Websocket (node.js) connection limit, clients are getting disconnected after reaching 400-450 connections

Question

I have a big problem with socket.io connection limit. If the number of connections is more than 400-450 connected clients (by browsers) users are getting disconnected. I increased soft and hard limits for tcp but it didn't help me. The problem is only for browsers. When I tried to connect by socket-io-client module from other node.js server I reached 5000 connected clients. Its very big problem for me and totally blocked me. Please help.

Update

I have tried with standard Websocket library (ws module with node.js) and problem was similar. I can reach only 456 connected clients.

Update 2

I devided connected clients between a few instances of server. Every group of clients were connecting by other port. Unfortunately this change didn't help me. Sum of connected users was the same like before.

Solved (2018)

There were not enough open ports for a Linux user which run the pm2 manager ("pm2" or "pm" username).

Answer 1

You may be hitting a limit in your operating system. There are security limits in the number of concurrent files open, take a look at this thread.

https://github.com/socketio/socket.io/issues/1393

Update: I wanted to expand this answer because I was answering from mobile before. Each new connection that gets established is going to open a new file descriptor under your node process. Of course, each connection is going to use some portion of RAM. You would most likely run into the FD limit first before running out of RAM (but that depends on your server).

Check your FD limits: https://rtcamp.com/tutorials/linux/increase-open-files-limit/

And lastly, I suspect your single client concurrency was not using the correct flags to force new connections. If you want to test concurrent connections from one client, you need to set a flag on the webserver:

var socket = io.connect('http://localhost:3000', {'force new connection': true});