Reproduce MySQL error: The server closed the connection (node.js)

Question

I\'m trying to reproduce a MySQL error I\'m seeing in my node.js app on EC2 with the node mysql library:

Connection lost: The server closed the connec

Answer 1

I was having similar problems and created a getConnection() wrapper function that checks the health of the mysql connection before returning it to the caller and re-establishes the connection as necessary. In my testing it has handled fatal and non-fatal connection issues transparently for the application. If the connection simply timed out, the application recovers without experiencing any errors. If there is a transient but fatal database connection problem, the application will resume functioning automatically as soon as database connectivity is available again.

As far as reproducing the problem for testing, add the following two lines to the my.ini or my.cnf file under the [mysqld] block:

interactive_timeout=30
wait_timeout=30

Here is the contents of a file I have named "database.js":

var mysql = require("mysql");
var CONFIG = require(__dirname + "/configuration");

module.exports.getConnection = function() {
    // Test connection health before returning it to caller.
    if ((module.exports.connection) && (module.exports.connection._socket)
            && (module.exports.connection._socket.readable)
            && (module.exports.connection._socket.writable)) {
        return module.exports.connection;
    }
    console.log(((module.exports.connection) ?
            "UNHEALTHY SQL CONNECTION; RE" : "") + "CONNECTING TO SQL.");
    var connection = mysql.createConnection({
        host     : CONFIG.db.host,
        user     : CONFIG.db.user,
        password : CONFIG.db.password,
        database : CONFIG.db.database,
        port     : CONFIG.db.port
    });
    connection.connect(function(err) {
        if (err) {
            console.log("SQL CONNECT ERROR: " + err);
        } else {
            console.log("SQL CONNECT SUCCESSFUL.");
        }
    });
    connection.on("close", function (err) {
        console.log("SQL CONNECTION CLOSED.");
    });
    connection.on("error", function (err) {
        console.log("SQL CONNECTION ERROR: " + err);
    });
    module.exports.connection = connection;
    return module.exports.connection;
}

// Open a connection automatically at app startup.
module.exports.getConnection();

// If you've saved this file as database.js, then get and use the
// connection as in the following example:
// var database = require(__dirname + "/database");
// var connection = database.getConnection();
// connection.query(query, function(err, results) { ....