Why does my await lambda.invoke function invoke lambda multiple times?

Question

Currently

I have a lambdaX that invokes another lambdaY.

Lambda X:

"use strict";

const AWS = require('aws-sdk');
AWS.config.region = 'ap-southeast-2';
var lambda = new AWS.Lambda();

exports.handler = async (event) => {

  //the final return
  var dataToSave = []

  //data to be added to array
  let returnLoad;

  var params = {
    FunctionName: 'lambdaY', // the lambda function we are going to invoke
    InvocationType: 'RequestResponse',
    LogType: 'Tail', //Set to Tail to include the execution log in the response.
  };

  try {
    await lambda.invoke(params, function(err, data) {
      if (err) {
        console.log("Error");
        console.log(err, err.stack);
      } else {
        console.log("Success");
        console.log(data);
        returnLoad = data.Payload;
      }
    }).promise();

    dataToSave.push(returnLoad);

  } catch (err) {
      console.log('some error occurred...');
  }

  const response = {
      statusCode: 200,
      body: JSON.stringify(dataToSave)
  };
  return response;
}

Lambda Y:

exports.handler = async (event) => {
    const response = {
        statusCode: 200,
        body: JSON.stringify('Hello from Lambda!'),
    };
    return response;
};

Problem

For some reason lambdaY invokes 2+ times whenever I invoke lambdaX. Note, lambdaX gets the correct response back, but I want to avoid unnecessarily invoking lambdaY multiple times.

What do I need to change in my code? (or lambda configuration)

Logs:

Note: 2 logs of lambdaY being invoked at exactly the same time.

Note: LambdaX results are healthy and as expected. There isn't a duplicate log.

Have you confirmed that lambdaY is being initiated by lambdaX both times? For example the event that's triggering lambdaX might also be triggering lambdaY due to a configuration issue. Maybe try logging the payload of lambdaY to confirm it's coming from lambdaX. — j-petty
– j-petty, Commented Feb 2, 2020 at 23:18
Additionally, have you check the logs to ensure lambdaX is only being triggered once? — j-petty
– j-petty, Commented Feb 2, 2020 at 23:19
@jpetty, yes, the logs of lambdaX show it is only being triggered once, and logs of lambdaY show payload coming from X (when I have included a payload to test that question) — Wronski
– Wronski, Commented Feb 2, 2020 at 23:23
Thanks @Wronski, typically seeing duplicate lambda invocations would be caused by failure retries. lambdaY might be failing causing lambdaX to retry. What's in the logs of lambdaX? Does it get a successful response back from lambdaY? — j-petty
– j-petty, Commented Feb 2, 2020 at 23:40
@jpetty, I have added logs for lambdaX. They were as expected and showing no errors. — Wronski
– Wronski, Commented Feb 2, 2020 at 23:48

jarmod · Accepted Answer · 2022-11-17 21:34:47Z

Your code is misusing the AWS SDK. Specifically, it is using both the callback and promise features simultaneously. It should use one or the other, but not both.

I would change it to use just the promise (and obviously add some error handling to this):

const data = await lambda.invoke(params).promise();
const returnLoad = data.Payload;

The reason that lambda.invoke(params, callback).promise() sends 2 requests is as follows:

within the AWS SDK generally, a call to service.action(params) returns an AWSRequest object on which you have to call .send() for the API request to actually be sent
a call to service.action(params, callback) executes the following code: if (callback) request.send(callback), so the presence of the callback function sends the API request
the .promise() method's code "sends the request and returns a promise", so it also sends the API request

And that's why the API call happens twice if callback and promise() are both present.

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