How to Use Node Cluster module within Express Generator App Skeleton

Question

I am trying to use the cluster module within my Express app. I used express-generator to create my application structure, but I am not sure how to incorporate the cluster module while maintaining the separation of app.js and bin/www. I have seen tutorials and github examples of using cluster with express, but none in a full application skeleton. Is there a way to maintain the separation of app.js and www while incorporating the cluster module?

Here is my full bin/www file:

#!/usr/bin/env node

/**
 * Module dependencies.
 */

var app = require('../app');
var debug = require('debug')('football:server');
var http = require('http');
var cluster = require('cluster');
var numCPUs = require('os').cpus().length;

/**
 * Get port from environment and store in Express.
 */

var port = normalizePort(process.env.PORT || '3000');
app.set('port', port);

if(cluster.isMaster){
  // Fork workers.
  for (var i = 0; i < numCPUs; i++) {
    console.log('forking process', i)
    cluster.fork();
  }

  // If a worker dies, log it to the console and start another worker.
  cluster.on('exit', function(worker, code, signal) {
    console.log('Worker ' + worker.process.pid + ' died.');
    cluster.fork();
  });

  // Log when a worker starts listening
  cluster.on('listening', function(worker, address) {
    console.log('Worker started with PID ' + worker.process.pid + '.');
  });
}
else{
  /**
   * Create HTTP server.
   */
   console.log('i am in the else statement')
  var server = http.createServer(app);
  console.log('created another server')
  /**
   * Listen on provided port, on all network interfaces.
   */

  server.listen(port);
  server.on('error', onError);
  server.on('listening', onListening);
}

/**
 * Normalize a port into a number, string, or false.
 */

function normalizePort(val) {
  var port = parseInt(val, 10);

  if (isNaN(port)) {
    // named pipe
    return val;
  }

  if (port >= 0) {
    // port number
    return port;
  }

  return false;
}

/**
 * Event listener for HTTP server "error" event.
 */

function onError(error) {
  if (error.syscall !== 'listen') {
    throw error;
  }

  var bind = typeof port === 'string'
    ? 'Pipe ' + port
    : 'Port ' + port;

  // handle specific listen errors with friendly messages
  switch (error.code) {
    case 'EACCES':
      console.error(bind + ' requires elevated privileges');
      process.exit(1);
      break;
    case 'EADDRINUSE':
      console.error(bind + ' is already in use');
      process.exit(1);
      break;
    default:
      throw error;
  }
}

/**
 * Event listener for HTTP server "listening" event.
 */

function onListening() {
  var addr = server.address();
  var bind = typeof addr === 'string'
    ? 'pipe ' + addr
    : 'port ' + addr.port;
  debug('Listening on ' + bind);
  console.log('yay')
}

I never get the message saying that "Worker is listening with pid..." and the console.log() at the top of the else statement never gets printed.

Answer 1

This is the full express-generator bin/www file with cluster support:

#!/usr/bin/env node

/**
 * Module dependencies.
 */

var app = require('../app');
var cluster = require('cluster');
var debug = require('debug')('temp:server');
var http = require('http');
var numCPUs = require('os').cpus().length;

/**
 * Get port from environment and store in Express.
 */

var port = normalizePort(process.env.PORT || '3000');
app.set('port', port);

if (cluster.isMaster) {
  // Fork workers.
  for (var i = 0; i < numCPUs; i++) {
    cluster.fork();
  }

  // If a worker dies, log it to the console and start another worker.
  cluster.on('exit', function(worker, code, signal) {
    console.log('Worker ' + worker.process.pid + ' died.');
    cluster.fork();
  });

  // Log when a worker starts listening
  cluster.on('listening', function(worker, address) {
    console.log('Worker started with PID ' + worker.process.pid + '.');
  });

} else {
  /**
   * Create HTTP server.
   */

  var server = http.createServer(app);

  /**
   * Listen on provided port, on all network interfaces.
   */

  server.listen(port);
  server.on('error', onError);
  server.on('listening', onListening);
}

// The rest of the bin/www file.....

/**
 * Normalize a port into a number, string, or false.
 */

function normalizePort(val) {
  var port = parseInt(val, 10);

  if (isNaN(port)) {
    // named pipe
    return val;
  }

  if (port >= 0) {
    // port number
    return port;
  }

  return false;
}

/**
 * Event listener for HTTP server "error" event.
 */

function onError(error) {
  if (error.syscall !== 'listen') {
    throw error;
  }

  var bind = typeof port === 'string'
    ? 'Pipe ' + port
    : 'Port ' + port;

  // handle specific listen errors with friendly messages
  switch (error.code) {
    case 'EACCES':
      console.error(bind + ' requires elevated privileges');
      process.exit(1);
      break;
    case 'EADDRINUSE':
      console.error(bind + ' is already in use');
      process.exit(1);
      break;
    default:
      throw error;
  }
}

/**
 * Event listener for HTTP server "listening" event.
 */

function onListening() {
  var addr = server.address();
  var bind = typeof addr === 'string'
    ? 'pipe ' + addr
    : 'port ' + addr.port;
  debug('Listening on ' + bind);
}

You should be able to use this file as a drop in replacement for the existing bin/www file. No other changes to your existing application or third party modules are required.