cluster.js

var express = require('express');
var cluster = require('cluster');

if (cluster.isMaster) {
  var _cpus = require('os').cpus().length;
  // create a worker for each CPU
  for (var i = 0; i < _cpus; i += 1) {
      cluster.fork();
  }
  // When a worker dies create another one
  cluster.on('exit', function(worker) {
    console.log('worker ' + worker.id +  ' died');
    cluster.fork();
  });
} else {
  // create a new Express application
  var app = express();
  app.get('/', function (req, res) {
      res.send('Hello World');
  });

  // bind to a port
  app.listen(3000);
}