Maximum concurrent Socket.IO connections

This article may help you along the way: http://drewww.github.io/socket.io-benchmarking/

I wondered the same question, so I ended up writing a small test (using XHR-polling) to see when the connections started to fail (or fall behind). I found (in my case) that the sockets started acting up at around 1400-1800 concurrent connections.

This is a short gist I made, similar to the test I used: https://gist.github.com/jmyrland/5535279

I tried to use socket.io on AWS, I can at most keep around 600 connections stable.

And I found out it is because socket.io used long polling first and upgraded to websocket later.

after I set the config to use websocket only, I can keep around 9000 connections.

Set this config at client side:

const socket = require('socket.io-client')
const conn = socket(host, { upgrade: false, transports: ['websocket'] })

GO THROUGH THE COMMENT OF THIS ANSWER BEFORE PROCEEDING FURTHER

The question ask about socket.io sockets, the answer is for native sockets. These changes are dangerous as they apply to everything on the system, not just socket.io sockets. Besides, today networks is never the bottleneck for socket.io. Do not make these changes to your system without understanding the implications first.

For +300k concurrent connection:

Set these variables in /etc/sysctl.conf:

fs.file-max = 10000000 
fs.nr_open = 10000000

Also, change these variables in /etc/security/limits.conf:

* soft nofile 10000000
* hard nofile 10000000
root soft nofile 10000000
root hard nofile 10000000

And finally, increase TCP buffers in /etc/sysctl.conf, too:

net.ipv4.tcp_mem = 786432 1697152 1945728
net.ipv4.tcp_rmem = 4096 4096 16777216
net.ipv4.tcp_wmem = 4096 4096 16777216

for more information please refer to this.

This guy appears to have succeeded in having over 1 million concurrent connections on a single Node.js server.

http://blog.caustik.com/2012/08/19/node-js-w1m-concurrent-connections/

It's not clear to me exactly how many ports he was using though.