Dynamically process data with a Map state - AWS Step Functions

Dynamically process data with a Map state

This sample project demonstrates dynamic parallelism using a Map state. This sample project creates the following:

  • Two AWS Lambda functions

  • An Amazon Simple Queue Service (Amazon SQS) queue

  • An Amazon Simple Notification Service (Amazon SNS) topic

  • An Amazon DynamoDB table

  • An AWS Step Functions state machine

In this project, Step Functions uses an AWS 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:

Create the state machine and provision resources

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

  2. Choose Sample Projects, and then choose Dynamically process data with a Map state.

    The state machine Code and Visual Workflow are displayed.

            Map state workflow.
  3. Choose Next.

    The Deploy resources page is displayed, listing the resources that will be created. For this sample project, the resources include:

    • An Amazon SQS queue

    • An Amazon SNS topic

    • A DynamoDB table

    • Two Lambda functions

    • A Step Functions state machine

  4. Choose Deploy Resources.


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

Once the resources of the sample project are deployed, you need to add items to the Amazon SQS queue and subscribe to the Amazon SNS topic before you start an execution of the state machine.

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. Under Subscriptions, 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.

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. In the Queue Actions list, select Send a Message.

  4. On the Send a Message window, enter a message and choose Send Message.

  5. Choose Send Another Message.

    Continue entering messages until you have several in the Amazon SQS queue.

  6. Choose Close.

Start a new execution


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. Open the Step Functions console.

  2. On the State machines page, choose the MapStateStateMachine state machine that was created by the sample project and choose Start execution.

  3. On the New execution page, enter an execution name (optional), and then choose Start Execution.

  4. (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 state machine, execution, and activity names 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.

  5. (Optional) Go to the newly created state machine on the Step Functions Dashboard, and then choose New execution.

  6. When an execution is complete, you can select states on the Visual workflow and browse the Input and Output under Step details.

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 AWS Step Functions can control other AWS services, see Using AWS 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 AWS 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 AWS services, see IAM Policies for integrated services.