Start a Workflow within a Workflow (Step Functions, Lambda) - Amazon Step Functions
Step 1: Create the state machine and provision resourcesStep 2: Run the state machineExample State Machine Code
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Start a Workflow within a Workflow (Step Functions, Lambda)

This sample project demonstrates how to use an Amazon Step Functions state machine to start other state machine executions. For information about starting state machine executions from another state machine, see Start Workflow Executions from a Task State.

Step 1: Create the state machine and provision resources

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

  2. Type Start a workflow within a workflow in the search box, and then choose Start a workflow within a workflow from the search results that are returned.

  3. Choose Next to continue.

  4. Step Functions lists the Amazon Web Services used in the sample project you selected. It also shows a workflow graph for the sample project. Deploy this project to your Amazon Web Services account or use it as a starting point for building your own projects. Based on how you want to proceed, choose Run a demo or Build on it.

    This sample project deploys the following resources:

    • An additional state machine. The execution of this state machine is started by the state machine that you run.

    • A callback Lambda function. This function is used in the additional state machine to implement the callback mechanism.

    • An Amazon Step Functions state machine

    • Related Amazon Identity and Access Management (IAM) roles

    The following image shows the workflow graph for the Start a workflow within a workflow sample project:

    Workflow graph of the Start a workflow within a workflow sample project.

  5. Choose Use template to continue with your selection.

  6. Do one of the following:

    • If you selected Build on it, Step Functions creates the workflow prototype for the sample project you selected. Step Functions doesn't deploy the resources listed in the workflow definition.

      In Workflow Studio's Design mode, drag and drop states from the States browser to continue building your workflow protoype. Or switch to the Code mode that provides an integrated code editor similar to VS Code for updating the Amazon States Language (ASL) definition of your state machine within the Step Functions console. For more information about using Workflow Studio to build your state machines, see Using Workflow Studio.

      Important

      Remember to update the placeholder Amazon Resource Name (ARN) for the resources used in the sample project before you run your workflow.

    • If you selected Run a demo, Step Functions creates a read-only sample project which uses an Amazon CloudFormation template to deploy the Amazon resources listed in that template to your Amazon Web Services account.

      Tip

      To view the state machine definition of the sample project, choose Code.

      When you're ready, choose Deploy and run to deploy the sample project and create the resources.

      It can take up to 10 minutes for these resources and related IAM permissions to be created. While your resources are being deployed, you can open the CloudFormation Stack ID link to see which resources are being provisioned.

      After all the resources in the sample project are created, you can see the new sample project listed on the State machines page.

      Important

      Standard charges may apply for each service used in the CloudFormation template.

Step 2: Run the state machine

  1. On the State machines page, choose your sample project.

  2. On the sample project page, choose Start execution.

  3. 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.

      If you chose to Run a demo, you need not provide any execution input.

      Note

      If the demo project you deployed contains prepopulated execution input data, use that input to run the state machine.

    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.

Example State Machine Code

The state machine in this sample project integrates another state machine and Amazon Lambda by passing parameters directly to those resources.

Browse through this example state machine to see how Step Functions calls the StartExecution API action for the other state machine. It launches two instances of the other state machine in parallel: one using the Run a Job (.sync) pattern and one using the Wait for a Callback with the Task Token pattern.

For more information about how Amazon Step Functions can control other Amazon services, see Using Amazon Step Functions with other services.

{
  "Comment": "An example of combining workflows using a Step Functions StartExecution task state with various integration patterns.",
  "StartAt": "Start new workflow and continue",
  "States": {
    "Start new workflow and continue": {
      "Comment": "Start an execution of another Step Functions state machine and continue",
      "Type": "Task",
      "Resource": "arn:aws:states:::states:startExecution",
      "Parameters": {
        "StateMachineArn": "arn:aws:states:us-east-1:123456789012:stateMachine:NestingPatternAnotherStateMachine-HZ9gtgspmdun",
        "Input": {
          "NeedCallback": false,
          "AWS_STEP_FUNCTIONS_STARTED_BY_EXECUTION_ID.$": "$$.Execution.Id"
        }
      },
      "Next": "Start in parallel"
    },
    "Start in parallel": {
      "Comment": "Start two executions of the same state machine in parallel",
      "Type": "Parallel",
      "End": true,
      "Branches": [
        {
          "StartAt": "Start new workflow and wait for completion",
          "States": {
            "Start new workflow and wait for completion": {
              "Comment": "Start an execution of the same 'NestingPatternAnotherStateMachine' and wait for its completion",
              "Type": "Task",
              "Resource": "arn:aws:states:::states:startExecution.sync",
              "Parameters": {
                "StateMachineArn": "arn:aws:states:us-east-1:123456789012:stateMachine:NestingPatternAnotherStateMachine-HZ9gtgspmdun",
                "Input": {
                  "NeedCallback": false,
                  "AWS_STEP_FUNCTIONS_STARTED_BY_EXECUTION_ID.$": "$$.Execution.Id"
                }
              },
              "OutputPath": "$.Output",
              "End": true
            }
          }
        },
        {
          "StartAt": "Start new workflow and wait for callback",
          "States": {
            "Start new workflow and wait for callback": {
              "Comment": "Start an execution and wait for it to call back with a task token",
              "Type": "Task",
              "Resource": "arn:aws:states:::states:startExecution.waitForTaskToken",
              "Parameters": {
                "StateMachineArn": "arn:aws:states:us-east-1:123456789012:stateMachine:NestingPatternAnotherStateMachine-HZ9gtgspmdun",
                "Input": {
                  "NeedCallback": true,
                  "AWS_STEP_FUNCTIONS_STARTED_BY_EXECUTION_ID.$": "$$.Execution.Id",
                  "TaskToken.$": "$$.Task.Token"
                }
              },
              "End": true
            }
          }
        }
      ]
    }
  }
}

For information about how to configure IAM when using Step Functions with other Amazon services, see IAM Policies for integrated services.