Aws Pass Value from Lambda Trigger to Step Function

Question

When using a Lambda Function to trigger a Step Function, how do you get the output of the function that triggered it?

Do you want to pass said output to the Step Function or somewhere else ? — ElFitz, Aug 29 '18 at 14:42

score 0 · Answer 1 · answered Aug 31 '18 at 00:07

Ok, so if you want to pass an input to a Step Function execution (or, more exactly, your 'State Machine''s execution), you just need to set said input the input property when calling StartExecution (see AWS Documentation: Start Execution)

In your case, it would most likely be your lambda's last step before calling it's callback.

If it's a node js lambda, that's what it would look like

const AWS = require("aws-sdk");
const stepfunctions = new AWS.StepFunctions();

exports.myHandler = function(event, context, callback) {

    ... your function's code

    const params = {
       stateMachineArn: 'YOUR_STATE_MACHINE_ARN', /* required */
       input: 'STRINGIFIED INPUT',
       name: 'AN EXECUTION NAME (such as an uuid or whatever)'
    };
    stepfunctions.startExecution(params, function(err, data) {
       if (err) callback(err); // an error occurred
       else     callback(null, "some success message"); // successful response
    });

}

Alternatively, if your payload is too big, you could store the data in S3 or DynamoDB and pass the reference to it as your State Machine's execution's input.

Aws Pass Value from Lambda Trigger to Step Function

1 Answers1