Maximum amount of connections to a single VM

Hi!

I’m running a service on Fly where each user opens a WebSocket connection to our backend.

I’ve set my app’s concurrency settings to a hard_limit of 25k and soft_limit of 20k, but looking at Grafana it seems like each machine is only getting ~10k connections:

The machines are sitting at ~60% CPU usage and ~50% RAM, and I’d like to allow for more connections to each.

Is there some hidden limit I’m hitting here?

Hi… Are these Machines all in the same region?

The Fly Proxy considers proximity as well as connection count:

https://fly.io/docs/reference/fly-proxy-autostop-autostart/

Yes, they’re all in the same region

Hm… As a few quick pointers, to previous, similar discussions that came to mind… There were reports earlier of the Grafana App Concurrency stats not actually matching the Machine’s own internal count of active WebSockets:

And the following general caveat was mentioned elsewhere:

(That second one was written in the context of type = "requests", but the overall comment and thread is food for thought.)

It’s not a solution, per se, but hope these still help a little!


Aside: You might also want to check ulimit -H -n (the hard limit on the number of open file descriptors).

$ fly ssh console -C 'bash -c "ulimit -H -n"'
10240

This is an OS-level limit (i.e., Linux’s doing).

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