AWS Lambda function with two callbacks

Question

at present I am doing a lambda function in node.js to get information of my AWS account. I have an issue when I want to retrieve the information required in the function. I see the information in the console (console.log) but it is not present in the response by callback(). I always get response of first callback and not of second. I have read about the asynchronous process but I don't achieve fix the issue. Do you know what is the change to improve the code?

The code is the next:

var AWS = require('aws-sdk');
var iam = new AWS.IAM();
var s3 = new AWS.S3();
exports.handler = (event, context, callback) => {
    var params1 = {};
 iam.listUsers(params1, function(err, data) {
   if (err)
    console.log(err, err.stack);
   else
    console.log(data);
    callback(null, data.Users);
 });
 var params2 = {};
 s3.listBuckets(params2, function(err, data) {
   if (err)
      console.log(err, err.stack);
   else
      console.log(data);
      callback(null, data.Buckets);
 });
};

Thanks in advance.

Yes, I want both results: iam users and s3 buckets. In the future I want to add: instances, security groups, subnet, etc. — Arsenio Aguirre
– Arsenio Aguirre, Commented Apr 1, 2018 at 19:35
you could also use Python, Java or C# to write your AWS Lambda function. Might be easier if you are already good at one of those. — mostafazh
– mostafazh, Commented Apr 1, 2018 at 20:21

mostafazh · Accepted Answer · 2018-04-17 20:54:55Z

4

Since AWS Lambda now supports node 8, an example code can be found below:

const AWS = require('aws-sdk');
const iam = new AWS.IAM();
const s3 = new AWS.S3();

async function stackoverflow() {
 let params1 = {};
 let params2 = {};

 try {
  // synchronously call each method and store resolved promises. 
  let results1 = await iam.listUsers(params1).promise();
  let results2 = await s3.listBuckets(params2).promise();

  console.log(results1);
  console.log(results2);
 }
 catch(e) {
  console.error(e);
 }
}

exports.handler = (event, context, callback) => {
  stackoverflow();
};

edited Apr 17, 2018 at 20:54

answered Apr 1, 2018 at 19:59

mostafazh

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7 Comments

Arsenio Aguirre Over a year ago

Thanks for your help, I have tested the code and it shows the error:"errorMessage": "Cannot find module 'async'"

mostafazh Over a year ago

you need to run npm install async and zip + upload everything (js file + the node_modules directory) to s3 and then deploy that s3 file as a new version. Please note that you still need to add "exports.handler = stackoverflow;" at the end of the code snippet and also remove the last 3 lines I've added for testing purposes.

Arsenio Aguirre Over a year ago

Hi, Lamba now supports node.js 8.10 and node.js 8.10 supports async/await, how would it be the code with async/await functions? Thanks in advance.

mostafazh Over a year ago

@aaaguirrep code updated. sorry for taking me this long :(

Arsenio Aguirre Over a year ago

Thanks for your time, I have tested the code and it shows the error: ""errorMessage": "Handler 'handler' missing on module 'index'"". In the console.log the results are ok. Any suggestions for fix the issue?

|

Paul · Accepted Answer · 2018-04-01 19:40:59Z

0

This is the ideal case for the Async library or Promise.all if you're using promises. I'll try and make a code sample later when I'm not on my mobile phone, but essentially they'll both let you execute several Async functions and then do one callback.

answered Apr 1, 2018 at 19:40

Paul

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1 Comment

Arsenio Aguirre Over a year ago

Thanks for your help. Could be that async is not supported for AWS Lambda because Lambda has 6.10 node.js version?

Khalid T. · Accepted Answer · 2018-04-01 22:06:01Z

Using Promise.all, you could do something like this:

const AWS = require("aws-sdk");

const iam = new AWS.IAM({apiVersion: "2010-05-08"});
const s3 = new AWS.S3({apiVersion: "2006-03-01"});

exports.handler = (event, context, callback) => {
    const iamParams = {};
    const s3Params = {};
    const promises = [listUsers(iamParams), listBuckets(s3Params)];

    // NOTE: If any of the passed-in promises reject, `Promise.all` asynchronously
    // rejects with the value of the promise that rejected,
    // whether or not the other promises have resolved.
    Promise.all(promises)
        .then(([users, buckets]) => {
            // console.log(users);
            // console.log(buckets);
            callback(null, {
                Users: users,
                Buckets: buckets
            });
        })
        .catch((err) => {
            callback(err);
        });
};

function listUsers(params) {
    return new Promise((resolve, reject) => {
        iam.listUsers(params, (err, data) => {
            if (err) {
                reject(err);
            } else {
                resolve(data.Users);
            }
        });
    });
}

function listBuckets(params) {
    return new Promise((resolve, reject) => {
        s3.listBuckets(params, (err, data) => {
            if (err) {
                reject(err);
            } else {
                resolve(data.Buckets);
            }
        });
    });
}

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