How to balance the load with NGINX and multiple servers

[El-Tommy]

I have a server running with PM2, which lets me use all the machine’s vCPUs (02) to get better Socket.IO performance. This server has 4GB of RAM.

Since I’m using PM2, I have an NginX server in front that receives HTTPS/WSS requests and forwards them to port 8080.

I use the configuration below to allow the nodes to communicate correctly, as per the instructions on the website.

const http = require("http");
const { Server } = require("socket.io");
const { createAdapter } = require("@socket.io/cluster-adapter");
const { setupWorker } = require("@socket.io/sticky");

const infoServer = {
    success: true,
}

const httpServer = http.createServer((req, res) => {
    res.writeHead(200, { "Content-Type": "application/json" });
    res.write(JSON.stringify(infoServer));
    res.end();
});

const io = new Server(httpServer, {
    cors: {
        origin: "*",
        methods: ["GET", "POST"]
    }
});

io.adapter(createAdapter());
setupWorker(io);

However, in my current scenario, it hasn’t been a good solution, especially for scalability.
If an issue occurs on the server—such as exhausting all RAM or hitting a file limit (tuning has already been done)—the entire service goes offline, so I’m thinking of using another machine, also with 2 vCPUs, to load-balance and provide high availability.

The scenario would be:

Nginx server:
-> Socket.IO Server 01 + 2 vCPUs running
-> Socket.IO Server 02 + 2 vCPUs running

But my question is what I need to change in my code for this to work.
From what I understand, in NginX I need to add the code below.

upstream nodes {
    # enable sticky session with either "hash" (uses the complete IP address)
    hash $remote_addr consistent;
    # or "ip_hash" (uses the first three octets of the client IPv4 address, or the entire IPv6 address)
    # ip_hash;
    # or "sticky" (needs commercial subscription)
    # sticky cookie srv_id expires=1h domain=.example.com path=/;

    server app01:8080;
    server app02:8080;
    server app03:8080;
  }

https://socket.io/docs/v4/using-multiple-nodes/#nginx-configuration

I really didn’t understand this part. If I’m going to use multiple servers, do I have to use only one CPU? Or can I keep using all the CPUs available on the machines?

Should I remove Socket.IO’s sticky mechanism?

Is that it? Could someone give me more details?