Reusing Mysql Connection in Lambda on AWS - mysql

Question

I have a lot of lambda invocations and I am always querying database so I want my lambda to be able to reusing connection, so I am establishing connection in constructor, like this:
let mysqlConnection = mysql.createConnection({
host: process.env.HOST,
user: process.env.DB_USER,
password: process.env.BDB_PWD,
port: process.env.DB_PORT,
database: process.env.DB_NAME
});
dbConn.connect(function(err) {
if (err) {
throw new Error('Error during connecting to db');
} else {
console.log("Database is connected");
}
});
And I have callbackWaitsForEmptyEventLoop set to false in my handler:
exports.handler = (event, context) => {
context.callbackWaitsForEmptyEventLoop = false;
event.Records.forEach(record => {
processEvent(JSON.parse(record.body), context);
});
};
When mysql connection fails I am destroying mysql connection, my query in provessEvent function looks like this:
mysqlConnection.query(sql, values, function (err, rows) {
if (err) {
mysqlConnection.destroy();
context.fail();
}
}
But I am getting a lambda errrors from time to time. I guess sometimes lambda wants to reuse a connection which is not available.
"Error: Error during connecting to db",
" at Handshake.<anonymous> (/var/task/lambda.js:34:13)",
" at Handshake.<anonymous> (/var/task/node_modules/mysql/lib/Connection.js:525:10)",
" at Handshake._callback (/var/task/node_modules/mysql/lib/Connection.js:491:16)",
" at Handshake.Sequence.end (/var/task/node_modules/mysql/lib/protocol/sequences/Sequence.js:83:24)",
" at Protocol.handleNetworkError (/var/task/node_modules/mysql/lib/protocol/Protocol.js:369:14)",
" at Connection._handleNetworkError (/var/task/node_modules/mysql/lib/Connection.js:421:18)",
" at Connection._handleConnectTimeout (/var/task/node_modules/mysql/lib/Connection.js:417:8)",
" at Object.onceWrapper (events.js:286:20)",
" at Socket.emit (events.js:198:13)",
" at Socket.EventEmitter.emit (domain.js:448:20)"
Is there anything could I do to prevent this situation? Or should I destroy connection and connect once again?

Answer 1

I found this useful tool that could help you, https://github.com/jeremydaly/serverless-mysql you need just to install a npm module and configure it. Check also the #connection-backoff section.

Answer 2

I do not use MySQL but Mongodb in some projects. callbackWaitsForEmptyEventLoop was help.
'use strict';
const mysql = require('mysql'); // require mysql
// If 'client' variable doesn't exist
if (typeof client === 'undefined') {
// Connect to the MySQL database
var client = mysql.createConnection({
// your connection info
});
client.connect()
}
module.exports.handler = (event, context, callback) => {
// This will allow us to freeze open connections to a database
context.callbackWaitsForEmptyEventLoop = false;
client.query('SELECT * FROM `books`', function (error, results) {
callback(null, results)
});
}
Refer to AWS document and this tutorial