How to setup clusters in expressjs 4.x app?

Question

I have an expressjs generated app which is configured with socket io and I would like to implement nodejs clusters in it. The problem is that in Express 4.x the server listening configuration is in the bin/www file and no longer in app.js file. Also my app is configured with socket io so I don't want to brake it too.

This is how it should be implemented in express apps according to this article:

app.js

// Include the cluster module
var cluster = require('cluster');

// Code to run if we're in the master process
if (cluster.isMaster) {

    // Count the machine's CPUs
    var cpuCount = require('os').cpus().length;

    // Create a worker for each CPU
    for (var i = 0; i < cpuCount; i += 1) {
        cluster.fork();
    }

    // Listen for dying workers
    cluster.on('exit', function (worker) {

        // Replace the dead worker, we're not sentimental
        console.log('Worker %d died :(', worker.id);
        cluster.fork();

    });

// Code to run if we're in a worker process
} else {

    // Include Express
    var express = require('express');

    // Create a new Express application
    var app = express();

    // Add a basic route – index page
    app.get('/', function (request, response) {
        console.log('Request to worker %d', cluster.worker.id);
        response.send('Hello from Worker ' + cluster.worker.id);
    });

    // Bind to a port
    app.listen(3000);
    console.log('Worker %d running!', cluster.worker.id);
}

And this is what I have:

app.js

var createError = require('http-errors');
var express = require('express');
var path = require('path');
var cookieParser = require('cookie-parser');
var logger = require('morgan');

var indexRouter = require('./routes/index');

var app = express();
var io = app.io = require('socket.io')();

// view engine setup
app.set('views', path.join(__dirname, 'views'));
app.set('view engine', 'pug');

app.use(logger('dev'));
app.use(express.json());
app.use(express.urlencoded({ extended: false }));
app.use(cookieParser());
app.use(express.static(path.join(__dirname, 'public')));

app.use('/', indexRouter);

// catch 404 and forward to error handler
app.use(function(req, res, next) {
    next(createError(404));
});

// error handler
app.use(function(err, req, res, next) {
    // set locals, only providing error in development
    res.locals.message = err.message;
    res.locals.error = req.app.get('env') === 'development' ? err : {};

    // render the error page
    res.status(err.status || 500);
    res.render('error');
});

var players = {};
//socket io
io.on('connection', function(socket) {
    socket.on('new player', function(data) {
        var player = {
            id: socket.id,
            name: data.name,
            color: data.color
        }
        players[socket.id] = player;
        io.to(`${socket.id}`).emit('player info', player);
    });
    socket.on('chat', function(data) {
        io.emit('message', {
            player: players[data.id],
            text: data.text
        });
    });
    socket.on('disconnect', function() {
        delete players[socket.id];
    });
});
module.exports = app;

bin/www

#!/usr/bin/env node

/**
 * Module dependencies.
 */

var app = require('../app');
var debug = require('debug')('elvin:server');
var http = require('http');

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

var port = normalizePort(process.env.PORT || '80');
app.set('port', port);

/**
 * Create HTTP server.
 */

var server = http.createServer(app);
var io = app.io
io.attach(server);

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

server.listen(port, function(){
  console.log('server listening on port ' + server.address().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);
}

What do I do? The module.exports = app; is what it is causing me troubles

Answer 1

I use my own boiler plate. I used socket, cluster and express together in it. Here is a link to it.

Desktop-CHAT-app

You can download it and make the changes over here and proceed. I've used many useful packages too.

Hope it helps!