WebSocket is to manage the connections to a browser from an app on server
Chat application with just WebSocket does not scale as the connection between Browser and Server is stateful, and we want to add more server to handle increasing traffic ⇒ We need a way to make server communicate with each other to deliver message from user connected to different server
Solution: PubSub Architecture (Redis is a popular choice)
Here we have a Load Balancer in the middle to manage/route traffic to different server
There will be a 2 part websocket connection between Brower — Load Balancer — Server
The server will listen for websocket message, and for each new message the server will publish to Redis (utilizing PubSub feature of Redis)
Everytime Redis receives new message, it will again push them to every subscribed server
E.g:
Client1, Client2, Client3 in the same group chat
Client1 connect to Server1
Client2 connect to Server2
Client3 connect to Server3
Client1 send new message and it is routed to Server1
Server published message to Redis
Redis receives message and push to all subscriber of the current topic/room/group which is Server2 and Server3
Server2 and Server3 receive new message and populate back to Client2 and Client3
