AWS Lambda returns empty response on RDS connect - NodeJS

Question

I have an AWS RDS which is publicly accessible and I want to connect to that RDS using AWS Lambda. I am using API Gateway to create a Rest API named "/hello", which needs to return the RDS connection status.

The Lambda code is given below.

var mysql = require('mysql');
var ApiBuilder = require('claudia-api-builder'),
  api = new ApiBuilder();

var con = mysql.createConnection({
  host: "host",
  user: "user",
  password: "password"
});

module.exports = api;

api.get('/hello', function () {

//any code written here, works perfectly, when this is called

  con.connect(function(err) { //this part doesn't work
    if (err) return err;
    return "connected";
  });
});

The database is publicly accessible, even from my local machine. The Lambda function also has the required permissions with AWS RDS.

The response I get on the browser is as follows

{}

I checked the cloud watch logs, and it is given below.

08:16:11
START RequestId: bf804be1-4797-11e8-8b3f-5b09118631a6 Version: $LATEST
08:16:11
END RequestId: bf804be1-4797-11e8-8b3f-5b09118631a6
08:16:11
REPORT RequestId: bf804be1-4797-11e8-8b3f-5b09118631a6  Duration: 34.28 ms  Billed Duration: 100 ms Memory Size: 128 MB Max Memory Used: 26 MB

The Lambda function doesn't go past con.connect(...) where there is no error being shown anywhere (not even on RDS logs). The API Gateway works, because any code before con.connect(...) works perfectly. What could be the issue here?

Answer 1

As @ConfusedCoder explained, this is caused due to con.connect(...) being an asynchronous call. Using the context in Lambda is not an option here, as Lambda is being invoked using API Gateway, and that there is no exports.myhandler being used in the scenario. Therefore the context object cannot be used to control the flow of Lamda.

exports.myHandler = function(event, context) {
   ...
} 

I tried playing with promises, async await and other techniques until I found a node package named sync-mysql. This makes synchronous queries to a mysql database, where AWS Lambda does not proceed without executing the database call. The updated code is given below, using 'sync-mysql'.

var ApiBuilder = require('claudia-api-builder'), api = new ApiBuilder();    
var MySql = require('sync-mysql');

var connection = new MySql({
  host: "host",
  user: "user",
  password: "password"
});

module.exports = api;

api.get('/hello', function(request) {    
  return connection.query('SELECT * FROM DB.DummyTable');    
});