invoking lambda from other lambda - amazon-web-services

Question

In our system we have a flow of Lambdas calling other Lambdas based on results they get.
This flow will probably be refactor to use the AWS step function in the future but will probably stay as it is for the next month or two.
Recently a new lambda has been introduced, and we're encountering a problem:
if we test our Lambda function 1 locally, it properly calls function 2 on AWS.
However, after deploying the lambda and running the same test, function doesn't get called (there's no invocation in the monitoring chart)
here's a code example of Function 1:
'use strict';
const AWS = require("aws-sdk");
const lambda = new AWS.Lambda({ region: "eu-west-1" });
const myHandler = async (event, _, callback) => {
console.log(event)
return doSomething()
.then(something)
.then(somethingElse)
.catch(handleError)
function doSomething() {
return fetch('someurl.com');
}
function something(r) {
if(r.status === 204) {
let lambdaRes = callLambda( "LambdaB", { foo: bar } );
console.log(lambdaRes)
}
return r
}
somethingElse(r) {
if(r.status === 500) {
throw new Error(`bar`);
}
return r.json()
}
async function callLambda(fnName, payload ) {
let params = {
FunctionName: fnName,
InvocationType: 'Event',
Payload: JSON.stringify(payload)
}
return await lambda.invoke(params);
}
function handleError(e) {
if(e.message === 'bar') {
let lambdaRes = callLambda( "LambdaC", { bar: 'foo' } );
console.log(lambdaRes)
}
return callback(null, { message: `Completed with error`});
}
exports.handler = myHandler;
We tried to check if the problem was caused by authorization and tested by providing ALL authorization possible to function 1 but with no results.
Any suggestion?
UPDATE:
Both Function use the same
VPC: vpc-hashnumberVpc,
Subnets: [ subnet-hashnumber1 , subnet-hashnumber2 , subnet-hashnumber3 ]
Security Group: sg-hashnumberSg

Answer 1

When the first Lambda function calls lambda.invoke() it is not somehow connecting to the other Lambda function inside the VPC. At that point there is no running instance of the other Lambda function, only the definition of it exists. What is happening is lambda.invoke() makes a call to the AWS API which is on the public Internet, requesting that AWS create a new invocation of the second function.
Lambda functions running inside a VPC do not get public IP addresses assigned to them, even if they are in a public subnet. The only way to give a Lambda function inside a VPC access to the Internet is to place the Lambda function in a private subnet with a route to a NAT Gateway.
Alternatively, you can configure an AWS Lambda VPC Endpoint, which gives resources inside your VPC access to call the AWS Lambda API without going over the Internet.
So in order for a Lambda function running inside a VPC to make AWS API calls to invoke other Lambda functions, your options are to add a NAT Gateway to the VPC, or add an AWS Lambda VPC Endpoint to the VPC.

Answer 2

So if function 1 is able to call function 2 locally, I think the problem is with networking/AWS setup, here are a few things you can do :
Set up Log/Print statements at every level, so you can pinpoint which line is returning an error.
Is the function timing out? If so check the timeout and Memory Allocated to the function, if the function is memory intensive it will not complete.
Last but very important , check your network/Subnets, if you have configured lambda to be running on multiple subnets, choose one of them and try, look at the VPC, perhaps the Lambda is not attached to any VPC or check if the attached vpc is able to connect to the other lambda, have a look at Security Groups as well.
Most of my lambda issues are resolved with this, all the best.