What is the maximum client concurrent connections that web socket server can accept?

[Kojesnik]

Hi, Me and my team trying to use your lib as a ws server. And we faced a 3727 connections limit and nothing helps.
In another issue, u mentioned that it can be thread limit, but no, I have been tested it, and server can handle a big amount of threads. What can be the problem? What could it be?

[marci4]

Hello @Kojesnik,

please provide your example application.

Best regards,
Marcel

[Kojesnik]

@marci4

I found the problem. I tried to create a separate application and test it on our server to see is it a problem with threads size / memory.
And YES! The connection limit increased from 3727 to 4078. In this issue #340 you mentioned that it can be problem with how much Threads can spawn server.
I checked all JVM and SYSTEM params, but nothing helps.

By default number of WebSocketWorkers = Runtime.getRuntime().availableProcessors(). For me it is 12.
I tried to set decodersCount = 16 and all is fine, without problems 16 WebSocketWorkers were created but 4078 conn limit still presented. So I guess it is not problem with threads

Any ideas on what can be the problem?

Best regards,
Mike

[Kojesnik]

@marci4

Figured out, that for some reason your lib creating so much open files.
netstat shows 4k websocket established connections, while lsof shows over 70k.
My test server simple as it can be, so I dont know why this heppens.
When I switched to netty, and wrote ws server on it, there is no such problem and everything works great

[NoahAndrews]

That's an interesting observation

[bhaswanth88]

Even I am facing similar situation. Any workaround/tweaks to accept higher number of connections?

[DevasiaThomas]

@marci4

Figured out, that for some reason your lib creating so much open files. netstat shows 4k websocket established connections, while lsof shows over 70k. My test server simple as it can be, so I dont know why this heppens.

Are those socket files? Maybe thats why sockets are getting extinguished and its capping at the max you mentioned

When I switched to netty, and wrote ws server on it, there is no such problem and everything works great

What framework did you switch to? Or did you just implement it yourself?

[Kojesnik]

@DevasiaThomas as I remember, I used netty

[DevasiaThomas]

@Kojesnik @bhaswanth88 This blogpost and its associated whitepaper is what got me here. It's benchmark shows that this library can go to 10k connections. The benchmarks stops there. Maybe you can try run the benchmark in your env to find the culprit?

[DevasiaThomas]

I tried running the benchmark myself upto 20k connections(200 rounds, 100 per round).. Apparently increments of 100 connections is fine, but when i tried ramping up by 1000 connections per round - it didn't progress beyond the second round 😅 .. @marci4 Maybe there is some clue in the above behavior?

Another thing that was observed was that the benchmark after 200 rounds didn't have success closing the connections. I ended up killing the client process. but the socket files (lsof) persisted in the server for 2 hours and maybe more(my machine auto restarted due to updates)