Using Inline Map state to repeat an action - AWS Step Functions

Using Inline Map state to repeat an action

This tutorial helps you get started with using the Map state in Inline mode. You use the Inline Map state in your workflows to repeatedly perform an action. For more information about Inline mode, see Map state in Inline mode.

In this tutorial, you use the Inline Map state to repeatedly generate version 4 universally unique identifiers (v4 UUID). You start by creating a workflow that contains two Pass states and an Inline Map state in the Workflow Studio. Then, you configure the input and output, including the input JSON array for the Map state. The Map state returns an output array that contains the v4 UUIDs generated for each item in the input array.

Step 1: Create the workflow prototype

In this step, you create the prototype for your workflow using Workflow Studio. Workflow Studio is a visual workflow designer available in the Step Functions console. You’ll choose the required states from the Flow tab and use the drag and drop feature of Workflow Studio to create the workflow prototype.

  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 Flow tab, drag a Pass state and drop it to the empty state labelled Drag first state here.

  5. Drag a Map state and drop it below the Pass state. Rename the Map state to Map demo.

  6. Drag a second Pass state and drop it inside of the Map demo state.

  7. Rename the second Pass state to Generate UUID.

Step 2: Configure input and output

In this step, you configure input and output for all the states in your workflow prototype. First, you inject some fixed data into the workflow using the first Pass state. This Pass state passes on this data as input to the Map demo state. Within this input, you specify the node that contains the input array the Map demo state should iterate over. Then you define the step that the Map demo state should repeat to generate the v4 UUIDs. Finally, you configure the output to return for each repetition.

  1. Choose the first Pass state in your workflow prototype. In the Output tab, enter the following under Result:

    { "foo": "bar", "colors": [ "red", "green", "blue", "yellow", "white" ] }
  2. Choose the Map demo state and in the Configuration tab, do the following:

    1. Choose Provide a path to items array.

    2. Specify the following reference path to select the node that contains the input array:

      $.colors
  3. Choose the Generate UUID state and in the Input tab, do the following:

    1. Choose Transform input with Parameters.

    2. Enter the following JSON input to generate the v4 UUIDs for each of the input array items. You use the States.UUID intrinsic function to generate the UUIDs.

      { "uuid.$": "States.UUID()" }
  4. For the Generate UUID state, choose the Output tab and do the following:

    1. Choose Filter output with OutputPath.

    2. Enter the following reference path to select the JSON node that contains the output array items:

      $.uuid

Step 3: Review the auto-generated Amazon States Language definition and save the workflow

As you drag and drop states from the Flow panel onto the canvas, Workflow Studio automatically composes the Amazon States Language (ASL) definition of your workflow in real-time. You can edit this definition as required.

  1. (Optional) Choose Definition on the Inspector panel to view the automatically-generated Amazon States Language 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.

    The following example shows the automatically generated Amazon States Language definition for your workflow.

    { "Comment": "Using Map state in Inline mode", "StartAt": "Pass", "States": { "Pass": { "Type": "Pass", "Next": "Map demo", "Result": { "foo": "bar", "colors": [ "red", "green", "blue", "yellow", "white" ] } }, "Map demo": { "Type": "Map", "ItemsPath": "$.colors", "ItemProcessor": { "ProcessorConfig": { "Mode": "INLINE" }, "StartAt": "Generate UUID", "States": { "Generate UUID": { "Type": "Pass", "End": true, "Parameters": { "uuid.$": "States.UUID()" }, "OutputPath": "$.uuid" } } }, "End": true } } }
  2. 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 InlineMapDemo.

  3. (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 configuration.

  4. 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 4: Run the state machine

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

  1. On the InlineMapDemo page, choose Start execution.

  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 automatically generates a unique execution name.

      Note

      Step Functions allows you to create names for state machines, executions, activities, rate controls, 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.

    To view the execution input and output side-by-side, choose Execution input and output. Under Output, view the output array returned by the Map state. The following is an example of the output array:

    [ "a85cbc7b-4e65-4ac2-97af-80ed504adc1d", "b05bca11-d481-414e-aa9a-88285ec6590d", "f42d59f7-bd32-480f-b270-caddb518ce2a", "15f18616-517d-4b69-b7c3-bf22222d2efd", "690bcfee-6d58-408c-a6b4-1995ccafdbd2" ]