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Facilitate using cluster and domain modules, live reload application in development mode on code change.


master-cluster is a utility to facilitate implementing node.js core cluster module in any project. I created this module as I use the cluster module in pretty much all my projects and wanted to remove the boilerplate code. It implements node.js core domain module for correct exception handling. It also provides hot reloading of files on the worker in development mode so that workers are restarted when code is changed.

In boot.js:

var MC = require('master-cluster')
  , worker = require.resolve('./server.js');
MC.start({exec: worker});

In server.js:

var MC = require('master-cluster')
  , app = require('./app.js')
  , http = require('http');

// set the handler that will be used for all new requests
MC.setFnHandlers(app.index, shutdown);

// create the server and pass MC run handler
// each request will be wrap in a domain for exception handling
// so that workers are restarted automatically on crash
var server = http.createServer(;
server.listen(3000, function () {
  console.log("Listening on %d", 3000);

function shutdown () {
    // optional - cleanly close db connections and other resources

In app.js:

function index (req, res) {
    // do something with the request and response

exports.index = index;

The code above can be simplified if all you need is to start a http server.

In server.js:

var MC = require('master-cluster')
  , app = require('./app.js');

MC.createHttpServer(app.index, 3000, shutdown);

function shutdown () {
    // cleanly close db connections and other resources
var app = require('express')();
var MC = require('master-cluster');
var responseTime = require('response-time');
// setup middlewares, mount routes, etc. 
app.use(responseTime({ header: 'x-response-time' }));
app.get('/', function (req, res) {
  res.end('Hello world');
MC.createHttpServer(app, 3000);
console.log('Server listening on %d', 3000);

Following options can be passed to the master cluster configuration:

  • exec: the code to run on the cluster master
  • size: the number of workers to start, default is require("os").cpus().length
  • reload: boolean, default is false except when process.env.NODE_ENV == 'dev'
  • logger: optional logger for errors (must implement error method)

Reloader specific options:

  • cooldown: number of milliseconds to wait between file changes, default is 100ms
  • extensions: file extensions to watch for and reload on change, default to js

Worker options:

  • killTimeout: timeout to kill the worker on uncaught exception (default 30s)
  • logger: optional logger for errors (must implement error method)
  • start (options): start the master with cluster options
  • run (): worker http handler that runs the request wrapped in the domain error handling
  • setFnHandlers (runFn, errorFn): set the run and error handlers for the domain module
  • setOptions (options): set the options for the workers (logger and kill timeout)
  • createHttpServer (handler, port, onShutdown): create the http server and setup the run and error handlers for the domain module
  • cluster: expose the exported cluster module


This module is still experimental and subject to change. Please open issues for bugs and suggestions in github. Pull requests welcome.

Jerome Touffe-Blin, @jtblin,

master-cluster is copyright 2013 Jerome Touffe-Blin and contributors. It is licensed under the BSD license. See the include LICENSE file for details.