Transfer data records (Lambda, DynamoDB, Amazon SQS)

This sample project demonstrates how to iteratively read items from an Amazon DynamoDB table and send these items to an Amazon SQS queue using a Step Functions state machine. Deploying this sample project will create a Step Functions state machine, a DynamoDB table, an AWS Lambda function, and an Amazon SQS queue.

In this project, Step Functions uses the Lambda function to populate the DynamoDB table. The state machine also uses a for loop to read each of the entries, and then sends each entry to an Amazon SQS queue.

Step 1: Create the state machine and provision resources

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

2. Type Transfer data records in the search box, and then choose Transfer data records from the search results that are returned.

3. Choose Next to continue.

4. Step Functions lists the AWS services used in the sample project you selected. It also shows a workflow graph for the sample project. Deploy this project to your AWS 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:

   • A Lambda function for seeding the DynamoDB table

   • An Amazon SQS queue

   • A DynamoDB table

   • An AWS Step Functions state machine

   • Related AWS Identity and Access Management (IAM) roles

   The following image shows the workflow graph for the Transfer data records 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 AWS CloudFormation template to deploy the AWS resources listed in that template to your AWS 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 with DynamoDB and Amazon SQS by passing parameters directly to those resources.

Browse through this example state machine to see how Step Functions controls DynamoDB and Amazon SQS 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 a DynamoDB table and sending them to SQS",
  "StartAt": "Seed the DynamoDB Table",
  "TimeoutSeconds": 3600,
  "States": {
    "Seed the DynamoDB Table": {
      "Type": "Task",
      "Resource": "arn:aws:lambda:us-east-1:123456789012:function:sqsconnector-SeedingFunction-T3U43VYDU5OQ",
      "ResultPath": "$.List",
      "Next": "For Loop Condition"
    },
    "For Loop Condition": {
      "Type": "Choice",
      "Choices": [
        {
          "Not": {
            "Variable": "$.List[0]",
            "StringEquals": "DONE"
          },
          "Next": "Read Next Message from DynamoDB"
        }
      ],
      "Default": "Succeed"
    },
    "Read Next Message from DynamoDB": {
      "Type": "Task",
      "Resource": "arn:aws:states:::dynamodb:getItem",
      "Parameters": {
        "TableName": "sqsconnector-DDBTable-1CAFOJWP8QD6I",
        "Key": {
          "MessageId": {"S.$": "$.List[0]"}
        }
      },
      "ResultPath": "$.DynamoDB",
      "Next": "Send Message to SQS"
    },
    "Send Message to SQS": {
      "Type": "Task",
      "Resource": "arn:aws:states:::sqs:sendMessage",
      "Parameters": {
        "MessageBody.$": "$.DynamoDB.Item.Message.S",
        "QueueUrl": "https://sqs.us-east-1.amazonaws.com/123456789012/sqsconnector-SQSQueue-QVGQBW134PWK"
      },
      "ResultPath": "$.SQS",
      "Next": "Pop Element from List"
    },
    "Pop Element from List": {
      "Type": "Pass",
      "Parameters": {
        "List.$": "$.List[1:]"
      },
      "Next": "For Loop Condition"
    },
    "Succeed": {
      "Type": "Succeed"
    }
  }
}

For more information about passing parameters and managing results, see the following:

• Pass parameters to a service API

• ResultPath

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. It's a best practice to include only those permissions that are necessary in your IAM policies.

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Action": [
                "dynamodb:GetItem"
            ],
            "Resource": [
                "arn:aws:dynamodb:ap-northeast-1:123456789012:table/TransferDataRecords-DDBTable-3I41R5L5EAGT"
            ],
            "Effect": "Allow"
        },
        {
            "Action": [
                "sqs:SendMessage"
            ],
            "Resource": [
                "arn:aws:sqs:ap-northeast-1:123456789012:TransferDataRecords-SQSQueue-BKWXTS09LIW1"
            ],
            "Effect": "Allow"
        },
        {
            "Action": [
                "lambda:invokeFunction"
            ],
            "Resource": [
                "arn:aws:lambda:ap-northeast-1:123456789012:function:TransferDataRecords-SeedingFunction-VN4KY2TPAZSR"
            ],
            "Effect": "Allow"
        }
    ]
}

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