Setting up websockets in a multi-instance node environment using PM2

Question

My current setup is running multiple node instances using PM2 to manage the instances and act as a load balancer.

I would like to implement some functionality using websockets. The first issue that came to mind is sharing the sockets among X node instances.

My understanding is that if I boot up a websocket-server within a node env only that env will have access to the sockets connected to it. I do not want to load up web sockets for each instance for each user as that seems like a waste of resources.

Currently I am playing around with the websocket package on npm but I am in no way tied to this if there is a better alternative.

I would like the sockets to more or less push data one-way from server to client and avoid anything coming from the client to the server.

My solution so far is spin up another node instance that solely acts as a websocket server.

This would allow a user to make all requests as normal to the usual instances but make a websocket connection to the separate node instance dedicated to sockets.

The servee could then fire off messages to the dedicated socket server anytime something is updated to send data back to the appropriate clients.

I am not sure this is the best option and I am trying to see if there are other recommended ways of managing websockets across multiple node instances yet still allow me to spin up/down node instances as required.

Answer 1

I'd recommend you avoid a complex setup and just get socket.io working across multiple nodes, thus distributing the load; If you want to avoid data coming from the client to the server, just don't listen to incoming events on your server.

Socket.io supports multiple nodes, under the following conditions:

• You have sticky sessions enabled. This ensures requests connect back to the process from which they originated from.

• You use a special adapter called socket.io-redis & a small Redis instance as a central point of storage - it keeps track of namespaces/rooms and connected sockets across your cluster of nodes.

Here's an example:

// setup io as usual
const io = require('socket.io')(3000)

// Set a redisAdapter as an adapter.
const redisAdapter = require('socket.io-redis')
io.adapter(redisAdapter({ host: 'localhost', port: 6379 }))

From then on, it's business as usual:

io.emit('hello', 'to all clients')

You can read more here: Socket.IO - Using Multiple Nodes.