Call to IAM API in Lambda times out - node.js

Question

I have a NodeJS lambda function that is trying to list IAM users via the IAM listUsers API method . The call is firing off but never returning until the lambda function itself times out and I'm unsure why. Here is the code:
exports.handler = async (event) => {
console.log('before call');
var ret = await listIAMUsers();
console.log('ret: ' + JSON.stringify(ret));
};
async function listIAMUsers() {
var AWS = require('aws-sdk');
AWS.config.update({region: 'REGION'});
var iam = new AWS.IAM({apiVersion: '2010-05-08'});
var params = {MaxItems: 10};
return iam.listUsers(params).promise();
}

Answer 1

Managing IAM Users. Pay close attention where we initialize the client and add require statements.
For the optimization purpose. it is good to load and initialize the. client while loading the function
// Load the AWS SDK for Node.js
var AWS = require('aws-sdk');
// Set the region
AWS.config.update({region: 'REGION'});
// Create the IAM service object
var iam = new AWS.IAM({apiVersion: '2010-05-08'});
As JS is single-threaded so you reuse the clients.
// Load the AWS SDK for Node.js
var AWS = require('aws-sdk');
exports.handler = async (event, context) => {
console.log('before call');
var ret = await listIAMUsers();
console.log('ret: ' + JSON.stringify(ret));
};
async function listIAMUsers() {
// Set the region
AWS.config.update({region: 'REGION'});
// Create the IAM service object
var iam = new AWS.IAM({apiVersion: '2010-05-08'});
var params = {MaxItems: 10};
return iam.listUsers(params).promise();
}
START RequestId: 933ca3dd-2feb-4f98-8f8e-87286f59748d Version: $LATEST
2021-02-22T15:57:14.867Z 933ca3dd-2feb-4f98-8f8e-87286f59748d INFO before call
2021-02-22T15:57:15.560Z 933ca3dd-2feb-4f98-8f8e-87286f59748d INFO ret: {"ResponseMetadata":{"RequestId":"bf65a9f5-e4a6-493b-a6a2-c3081d88f7be"},
"Users":[
{"Path":"/","UserName":"username","UserId":"sadsadsadsa",
"Arn":"arn:aws:iam::1234567890:user/username",
"CreateDate":"2020-11-27T13:09:20.000Z","Tags":[]},
{"Path":"/","UserName":"tempuser","UserId":"adsadasdasdsad",
"Arn":"arn:aws:iam::1234567890:user/tempuser",
"CreateDate":"2021-01-24T21:24:47.000Z","Tags":[]}],"IsTruncated":false}
END RequestId: 933ca3dd-2

Answer 2

There are a few possibilities here:
Lambda Role Permission - Try to check if your lambda role is attached with the correct IAM Policy such as arn:aws:iam::aws:policy/IAMReadOnlyAccess
If your Lambda function is placed within a Public Subnet or Private Subnet without any internet access, you would require arn:aws:iam::aws:policy/service-role/AWSLambdaVPCAccessExecutionRole attached as well as the internet or aws services access (shown here)