Prerequisites

• Realtime Chat With Users & Rooms - Socket.io, Node & Express
• REPO - bradtraversy/chatcord

Additional helpful resources

• Scaling Websockets with Redis, HAProxy and Node JS - High-availability Group Chat Application
• Load Balancing NodeJS applications using NginX
• Socket.IO Docs - Using multiple nodes
• Socket.IO Docs - Adapters
• Socket.IO Docs - Redis adapter

Additional Tools

• nginx
• Redis
• Node.js v14+
• http-server

Here is a MSI installer I found for Redis.

Setup

1. Clone repository
2. cd into server and npm install

Nginx conf

http {

    upstream backend {
        hash '$remote_addr $cookie_zzz $http_user_agent';
	server 127.0.0.1:1212;
        server 127.0.0.1:1213;
    }
		
    server {
        listen 80;
	root E:\\socket\\server;

	location / {
            proxy_pass http://backend;
        }
    }
}

events { }

https://stackoverflow.com/questions/59124543/nginx-not-loadbalancing-in-case-of-ip-hash

Running client

1. cd intoclient
2. run http-server . --cors --port=5500

Running server

1. cd into server and open 2 terminals for the same directory
2. Set 2 different ports ( ex: export PORT=1212 in one terminal and export PORT=1213 in the other)
3. Start nginx with the given configuration
4. npm start the server on both terminals

Now Server 1 will be started on PORT=1212 and Server 2 on PORT=1213 and the Client on PORT=5500. Two servers will be load balanced using nginx on PORT=80 so the client will be directed to either Server 1 or 2 when it hits Port 80. Hash based load balancing is enabled (to achieve stickiness) since nginx open source doesn't allow cookie based load balancing. Go to http://127.0.0.1:5500/ with 2 browsers (Edge and Chrome for example) then the 2 instances will be connected to Server 1 and 2 respectively.
Redis will act as a PubSub mechanism and is enabled using Socket.IO Redis Adapter.
NOTE: Redis adapter will not store anything, it will only do PubSub.
If you want you can store data in Redis as well.