Node.js – How to be using? Socket.io rooms or Redis pub-sub

node.jspublish-subscriberedissocket.io

Pretty simple question. I am building a realtime game using nodejs as my backend and I am wondering if there is any information available on which one is more reliable and which one is more efficient?
I am heavily using both Redis and Socket.io throughout my code. So I want to know whether I should be utilizing Socket.io's Rooms or I would be better off using redis' pub-sub ?

Update:
Just realized there is a very important reason why you may want to use redis pub/sub over socket.io rooms. With Socket.io rooms when you publish to listeners, the (browser)clients recieve the message, with redis it is actually the (redis~on server)clients who recieve messages. For this reason, if you want to inform all (server)clients of information specific to each client and maybe do some processing before passing on to browser clients, you are better off using redis. Using redis you can just fire off an event to generate each users individual data, where as with socket.io you have to actually generate all the users unique data at once, then loop through them and send them their individual data, which almost defeats the purpose of rooms, at least for me.

Unfortunately for my purposes I am stuck with redis for now.

Update 2: Ended up developing a plugin to use only 2 redis connections but still allow for individual client processing, see answer below….

Best Answer

Redis pub/sub is great in case all clients have direct access to redis. If you have multiple node servers, one can push a message to the others.

But if you also have clients in the browser, you need something else to push data from a server to a client, and in this case, socket.io is great.

Now, if you use socket.io with the Redis store, socket.io will use Redis pub/sub under the hood to propagate messages between servers, and servers will propagate messages to clients.

So using socket.io rooms with socket.io configured with the Redis store is probably the simplest for you.

Related Solutions

Node.js – How to reuse redis connection in socket.io

Actually you are only creating a new redis client for every connection if you are instantiating the client on the "connection" event. What I prefer to do when creating a chat system is to create three redis clients. One for publishing, subscribing, and one for storing values into redis.

for example:

var socketio = require("socket.io")
var redis = require("redis")

// redis clients
var store = redis.createClient()
var pub = redis.createClient()
var sub = redis.createClient()

// ... application paths go here

var socket = socketio.listen(app)

sub.subscribe("chat")

socket.on("connection", function(client){
  client.send("welcome!")

  client.on("message", function(text){
    store.incr("messageNextId", function(e, id){
      store.hmset("messages:" + id, { uid: client.sessionId, text: text }, function(e, r){
        pub.publish("chat", "messages:" + id)
      })
    })
  })

  client.on("disconnect", function(){
    client.broadcast(client.sessionId + " disconnected")
  })

  sub.on("message", function(pattern, key){
    store.hgetall(key, function(e, obj){
      client.send(obj.uid + ": " + obj.text)
    })
  })

})

Javascript – Pub/sub implementation in nodeJS

For object persistence, I added Redis support using node_redis. Then I replaced the client.send loop on the array of channels with Redis pub/sub as a layer of abstraction. But I noticed that I needed to create a new Redis client for each user that made a subscription. And I still needed to store socket.io client information to send messages to on publish. How scalable is that? Are there other (better) implementations or further optimizations I could make? What would you do?

Yes, you have to create a new redis client for every io request. It is heavy and not scalable. But creating a new redis client connection does not consume much memory. So if your system user count is not more than 5000 then it is ok. To scale you can add in slave redis server to resolve the heavy publish and subscribe and if you are concerned about creating a lot of connections then you can increase your OS uLIMIT.

You don't need to store socket.io client in message sent. Once redis received subscribed channel message. It will send message to particular io client.

subscribe.on("message",function(channel,message) { 
 var msg = { message: [client.sessionId, message] }; 
 buffer.push(msg);
 if (buffer.length 15) buffer.shift(); 
 client.send(msg); > });

To subscribe multi channel. I suggest you to pre-store all user with more than one channel(You can use storage Mongodb or redis).

var store = redis.createClient();
var subscriber= redis.createClient()

store.hgetall(UID, function(e, obj){
     subscriber.subscribe(obj.ChannelArray.toArray());
 })

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