Node function in AWS Lamda timing out

Question

I'm trying to call a lamda function writen in Node.JS hosted in the SAM local environment. The function is connecting to a locally hosted MySQL database.

The code is as follows:

var mysql = require('mysql');

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

    let id =  (event.pathParameters || {}).division || false;

    var con = mysql.createConnection({
        host: "host.docker.internal",
        user: "root",
        password: "root",
        database: "squashprod"
    });

    switch(event.httpMethod){

        case "GET":

                con.connect(function(err) {
                    if (err) throw err;
                    con.query("SELECT * FROM players where division_id = 1",
                        function (err, result, fields) {
                            if (err) throw err;
                            //console.log(result);
                            return callback(null, {body: "This message does not work"});
                        }
                    );
                });

//                  return callback(null, {body: "This message works"});

                break;


        default:
            // Send HTTP 501: Not Implemented
            console.log("Error: unsupported HTTP method (" + event.httpMethod + ")");
            callback(null, { statusCode: 501 })

    }

}

However the callback (with the message "This message does not work") is not coming out. I know it's calling the DB as the console.log call prints the result. When this code runs I get an internal server error in the browser and the following messages from SAM Local:

2018-09-13 20:46:18 Function 'TableGetTest' timed out after 3 seconds
2018-09-13 20:46:20 Function returned an invalid response (must include one of: body, headers or statusCode in the response object). Response received: b''
2018-09-13 20:46:20 127.0.0.1 - - [13/Sep/2018 20:46:20] "GET /TableGetTest/2 HTTP/1.1" 502 -
2018-09-13 20:46:20 127.0.0.1 - - [13/Sep/2018 20:46:20] "GET /favicon.ico HTTP/1.1" 403 -

If I comment out the call to the DB and just go with the callback that says, "This message works" then there is no timeout and that message appears in the browser

I know the DB code is sound as it works standalone. I feels it's got something to do with the callback but I don't know Node well enough to understand.

I'm pulling what little hair I've got out. Any help would be greatly appreciated!

Answer 1

I had the same problem and here is how I solved it.

First problem is time is not enough for cold start.

Increase the execution time of your lambda. Initial connection setup will take longer time.

Further,

You need to close the connection once you are done with the query. Otherwise it will not keep the event loop of node empty which make the lambda assume still it is in the work.

Resolved with two ways:

1. Close all the connection as soon as everything is complete.
2. Use Sequelize rather than plan mysql library. Sequelize will help to maintain connection pools and share across connections.

https://www.npmjs.com/package/sequelize

Hope it helps.