Lambda function for promoting replica to master

index.js

var AWS = require('aws-sdk');
AWS.config.update({ region: 'your-region-ie:eu-central-1' });
var mysql = require('mysql');

// Better to use environment variables, but for the example we'll leave it like this

var dbClusterIdentifier = 'your-cluster';
var clusterEndpoint = 'your-cluster.cluster-identifier.your-region.rds.amazonaws.com';
var user = 'username';
var password = 'password';
var database = 'database';

exports.handler = (event, context, callback) => {
    
    // Initialize new RDS object
    var rds = new AWS.RDS();

    // Connect to the MySQL Instance

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

    var master;
    var replica;

    con.connect(function (err) {
      	if (err) console.log(err) && context.fail();
        console.log('Conneting to database...');

        con.query("select server_id from mysql.ro_replica_status where session_id <> 'MASTER_SESSION_ID' order by current_replay_latency_in_usec desc;", function (err, result, fields) {
            if (err) console.log(err) && context.fail();
            replica = result[0].server_id;
            console.log('trying to promote instance ' + replica + ' to cluster...')

            var params = {
                DBClusterIdentifier: dbClusterIdentifier,
                TargetDBInstanceIdentifier: replica
            };
            rds.failoverDBCluster(params, function (err, data) {
                if (err) console.log(err, err.stack) && context.fail(); // an error occurred
                else console.log(data) && console.log('instance ' + replica + ' + was successfully promoted to cluster.') && context.succeed('Success'); // successful response
            });
        });
    })
};