Dynamically process data with a Map state - Amazon Step Functions
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Dynamically process data with a Map state

This sample project demonstrates dynamic parallelism using a Map state.

In this project, Step Functions uses an Amazon Lambda function to pull messages off an Amazon SQS queue, and pass a JSON array of those message to a Map state. For each message in the queue, the state machine writes the message to DynamoDB, invokes the other Lambda function to remove the message from Amazon SQS, and then publishes the message to the Amazon SNS topic.

For more information on Map states and Step Functions service integrations, see the following:

Step 1: Create the state machine and provision resources

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

  2. Type Dynamically process data with a Map state in the search box, and then choose Dynamically process data with a Map state 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 Amazon SQS queue from which the Map state reads and removes messages iteratively.

    • A DynamoDB table to which the Map state writes messages iteratively.

    • An Amazon SNS topic to which Step Functions publishes the messages it reads from the Amazon SQS queue.

    • Two Amazon Lambda functions

    • An Amazon Step Functions state machine

    • Related Amazon Identity and Access Management (IAM) roles

    The following image shows the workflow graph for the Dynamically process data with a Map state sample project:

    Workflow graph of the Dynamically process data with a Map state 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.


      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.


      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.


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

After the resources of the sample project are deployed, you must add items to the Amazon SQS queue and subscribe to the Amazon SNS topic before you run the state machine.

Step 2: Subscribe to the Amazon SNS topic

  1. Open the Amazon SNS console.

  2. Choose Topics and choose the topic that was created by the Map state sample project.

    The name will be similar to MapSampleProj-SNSTopic-1CQO4HQ3IR1KN.

  3. Choose Create subscription.

    The Create subscription page is displayed, listing the Topic ARN for the topic.

  4. Under Protocol, choose Email.

  5. Under Endpoint, enter an email address to subscribe to the topic.

  6. Choose Create subscription.


    You must confirm the subscription in your email before it is active.

  7. Open the Subscription Confirmation email in the related account and open the Confirm subscription URL.

    The Subscription confirmed! page is displayed.

Step 3: Add messages to the Amazon SQS queue

  1. Open the Amazon SQS console.

  2. Choose the queue that was created by the Map state sample project.

    The name will be similar to MapSampleProj-SQSQueue-1UDIC9VZDORN7.

  3. Choose Send and receive messages.

  4. On the Send and receive messages page, enter a message and choose Send message.

  5. Entering another message and choose Send message. Continue entering more messages until you have several in the Amazon SQS queue.

Step 4: Run the state machine


Queues in Amazon SNS are eventually consistent. For best results, wait a few minutes between populating your queue and running an execution of your 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.


      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.


      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 with Amazon SQS, Amazon SNS, and Lambda by passing parameters directly to those resources.

Browse through this example state machine to see how Step Functions controls Lambda, DynamoDB, Amazon SNS by connecting to the Amazon Resource Name (ARN) in the Resource field, and by passing Parameters to the service API.

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 the Amazon States Language for reading messages from an SQS queue and iteratively processing each message.", "StartAt": "Read messages from SQS Queue", "States": { "Read messages from SQS Queue": { "Type": "Task", "Resource": "arn:aws:states:::lambda:invoke", "OutputPath": "$.Payload", "Parameters": { "FunctionName": "MapSampleProj-ReadFromSQSQueueLambda-1MY3M63RMJVA9" }, "Next": "Are there messages to process?" }, "Are there messages to process?": { "Type": "Choice", "Choices": [ { "Variable": "$", "StringEquals": "No messages", "Next": "Finish" } ], "Default": "Process messages" }, "Process messages": { "Type": "Map", "Next": "Finish", "ItemsPath": "$", "Parameters": { "MessageNumber.$": "$$.Map.Item.Index", "MessageDetails.$": "$$.Map.Item.Value" }, "Iterator": { "StartAt": "Write message to DynamoDB", "States": { "Write message to DynamoDB": { "Type": "Task", "Resource": "arn:aws:states:::dynamodb:putItem", "ResultPath": null, "Parameters": { "TableName": "MapSampleProj-DDBTable-YJDJ1MKIN6C5", "ReturnConsumedCapacity": "TOTAL", "Item": { "MessageId": { "S.$": "$.MessageDetails.MessageId" }, "Body": { "S.$": "$.MessageDetails.Body" } } }, "Next": "Remove message from SQS queue" }, "Remove message from SQS queue": { "Type": "Task", "Resource": "arn:aws:states:::lambda:invoke", "InputPath": "$.MessageDetails", "ResultPath": null, "Parameters": { "FunctionName": "MapSampleProj-DeleteFromSQSQueueLambda-198J2839ZO5K2", "Payload": { "ReceiptHandle.$": "$.ReceiptHandle" } }, "Next": "Publish message to SNS topic" }, "Publish message to SNS topic": { "Type": "Task", "Resource": "arn:aws:states:::sns:publish", "InputPath": "$.MessageDetails", "Parameters": { "Subject": "Message from Step Functions!", "Message.$": "$.Body", "TopicArn": "arn:aws:sns:us-east-1:012345678910:MapSampleProj-SNSTopic-1CQO4HQ3IR1KN" }, "End": true } } } }, "Finish": { "Type": "Succeed" } } }

IAM example

This example Amazon Identity and Access Management (IAM) policy generated by the sample project includes the least privilege necessary to execute the state machine and related resources. We recommend that you include only those permissions that are necessary in your IAM policies.

{ "Version": "2012-10-17", "Statement": [ { "Action": [ "lambda:InvokeFunction" ], "Resource": [ "arn:aws:lambda:us-east-1:012345678901:function:MapSampleProj-ReadFromSQSQueueLambda-1MY3M63RMJVA9", "arn:aws:lambda:us-east-1:012345678901:function:MapSampleProj-DeleteFromSQSQueueLambda-198J2839ZO5K2" ], "Effect": "Allow" }, { "Action": [ "dynamodb:PutItem" ], "Resource": [ "arn:aws:dynamodb:us-east-1:012345678901:table/MapSampleProj-DDBTable-YJDJ1MKIN6C5" ], "Effect": "Allow" }, { "Action": [ "sns:Publish" ], "Resource": [ "arn:aws:sns:us-east-1:012345678901:MapSampleProj-SNSTopic-1CQO4HQ3IR1KN" ], "Effect": "Allow" } ] }

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