Lambda orchestration example

This sample project demonstrates how to integrate Amazon Lambda functions in Step Functions state machines. This sample project creates the following resources:

In this project, Step Functions uses Lambda functions to check a stock price and determine a buy or sell trading recommendation. The user is then provided this recommendation and can choose whether to buy or sell the stock. The result of the trade is returned using an SNS topic.

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

Create the State Machine and Provision Resources

Start a New Execution

After all the resources are provisioned and deployed, the Start execution dialog box is displayed.

About the state machine and its execution

The state machine in this sample project integrates with Amazon Lambda by passing parameters directly to those resources, uses an Amazon SQS queue to manage the request for human approval, and uses an Amazon SNS topic to return the results of the query.

A Step Functions execution receives a JSON text as input and passes that input to the first state in the workflow. Individual states receive JSON data as input and usually pass JSON data as output to the next state. In this sample project, the output of each step is passed as input to the next step in the workflow. For example, the Generate Buy/Sell recommendation step receives the output of the Check Stock Price step as input. Further, the output of the Generate Buy/Sell recommendation step is passed as input to the next step, Request Human Approval, which mimics a human approval step.

To implement a human approval step, you typically pause the workflow execution until a task token is returned. In this sample project, a message is passed to an Amazon SQS queue, which is used as a trigger to the Lambda function defined to handle callback functionality. The message contains a task token and the output returned by the preceding step. The Lambda function is invoked with the payload of the message. The workflow execution is paused until it receives the task token back with a SendTaskSuccess API call. For more information about task tokens, see Wait for a Callback with the Task Token.

The following code for the StepFunctionsSample-HelloLambda-ApproveSqsLambda function shows how it is defined to automatically approve any tasks submitted by the Amazon SQS queue through the Step Functions state machine.

exports.lambdaHandler = (event, context, callback) => {
  const stepfunctions = new aws.StepFunctions();

  // For every record in sqs queue
  for (const record of event.Records) {
      const messageBody = JSON.parse(record.body);
      const taskToken = messageBody.TaskToken;

      const params = {
          output: "\"approved\"",
          taskToken: taskToken
      };

      console.log(`Calling Step Functions to complete callback task with params ${JSON.stringify(params)}`);

      // Approve
      stepfunctions.sendTaskSuccess(params, (err, data) => {
          if (err) {
              console.error(err.message);
              callback(err.message);
              return;
          }
          console.log(data);
          callback(null);
      });
  }
};

Browse through this example state machine to see how Step Functions controls Lambda and Amazon SQS.

For more information about how Amazon Step Functions can control other Amazon services, see Using Amazon Step Functions with other services.

{
    "StartAt": "Check Stock Price",
    "States": {
        "Check Stock Price": {
            "Type": "Task",
            "Resource": "arn:aws:lambda:us-west-1:111122223333:function:StepFunctionsSample-HelloLam-CheckStockPriceLambda-444455556666",
            "Next": "Generate Buy/Sell recommendation"
        },
        "Generate Buy/Sell recommendation": {
            "Type": "Task",
            "Resource": "arn:aws:lambda:us-west-1:111122223333:function:StepFunctionsSample-Hello-GenerateBuySellRecommend-123456789012",
            "ResultPath": "$.recommended_type",
            "Next": "Request Human Approval"
        },
        "Request Human Approval": {
            "Type": "Task",
            "Resource": "arn:aws:states:::sqs:sendMessage.waitForTaskToken",
            "Parameters": {
                "QueueUrl": "https://sqs.us-west-1.amazonaws.com/111122223333/StepFunctionsSample-HelloLambda4444-5555-6666-RequestHumanApprovalSqs-777788889999",
                "MessageBody": {
                    "Input.$": "$",
                    "TaskToken.$": "$$.Task.Token"
                }
            },
            "ResultPath": null,
            "Next": "Buy or Sell?"
        },
        "Buy or Sell?": {
            "Type": "Choice",
            "Choices": [
                {
                    "Variable": "$.recommended_type",
                    "StringEquals": "buy",
                    "Next": "Buy Stock"
                },
                {
                    "Variable": "$.recommended_type",
                    "StringEquals": "sell",
                    "Next": "Sell Stock"
                }
            ]
        },
        "Buy Stock": {
            "Type": "Task",
            "Resource": "arn:aws:lambda:us-west-1:111122223333:function:StepFunctionsSample-HelloLambda-BuyStockLambda-000000000000",
            "Next": "Report Result"
        },
        "Sell Stock": {
            "Type": "Task",
            "Resource": "arn:aws:lambda:us-west-1:111122223333:function:StepFunctionsSample-HelloLambda-SellStockLambda-111111111111",
            "Next": "Report Result"
        },
        "Report Result": {
            "Type": "Task",
            "Resource": "arn:aws:states:::sns:publish",
            "Parameters": {
                "TopicArn": "arn:aws:sns:us-west-1:111122223333:StepFunctionsSample-HelloLambda1111-2222-3333-ReportResultSnsTopic-222222222222",
                "Message": {
                    "Input.$": "$"
                }
            },
            "End": true
        }
    }
}

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

IAM Examples

These example Amazon Identity and Access Management (IAM) policies generated by the sample project include 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.

{
    "Statement": [
        {
            "Action": [
                "lambda:InvokeFunction"
            ],
            "Resource": "arn:aws:lambda:us-west-1:111122223333:function:StepFunctionsSample-HelloLam-CheckStockPriceLambda-444455556666",
            "Effect": "Allow"
        }
    ]
}

{
    "Statement": [
        {
            "Action": [
                "lambda:InvokeFunction"
            ],
            "Resource": "arn:aws:lambda:us-west-1:111122223333:function:StepFunctionsSample-Hello-GenerateBuySellRecommend-123456789012",
            "Effect": "Allow"
        }
    ]
}

{
    "Statement": [
        {
            "Action": [
                "lambda:InvokeFunction"
            ],
            "Resource": "arn:aws:lambda:us-west-1:111122223333:function:StepFunctionsSample-HelloLambda-BuyStockLambda-777788889999",
            "Effect": "Allow"
        }
    ]
}

{
    "Statement": [
        {
            "Action": [
                "lambda:InvokeFunction"
            ],
            "Resource": "arn:aws:lambda:us-west-1:111122223333:function:StepFunctionsSample-HelloLambda-SellStockLambda-000000000000",
            "Effect": "Allow"
        }
    ]
}

{
    "Statement": [
        {
            "Action": [
                "sqs:SendMessage*"
            ],
            "Resource": "arn:aws:sqs:us-west-1:111122223333:StepFunctionsSample-HelloLambda4444-5555-6666-RequestHumanApprovalSqs-111111111111",
            "Effect": "Allow"
        }
    ]
}

{
    "Statement": [
        {
            "Action": [
                "sns:Publish"
            ],
            "Resource": "arn:aws:sns:us-west-1:111122223333:StepFunctionsSample-HelloLambda1111-2222-3333-ReportResultSnsTopic-222222222222",
            "Effect": "Allow"
        }
    ]
}

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