Services or capabilities described in Amazon Web Services documentation might vary by Region. To see the differences applicable to the China Regions, see Getting Started with Amazon Web Services in China (PDF).

Process High-Volume Messages from Amazon SQS (Express Workflows)

This sample project demonstrates how to use an Amazon Step Functions Express Workflow to process messages or data from a high-volume event source, such as Amazon Simple Queue Service (Amazon SQS). Because Express Workflows can be started at a very high rate, they are ideal for high-volume event processing or streaming data workloads.

Here are two commonly used methods to execute your state machine from an event source:

This sample project uses the second method to start an execution each time the Amazon SQS queue sends a message. You can use a similar configuration to trigger Express Workflows execution from other event sources, such as Amazon Simple Storage Service (Amazon S3), Amazon DynamoDB, and Amazon Kinesis.

For more information about Express Workflows and Step Functions service integrations, see the following:

Create the State Machine and Provision Resources

Trigger Execution

Example Lambda Function Code

The following is Lambda function code that shows how the initiating Lambda function starts a state machine execution using the Amazon SDK.

import boto3

def lambda_handler(event, context):
    message_body = event['Records'][0]['body']
    client = boto3.client('stepfunctions')
    response = client.start_execution(
        stateMachineArn='${ExpressStateMachineArn}',
        input=message_body
    )

Example State Machine Code

The Express Workflow in this sample project consists of a set of Lambda functions for text processing.

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 using Express workflows to run text processing for each message sent from an SQS queue.",
  "StartAt": "Decode base64 string",
  "States": {
    "Decode base64 string": {
      "Type": "Task",
      "Resource": "arn:<PARTITION>:states:::lambda:invoke",
      "OutputPath": "$.Payload",
      "Parameters": {
        "FunctionName": "<BASE64_DECODER_LAMBDA_FUNCTION_NAME>",
        "Payload.$": "$"
      },
      "Next": "Generate statistics"
    },
    "Generate statistics": {
      "Type": "Task",
      "Resource": "arn:<PARTITION>:states:::lambda:invoke",
      "OutputPath": "$.Payload",
      "Parameters": {
        "FunctionName": "<TEXT_STATS_GENERATING_LAMBDA_FUNCTION_NAME>",
        "Payload.$": "$"
      },
      "Next": "Remove special characters"
    },
    "Remove special characters": {
      "Type": "Task",
      "Resource": "arn:<PARTITION>:states:::lambda:invoke",
      "OutputPath": "$.Payload",
      "Parameters": {
        "FunctionName": "<STRING_CLEANING_LAMBDA_FUNCTION_NAME>",
        "Payload.$": "$"
      },
      "Next": "Tokenize and count"
    },
    "Tokenize and count": {
      "Type": "Task",
      "Resource": "arn:<PARTITION>:states:::lambda:invoke",
      "OutputPath": "$.Payload",
      "Parameters": {
        "FunctionName": "<TOKENIZING_AND_WORD_COUNTING_LAMBDA_FUNCTION_NAME>",
        "Payload.$": "$"
      },
      "End": true
    }
  }
}

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-cn:lambda:us-east-1:123456789012:function:example-Base64DecodeLambda-wJalrXUtnFEMI",
                "arn:aws-cn:lambda:us-east-1:123456789012:function:example-StringCleanerLambda-je7MtGbClwBF",
                "arn:aws-cn:lambda:us-east-1:123456789012:function:example-TokenizerCounterLambda-wJalrXUtnFEMI",
                "arn:aws-cn:lambda:us-east-1:123456789012:function:example-GenerateStatsLambda-je7MtGbClwBF"
            ],
            "Effect": "Allow"
        }
    ]
}

The folowing policy ensures that there are sufficient permissions for CloudWatch Logs.

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Action": [
                "logs:CreateLogDelivery",
                "logs:GetLogDelivery",
                "logs:UpdateLogDelivery",
                "logs:DeleteLogDelivery",
                "logs:ListLogDeliveries",
                "logs:PutResourcePolicy",
                "logs:DescribeResourcePolicies",
                "logs:DescribeLogGroups"
            ],
            "Resource": [
                "*"
            ],
            "Effect": "Allow"
        }
    ]
}

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