Skip to main content

CLUSTERING WEB SOCKETS WITH SOCKET.IO AND EXPRESS 3

Node.js gets a lot of well-deserved press for its impressive performance. The event loop can handle pretty impressive loads with a single process. However, most servers have multiple processors, and I, for one, would like to take advantage of them. Node’s cluster api can help.
While cluster is a core api in node.js, I’d like to incorporate it with Express 3 and Socket.io.
Final source code available on github
The node cluster docs gives us the following example.
1
2
3
4
5
6
7
8
9
10
11
12
cluster = require("cluster")
http = require("http")
numCPUs = require("os").cpus().length
if cluster.isMaster
  i = 0
  while i < numCPUs     cluster.fork()     i++   cluster.on "exit", (worker, code, signal) ->
    console.log "worker " + worker.process.pid + " died"
else
  http.createServer((req, res) ->
    res.writeHead 200
    res.end "hello world\n"
  ).listen 8000
The code compiles and runs, but I have not confirmation that things are actually working. I’d like to add a little logging to confirm that we actually have multiple workers going. Lets add these lines right before the ‘exit’ listener.
1
2
cluster.on 'fork', (worker) ->
  console.log 'forked worker ' + worker.id
On my machine, we get this output:
coffee server
forked worker 1
forked worker 2
forked worker 3
forked worker 4
forked worker 5
forked worker 6
forked worker 7
forked worker 8
So far, so good. Lets add express to the mix.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
cluster = require("cluster")
http = require("http")
numCPUs = require("os").cpus().length
if cluster.isMaster
  i = 0
  while i < numCPUs     cluster.fork()     i++   cluster.on 'fork', (worker) ->
    console.log 'forked worker ' + worker.process.pid
  cluster.on "listening", (worker, address) ->
    console.log "worker " + worker.process.pid + " is now connected to " + address.address + ":" + address.port
  cluster.on "exit", (worker, code, signal) ->
    console.log "worker " + worker.process.pid + " died"
else
  app = require("express")()
  server = require("http").createServer(app)
  server.listen 8000
  app.get "/", (req, res) ->
    console.log 'request handled by worker with pid ' + process.pid
    res.writeHead 200
    res.end "hello world\n"
At this point, I’d like to throw a few http requests against the setup to ensure that I’m really utilizing all my processors.
Running (curl -XGET “http://localhost:8000&#8221;) 6 times makes the node process go:
request handled by worker with pid 85229
request handled by worker with pid 85231
request handled by worker with pid 85231
request handled by worker with pid 85231
request handled by worker with pid 85227
request handled by worker with pid 85229
Alright, last step is getting socket.io involved. Just a couple extra lines for the socket, however, we’ll need to add a basic index.html file to actually make the socket calls.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
cluster = require("cluster")
http = require("http")
numCPUs = require("os").cpus().length
if cluster.isMaster
  i = 0
  while i < numCPUs     cluster.fork()     i++   cluster.on 'fork', (worker) ->
    console.log 'forked worker ' + worker.process.pid
  cluster.on "listening", (worker, address) ->
    console.log "worker " + worker.process.pid + " is now connected to " + address.address + ":" + address.port
  cluster.on "exit", (worker, code, signal) ->
    console.log "worker " + worker.process.pid + " died"
else
  app = require("express")()
  server = require("http").createServer(app)
  io = require("socket.io").listen(server)
  server.listen 8000
  app.get "/", (req, res) ->
    res.sendfile(__dirname + '/index.html');
  io.sockets.on "connection", (socket) ->
    console.log 'socket call handled by worker with pid ' + process.pid
    socket.emit "news",
      hello: "world"
1
2
3
4
5
6
7
8
9
10
11
<script class="hiddenSpellError" type="text/javascript">// <![CDATA[
src</span>="/socket.io/socket.io.js">
// ]]></script><script type="text/javascript">// <![CDATA[
// ]]></script>
 var socket = io.connect('http://localhost');
 socket.on('news', function (data) {
 console.log(data);
 socket.emit('my other event', { my: 'data' });
 });
// ]]></script>
When I run this code, problems start to appear. Specifically, the following message shows up in my output
warn – client not handshaken client should reconnect
Not surprisingly, we have issues with sockets appearing disconnected. Socket.io defaults to storing its open sockets in an in-memory store. As a result, sockets in other processes have no access to the information. We can easily fix the problem by using the redis store for socket.io. The docs we need are here.

With the redis store in place, it looks like this:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
cluster = require("cluster")
http = require("http")
numCPUs = require("os").cpus().length
RedisStore = require("socket.io/lib/stores/redis")
redis = require("socket.io/node_modules/redis")
pub = redis.createClient()
sub = redis.createClient()
client = redis.createClient()
if cluster.isMaster
  i = 0
  while i < numCPUs     cluster.fork()     i++   cluster.on 'fork', (worker) ->
    console.log 'forked worker ' + worker.process.pid
  cluster.on "listening", (worker, address) ->
    console.log "worker " + worker.process.pid + " is now connected to " + address.address + ":" + address.port
  cluster.on "exit", (worker, code, signal) ->
    console.log "worker " + worker.process.pid + " died"
else
  app = require("express")()
  server = require("http").createServer(app)
  io = require("socket.io").listen(server)
  io.set "store", new RedisStore(
    redisPub: pub
    redisSub: sub
    redisClient: client
  )
  server.listen 8000
  app.get "/", (req, res) ->
    res.sendfile(__dirname + '/index.html');
  io.sockets.on "connection", (socket) ->
    console.log 'socket call handled by worker with pid ' + process.pid
    socket.emit "news",
      hello: "world"

Comments

Post a Comment

Popular posts from this blog

4 Ways to Communicate Across Browser Tabs in Realtime

1. Local Storage Events You might have already used LocalStorage, which is accessible across Tabs within the same application origin. But do you know that it also supports events? You can use this feature to communicate across Browser Tabs, where other Tabs will receive the event once the storage is updated. For example, let’s say in one Tab, we execute the following JavaScript code. window.localStorage.setItem("loggedIn", "true"); The other Tabs which listen to the event will receive it, as shown below. window.addEventListener('storage', (event) => { if (event.storageArea != localStorage) return; if (event.key === 'loggedIn') { // Do something with event.newValue } }); 2. Broadcast Channel API The Broadcast Channel API allows communication between Tabs, Windows, Frames, Iframes, and  Web Workers . One Tab can create and post to a channel as follows. const channel = new BroadcastChannel('app-data'); channel.postMessage(data); And oth...
Post a Comment
Read more

Certbot SSL configuration in ubuntu

  Introduction Let’s Encrypt is a Certificate Authority (CA) that provides an easy way to obtain and install free  TLS/SSL certificates , thereby enabling encrypted HTTPS on web servers. It simplifies the process by providing a software client, Certbot, that attempts to automate most (if not all) of the required steps. Currently, the entire process of obtaining and installing a certificate is fully automated on both Apache and Nginx. In this tutorial, you will use Certbot to obtain a free SSL certificate for Apache on Ubuntu 18.04 and set up your certificate to renew automatically. This tutorial will use a separate Apache virtual host file instead of the default configuration file.  We recommend  creating new Apache virtual host files for each domain because it helps to avoid common mistakes and maintains the default files as a fallback configuration. Prerequisites To follow this tutorial, you will need: One Ubuntu 18.04 server set up by following this  initial ...
Post a Comment
Read more

Working with Node.js streams

  Introduction Streams are one of the major features that most Node.js applications rely on, especially when handling HTTP requests, reading/writing files, and making socket communications. Streams are very predictable since we can always expect data, error, and end events when using streams. This article will teach Node developers how to use streams to efficiently handle large amounts of data. This is a typical real-world challenge faced by Node developers when they have to deal with a large data source, and it may not be feasible to process this data all at once. This article will cover the following topics: Types of streams When to adopt Node.js streams Batching Composing streams in Node.js Transforming data with transform streams Piping streams Error handling Node.js streams Types of streams The following are four main types of streams in Node.js: Readable streams: The readable stream is responsible for reading data from a source file Writable streams: The writable stream is re...
Post a Comment
Read more