Socket.io - using multiple nodes

So I was looking into running socket.io across multiple processes.

The guide here: https://socket.io/docs/using-multiple-nodes/ left me with some questions.

It mentions using configuring nginx to load balance between socket.io processes, but it also mentions using the built in cluster module in Node.js below.

Am I supposed to be using nginx AND the cluster module in Node.js for this?

Also how do I tell if load balancing is working?

I tested it using the nginx option with two socket.io processes running using the redis adapter and using the cluster module.

This is what I had in my nginx config:

http {

        upstream io_nodes {
        ip_hash;
        server 127.0.0.1:6001;
        server 127.0.0.1:6002;
        }

        server {
        listen 3000;
        server_name example.com;
        location / {
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection "upgrade";
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header Host $host;
        proxy_http_version 1.1;
        proxy_pass http://io_nodes;
        }
        }

This is an example of my socket.io code (most of it taken from here: https://github.com/elad/node-cluster-socket.io):

var express = require('express'),
    cluster = require('cluster'),
    net = require('net'),
    redis = require('redis'),
    sio = require('socket.io'),
    sio_redis = require('socket.io-redis');

var port = 6001,
    num_processes = require('os').cpus().length;

if (cluster.isMaster) {
    console.log('is master 6001');
    // This stores our workers. We need to keep them to be able to reference
    // them based on source IP address. It's also useful for auto-restart,
    // for example.
    var workers = [];

    // Helper function for spawning worker at index 'i'.
    var spawn = function(i) {
        workers[i] = cluster.fork();

        // Optional: Restart worker on exit
        workers[i].on('exit', function(code, signal) {
            console.log('respawning worker', i);
            spawn(i);
        });
    };

    // Spawn workers.
    for (var i = 0; i < num_processes; i++) {
        spawn(i);
    }

    // Helper function for getting a worker index based on IP address.
    // This is a hot path so it should be really fast. The way it works
    // is by converting the IP address to a number by removing non numeric
  // characters, then compressing it to the number of slots we have.
    //
    // Compared against "real" hashing (from the sticky-session code) and
    // "real" IP number conversion, this function is on par in terms of
    // worker index distribution only much faster.
    var worker_index = function(ip, len) {
        var s = '';
        for (var i = 0, _len = ip.length; i < _len; i++) {
            if (!isNaN(ip[i])) {
                s += ip[i];
            }
        }

        return Number(s) % len;
    };

    // Create the outside facing server listening on our port.
    var server = net.createServer({ pauseOnConnect: true }, function(connection) {
        // We received a connection and need to pass it to the appropriate
        // worker. Get the worker for this connection's source IP and pass
        // it the connection.
        var worker = workers[worker_index(connection.remoteAddress, num_processes)];
        worker.send('sticky-session:connection', connection);
    }).listen(port);
} else {
    // Note we don't use a port here because the master listens on it for us.
    var app = new express();

    // Here you might use middleware, attach routes, etc.

    // Don't expose our internal server to the outside.
    var server = app.listen(0, 'localhost'),
        io = sio(server);

    // Tell Socket.IO to use the redis adapter. By default, the redis
    // server is assumed to be on localhost:6379. You don't have to
    // specify them explicitly unless you want to change them.
    io.adapter(sio_redis({ host: 'localhost', port: 6379 }));

    // Here you might use Socket.IO middleware for authorization etc.
        io.on('connection', function(socket) {
        console.log('port 6001');
        console.log(socket.id);
    });
    // Listen to messages sent from the master. Ignore everything else.
    process.on('message', function(message, connection) {
        if (message !== 'sticky-session:connection') {
            return;
        }
        // Emulate a connection event on the server by emitting the
        // event with the connection the master sent us.
        server.emit('connection', connection);

        connection.resume();
    });
}

Connections worked just fine with this, although I'm testing it all locally..

How do I know if it's working properly? Every time the client connects, it seems to connect to the socket.io process on port 6001.

The client connect code connects to port 3000.