Websockets in Node.js - Making them reliable and scalable
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This document discusses implementing websockets in Node.js. It covers popular websocket libraries like Socket.io and Engine.io, considerations for reliability and scalability, and using Redis for pub/sub to allow messages to be passed between servers and achieve scalable websockets. Code examples are provided for setting up websockets on both the client and server sides using Engine.io and Redis.
![LISTENING ON THE SERVER
socket.on('connection', function (client) {
client.send('123456');
client.on('message', function (data) {
for (var key in socket.clients ) {
if(typeof client.id !== 'undefined') {
if(key == client.id) {
continue;
}
}
socket.clients[key].send(data);
}
});
});](https://image.slidesharecdn.com/websockets-131119220434-phpapp02/85/Websockets-in-Node-js-Making-them-reliable-and-scalable-8-320.jpg)
![RECEIVING A MESSAGE FROM REDIS
var sub = redis.createClient();
sub.on('ready', function() {
sub.subscribe('subscription-channel');
sub.on('message', function(channel, message) {
for( var key in socket.clients ) {
socket.clients[key].send(message);
}
});
});](https://image.slidesharecdn.com/websockets-131119220434-phpapp02/85/Websockets-in-Node-js-Making-them-reliable-and-scalable-17-320.jpg)
Websockets in Node.js - Making them reliable and scalable
- 3. WHAT SHOULD WE CONSIDER? • • • RELIABILITY SCALABILITY HOSTING
- 4. HOW CAN WE IMPLEMENT THEM? • • • SOCKET.IO – MOST POPULAR BUT LEAST RELIABLE SOCKJS – A REASONABLE ALTERNATIVE ENGINE.IO – RELIABLE BUT LOW LEVEL
- 5. EXAMPLE – IMPLEMENTING IN ENGINE.IO
- 6. SETTING THE CONNECTION ON THE CLIENT function connectSocket() { socket = eio("http://localhost:8080/"); socket.onopen = function() { socket.onmessage = function(package) { // Handling received messages }; }; socket.onclose = function() { console.log("Disconnected from websocket"); connectionAttempts++; if (connectionAttempts < 10) { connectSockets(); } } }
- 7. SENDING AN OBJECT FROM THE CLIENT var newMessage = { owner: ‚Gareth‛, message: ‚Hello there‛ } var action = ‚greetings‛; sendMessage(action, data); function sendMessage(action, data) { var socketPackage = { action: action, data: data } this.socket.send(JSON.stringify(socketPackage)); }
- 8. LISTENING ON THE SERVER socket.on('connection', function (client) { client.send('123456'); client.on('message', function (data) { for (var key in socket.clients ) { if(typeof client.id !== 'undefined') { if(key == client.id) { continue; } } socket.clients[key].send(data); } }); });
- 9. REMEMBER TO ALLOW CROSS DOMAINS IN EXPRESS! var app = express(); app.configure(function() { app.use(function(req, res, next) { res.header("Access-Control-Allow-Origin", "*"); res.header("Access-Control-Allow-Headers", "X-Requested-With"); next(); }); });
- 10. RECEIVING AN OBJECT ON THE CLIENT function connectSockets() { socket = eio(‘http://localhost:8080/’); socket.onopen = function() { socket.onmessage = function(package) { var socketPackage = JSON.parse(package.data); if (socketPackage.action != null) { switch(socketPackage.action) { case ‘greetings’: console.log(socketPackage.data.message); break; } } }; }; }
- 12. PROBLEMS WITH SCALING • • WEBSOCKETS REQUIRE “STICKY SESSIONS” WEBSOCKETS ONLY EXIST ON THE SERVER THE CLIENT CONNECTED TO
- 13. CLIENTS CAN’T PASS MESSAGES BETWEEN SERVERS!
- 14. REDIS TO THE RESCUE! • • REDIS HAS A PUB/SUB QUEUE HAVE ALL OUR SERVER INSTANCES PUBLISHING AND SUBSCRIBING TO THE QUEUE • PASS MESSAGES BETWEEN SERVERS USING THE QUEUE
- 15. PASSING MESSAGES WITH REDIS
- 16. PUBLISH A RECEIVED MESSAGE THROUGH REDIS var pub = redis.createClient(); socket.on('connection', function (client) { client.send('123456'); client.on('message', function (data) { try { pub.publish('subscription-channel', data); } catch (err) { console.log("Error publishing: " + err); } }); });
- 17. RECEIVING A MESSAGE FROM REDIS var sub = redis.createClient(); sub.on('ready', function() { sub.subscribe('subscription-channel'); sub.on('message', function(channel, message) { for( var key in socket.clients ) { socket.clients[key].send(message); } }); });
- 19. THANK YOU!