until a callback or timeout is received.
• Optional:timeoutSeconds: task timeout in seconds. The step times out if execution exceeds this duration.
• Optional:end: whether to continue to subsequent steps after this step completes.
• Optional:inputMappings: input mappings. The step input is passed as the function invocation event. For more information, see InvokeFunction.
• Optional:outputMappings: output mappings. $local is the function invocation result and must be in JSON format.
  Note If no output mappings are specified, $local is the default step output.
• Optional:errorMappings: error mappings. Valid only when an error occurs during step execution and the catch parameter is specified. You can use the $local.cause and $local.error values to map error information to the output for the next step.
  Note The $local.error and $local.code values are reserved for the system. The source field in errorMappings must be set to these two values. Examples. The errorMappings parameter is optional. If omitted, error information is unavailable in the next step.
• retry: retry policies. Each policy has the following attributes:
  • errors: one or more errors from the Error definitions table.
  • intervalSeconds: initial retry interval in seconds. Maximum: 86,400. Default: 1.
  • maxIntervalSeconds: maximum retry interval. Maximum and default: 86,400 seconds.
  • maxAttempts: maximum retry count. Default: 3.
  • multiplier: multiplier applied to each successive retry interval. Default: 2.
• catch: catch policies. Each policy has the following attributes:
  • errors: one or more errors from the error definitions table.
  • goto: destination step name.
    Note The destination step must be a step parallel to the current task step.

Examples

• Simple task steps

  The following sample flow contains a task step.

  • If the input is {"name": "function flow"}, the output is {"hello": "function flow"}.
  • If no input is provided or the input lacks the name key, the task step fails and the flow fails.
  • Define the flow.

    version: v1
    type: flow
    steps:
      - type: task
        name: hello
        resourceArn: acs:fc:{region}:{accountID}:services/fnf_test/functions/hello           

    Parameters of resourceArn:

    • {region}: Replace with the actual region, such as cn-shanghai.
    • {accountID}: Replace with your account ID. Find your account ID by clicking the profile picture on the Flows page of the Serverless Workflow console.
  • Define the function.

    import json
    
    class MyError(Exception):
      pass
    
    def handle(event, context):
      evt = json.loads(event)
      if "name" in evt:
        return {
          "hello": evt["name"]
        }
      else:
        raise MyError("My unhandled exception")          

• Retry

  This example retries a task on MyError. If no input is provided or the input lacks the name key, Serverless workflow retries the task according to the retry policy.

  • Waits 3 seconds after the first error, then retries.
  • Waits 6 seconds (intervalSeconds x multiplier) after the second error, then retries.
  • Waits 12 seconds (intervalSeconds x multiplier x multiplier) after the third error, then retries.
  • If the error persists after three retries, maxAttempts is exceeded, the task step fails, and the flow fails.

  version: v1
  type: flow
  steps:
    - type: task
      name: hello
      resourceArn: acs:fc:{region}:{accountID}:services/fnf_test/functions/hello
      retry:
        - errors:
          - MyError
          intervalSeconds: 3
          maxAttempts: 3
          multiplier: 2            

• Catch errors

  This example catches MyError and jumps to the final step. Because the error is caught, the flow succeeds.

  version: v1
  type: flow
  steps:
    - type: task
      name: hello
      resourceArn: acs:fc:{region}:{accountID}:services/fnf_test/functions/hello
      catch:
        - errors:
          - MyError
          goto: final
    - type: pass
      name: pass1
    - type: pass
      name: final           

• Catch errors with error mappings specified

  This example catches MyError and jumps to the final step. With error mappings specified, the final step can access error details. You can also use errorMappings to map step inputs and constants to outputs.

  version: v1
  type: flow
  steps:
    - type: task
      name: hello
      resourceArn: acs:fc:{region}:{accountID}:services/fnf_test/functions/hello
      errorMappings:
        - target: errMsg
          source: $local.cause # This value is reserved for the system and can be used directly when an error occurs in this step.
        - target: errCode
          source: $local.error # This value is reserved for the system and can be used directly when an error occurs in this step.
      catch:
        - errors:
          - MyError
          goto: final
    - type: pass
      name: pass1
    - type: pass
      name: final  

  The event of the final step contains the following EventDetail:

  "EventDetail": "{\"input\":{},\"local\":{\"errorCode\":\"MyError\",\"errorMsg\":\"some message\"}}",