I want to put a hard limit on the max number of WS connections to max 100. I'm writing a node.js server where I should not allow more than 100 connections.
How to limit the number of Websocket connection without touching system ulimit?
1 Answer
Just to expand on a comment I added, I am able to restrict the amount of websocket connections my server opens by using the per-session ulimit -n command.
I.e., before starting my websocket server, in a console I run:
ulimit -n 12
.. which succeeds (run ulimit -a to confirm)
I then start my server and trace its system calls by prefixing the command with strace:
strace -F -f -e trace=network ./myserver --port 33345
I then make many concurrent client connections. After around 6 to 8 are connections are established, further client attempts fail, and I see this in the server strace output:
[pid 24344] accept4(10, NULL, NULL, SOCK_CLOEXEC|SOCK_NONBLOCK) = -1 EMFILE (Too many open files)
[pid 24344] accept4(10, NULL, NULL, SOCK_CLOEXEC|SOCK_NONBLOCK) = 9
[pid 24344] accept4(10, NULL, NULL, SOCK_CLOEXEC|SOCK_NONBLOCK) = -1 EAGAIN (Resource temporarily unavailable)
Note that new terminal sessions don't see this ulimit, I have not changed any server-wide settings.
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I m running some other server in some other port also. so I cant change system ulimit. That I have already specified in my question.– SomnathCommented Nov 7, 2019 at 4:09
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this is not changing the system limit, but the limits associated with a shell. So can be set for starting individual processes. More here: unix.stackexchange.com/questions/75996/… and unix.stackexchange.com/questions/55319/… Commented Nov 7, 2019 at 7:50
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Additionally, you can modify your node.js server to sets the ulimit itself, see here: stackoverflow.com/questions/8141057/… Commented Nov 7, 2019 at 7:52
ulimit -n 110