Return data from invoked AWS Lambda

Question

How can I invoke a lambda function from another lambda and get the response data back into the original function to continue processing that data? I have the main lambda function (A) in Node.js, and the second lambda function (B) that is in python. Here is what I need:

1. lambda A (node.js) invokes lambda B and passes arguments to it
2. lambda B (python) processes the arguments and generates a response in JSON
3. lambda A receives the response and does more processing
4. lambda A generates a JSON return/response

Not to burden you with my code, here is a simple example of what I'm trying to do.

Lambda A

AWS.config.region = 'us-east-2';
var lambda = new AWS.Lambda();

var dataPayloadCopy = 'BLANK';


exports.handler = function(event, context){
  var params = {
    FunctionName: 'arn:aws:lambda:us-east-2:958569232013:function:lambdaB', 
    InvocationType: 'RequestResponse',
    LogType: 'Tail',
    Payload: '{ "name" : "Adam" }'
  };

  var  lambdaResponse = lambda.invoke(params, function(err, data) {
    if (err) {
      console.log("error");
    } else {
      console.log("Response inside callback function: \n" + JSON.stringify(data.Payload));
      //console.log(data.Payload);
      dataPayloadCopy = data.Payload;
    }
  });
  
  console.log("  ------  ");
  console.log("Global response data copy: " + JSON.stringify(dataPayloadCopy));
  console.log("  ------  ");
  console.log("lambdaResponse data: ");
  console.log(lambdaResponse.response.data);
  console.log("  ------  ");
  
  return {
        'statusCode': 200,
        'body': JSON.stringify({"message":"life is good"}),
        'headers': {
            'Content-Type': 'application/json; charset=utf-8',
            'Access-Control-Allow-Origin': '*'
        },
    }
  
}; 

Lambda B

import json
 
def lambda_handler(event,context):
    
    responseMessage = {"message":"Arguments received: name: " + event['name']}
    return {
        'statusCode': 200,
        'body': json.dumps(responseMessage)
    }

Steps 1 and 2 work with no problem. I can't accomplish step 3. I see the lambda B response in the data.Payload in the lambda.invoke() callback function and can print it out there, but how can I get that value into the main lambda A function so I can work with it there? I tried to copy data.Payload into a global variable dataPayloadCopy, and also assign lambda.invoke() value to lambdaResponse variable (in code above). Neither way worked. Looks like the lambda B executes when lambda A finishes.

Here is the execution result:

INFO      ------  
INFO    Global response data copy: "BLANK"
INFO      ------  
INFO    lambdaResponse data: 
INFO    null
INFO      ------  
INFO    Response inside callback function: 
"{\"statusCode\": 200, \"body\": \"{\\\"message\\\": \\\"Arguments received: name: Adam\\\"}\"}"

Also, I don't see the lambda A return value in the test results. If I change the handler function in lambda A to be asynchronous exports.handler = async (event) => { and run a test, lambda A return value shows, but there is no printout from the callback function appears as if lambda B was not invoked and/or the return was not received.

I did not have any problem with a similar task if both lambdas are in python. My lambda A code is in Node.js though.

Answer 1

The Lambda invoke function is asynchronous and uses callbacks. Hence, while your invoke is calling the Python Lamdda function, the rest of your code outside of the callback is continuing to run.

The best approach for you would be to change the next steps of your code inside of the callback function like below,

AWS.config.region = "us-east-2";
var lambda = new AWS.Lambda();

var dataPayloadCopy = "BLANK";

exports.handler = function (event, context) {
  var params = {
    FunctionName: "arn:aws:lambda:us-east-2:958569232013:function:lambdaB",
    InvocationType: "RequestResponse",
    LogType: "Tail",
    Payload: '{ "name" : "Adam" }',
  };

  var lambdaResponse = lambda.invoke(params, function (err, data) {
    if (err) {
      console.log("error");
    } else {
      console.log(
        "Response inside callback function: \n" + JSON.stringify(data.Payload)
      );
      //console.log(data.Payload);
      dataPayloadCopy = data.Payload;
    }
  });
};