Using a Step Functions API action to continue a new execution (recommended) - Amazon Step Functions
Step 1: Create a long-running state machineStep 2: Create a state machine to call the Step Functions API actionStep 3: Update the IAM policyStep 4: Run the state machine
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Using a Step Functions API action to continue a new execution (recommended)

Step Functions can start workflow executions by calling its own API as an integrated service. We recommend that you use this approach to avoid exceeding service quotas for long-running executions.

Step 1: Create a long-running state machine

Create a long-running state machine that you want to start from the Task state of a different state machine. For this tutorial, use the state machine that uses a Lambda function.

Note

Make sure to copy the name and Amazon Resource Name of this state machine in a text file for later use.

Step 2: Create a state machine to call the Step Functions API action

To start workflow executions from a Task state

  1. Open the Step Functions console and choose Create state machine.

  2. In the Choose a template dialog box, select Blank.

  3. Choose Select. This opens Workflow Studio in Design mode.

  4. From the Actions tab, drag the StartExecution API action and drop it on the empty state labelled Drag first state here.

  5. Choose the StartExecution state and do the following in the Configuration tab in Design mode:

    1. Rename the state to Start nested execution.

    2. For Integration type, choose Amazon SDK - new from the dropdown list.

    3. In API Parameters, do the following:

      1. For StateMachineArn, replace the sample Amazon Resource Name with the ARN of your state machine. For example, enter the ARN of the state machine that uses Lambda.

      2. For Input node, replace the existing placeholder text with the following value:

        "Comment": "Starting workflow execution using a Step Functions API action"

      3. Make sure your inputs in API Parameters look similar to the following:

        {
  "StateMachineArn": "arn:aws-cn:states:us-west-2:123456789012:stateMachine:LambdaStateMachine",
  "Input": {
    "Comment": "Starting workflow execution using a Step Functions API action",
    "AWS_STEP_FUNCTIONS_STARTED_BY_EXECUTION_ID.$": "$$.Execution.Id"
  }

  6. (Optional) Choose Definition on the Inspector panel to view the automatically-generated Amazon States Language (ASL) definition of your workflow.

    Tip

    You can also view the ASL definition in the Code editor of Workflow Studio. In the code editor, you can also edit the ASL definition of your workflow.

  7. Specify a name for your state machine. To do this, choose the edit icon next to the default state machine name of MyStateMachine. Then, in State machine configuration, specify a name in the State machine name box.

    For this tutorial, enter the name ParentStateMachine.

  8. (Optional) In State machine configuration, specify other workflow settings, such as state machine type and its execution role.

    For this tutorial, keep all the default selections in State machine settings.

    If you've previously created an IAM role with the correct permissions for your state machine and want to use it, in Permissions, select Choose an existing role, and then select a role from the list. Or select Enter a role ARN and then provide an ARN for that IAM role.

  9. In the Confirm role creation dialog box, choose Confirm to continue.

    You can also choose View role settings to go back to State machine configuration.

    Note

    If you delete the IAM role that Step Functions creates, Step Functions can't recreate it later. Similarly, if you modify the role (for example, by removing Step Functions from the principals in the IAM policy), Step Functions can't restore its original settings later.

Step 3: Update the IAM policy

To make sure your state machine has permissions to start the execution of the state machine that uses a Lambda function, you need to attach an inline policy to your state machine's IAM role. For more information, see Embedding Inline Policies in the IAM User Guide.

  1. On the ParentStateMachine page, choose the IAM role ARN to navigate to the IAM Roles page for your state machine.

  2. Assign an appropriate permission to the IAM role of the ParentStateMachine for it to be able to start execution of another state machine. To assign the permission, do the following:

    1. On the IAM Roles page, choose Add permissions, and then choose Create inline policy.

    2. On the Create policy page, choose the JSON tab.

    3. Replace the existing text with the following policy.

      {
  "Version": "2012-10-17",
  "Statement": [
      {
          "Effect": "Allow",
          "Action": [
              "states:StartExecution"
          ],
          "Resource": [
              "arn:aws-cn:states:us-west-2:123456789012:stateMachine:LambdaStateMachine"
          ]
      }
  ]
}

    4. Choose Review policy.

    5. Specify a name for the policy, and then choose Create policy.

Step 4: Run the state machine

State machine executions are instances where you run your workflow to perform tasks.

  1. On the ParentStateMachine page, choose Start execution.

    The Start execution dialog box is displayed.

  2. In the Start execution dialog box, do the following:

    1. (Optional) To identify your execution, you can specify a name for it in the Name box. By default, Step Functions generates a unique execution name automatically.

      Note

      Step Functions allows you to create names for state machines, executions, and activities, and labels that contain non-ASCII characters. These non-ASCII names don't work with Amazon CloudWatch. To ensure that you can track CloudWatch metrics, choose a name that uses only ASCII characters.

    2. (Optional) In the Input box, enter input values in JSON format to run your workflow.

    3. Choose Start execution.

    4. The Step Functions console directs you to a page that's titled with your execution ID. This page is known as the Execution Details page. On this page, you can review the execution results as the execution progresses or after it's complete.

      To review the execution results, choose individual states on the Graph view, and then choose the individual tabs on the Step details pane to view each state's details including input, output, and definition respectively. For details about the execution information you can view on the Execution Details page, see Execution Details page – Interface overview.

  3. Open the LambdaStateMachine page and notice a new execution triggered by the ParentStateMachine.