Callback Pattern Example (Amazon SQS, Amazon SNS, Lambda)

This sample project demonstrates how to have Amazon Step Functions pause during a task, and wait for an external process to return a task token that was generated when the task started.

When this sample project is deployed and an execution is started, the following steps occur:

To learn how to implement the callback pattern in Step Functions, see Wait for a Callback with the Task Token.

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

Step 1: Create the state machine and provision resources

Step 2: Run the state machine

Lambda Callback Example

To see how the components of this sample project work together, see the resources that were deployed in your Amazon account. For example, here is the Lambda function that calls Step Functions with the task token.

console.log('Loading function');
const aws = require('aws-sdk');

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

    for (const record of event.Records) {
        const messageBody = JSON.parse(record.body);
        const taskToken = messageBody.TaskToken;

        const params = {
            output: "\"Callback task completed successfully.\"",
            taskToken: taskToken
        };

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

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