Working with WebSockets and NodeJs clusters

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I currently have a Node server running that works with MongoDB. It handles some HTTP requests, but it largely used WebSockets. Basically, the server connects multiple users to rooms with WebSockets.

My server currently has around 12k WebSockets open and it's almost crippling my single threaded server, and now I'm not sure how to convert it over.

The server holds HashMap variables for the connected users and rooms. When a user does an action, the server often references those HashMap variables. So, I'm not sure how to use clusters in this. I thought maybe creating a thread for every WebSocket message, but I'm not sure if this is the right approach, and it would not be able to access the HashMaps for the other users

Does anyone have any ideas on what to do?

Thank you.

node.js multithreading websocket performance
1 Answers

You can look at the socket.io-redis adapter for architectural ideas or you can just decide to use socket.io and the Redis adapter.

They move the equivalent of your hashmap to a separate process redis in-memory database so all clustered processes can get access to it.

The socket.io-redis adapter also supports higher-level functions so that you can emit to every socket in a room with one call and the adapter finds where everyone in the room is connected, contacts that specific cluster server, and has it send the message to them.

I thought maybe creating a thread for every WebSocket message, but I'm not sure if this is the right approach, and it would not be able to access the HashMaps for the other users

Threads in node.js are not lightweight things (each has its own V8 instance) so you will not want a nodejs thread for every WebSocket connection. You could group a certain number of WebSocket connections on a web worker, but at that point, it is likely easier to use clustering because nodejs will handle the distribution across the clusters for you automatically whereas you'll have to do that yourself for your own web worker pool.

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