db.js

var mysql = require('mysql');

var db_config = {
    host     : '127.0.0.1', // Your host - either local or cloud
    user     : 'root', // your username
    password : 'root', // your password
    database : 'your-db-name' // database name
};

var connection;

function handleDisconnect() {
    connection = mysql.createConnection(db_config); // Recreate the connection, since
                                                    // the old one cannot be reused.

    connection.connect(function(err) {              // The server is either down
        if(err) {                                     // or restarting (takes a while sometimes).
            console.log('error when connecting to db:', err);
            setTimeout(handleDisconnect, 2000); // We introduce a delay before attempting to reconnect,
        }                                     // to avoid a hot loop, and to allow our node script to
    });                                     // process asynchronous requests in the meantime.
                                            // If you're also serving http, display a 503 error.
    connection.on('error', function(err) {
        console.log('db error', err);
        if(err.code === 'PROTOCOL_CONNECTION_LOST') { // Connection to the MySQL server is usually
            handleDisconnect();                         // lost due to either server restart, or a
        } else {                                      // connnection idle timeout (the wait_timeout
            throw err;                                  // server variable configures this)
        }
    });
}

handleDisconnect();

module.exports = connection;