We had massive issues running Elixir in a container until we tweaked the vm settings. This is in our vm.args.eex

## Enable kernel poll
+K true

## Aysnc threads
+A 128

## Increase number of concurrent ports/sockets
## Same as setting: -env ERL_MAX_PORTS 65536
+Q 65536

## Something about scheduling
## https://stressgrid.com/blog/beam_cpu_usage/
+sbwt none
+sbwtdcpu none
+sbwtdio none

For anyone coming to this thread in future here’s some of what @garazdawi said in the thread on EFS:

See his full response and the rest of the thread here:

We were seeing our Elixir/Phoenix servers crash after ~1000 simultaneous connections.
Also, we had to change the tcp_keepalive_time and file-max

sysctl -w net.ipv4.tcp_keepalive_time=250 fs.file-max=1024000

It looks like +K was removed into OTP 21 and +A may have less impact now with the introduction of the dirty scheduler. +Q appears to default to 65536 so maybe that’s not needed anymore?

It would be wonderful if the vm settings I used weren’t needed anymore – it was miserable and confusing. Also, there was very little written about it, so there was a bunch of guessing and hoping on my part.

+sbwt none
+sbwtdcpu none
+sbwtdio none

I think the import parts were these one above. Do you know much about those settings, @mattbaker? I’d love to know what I was changing – at the time, it felt like reciting a magical incantation.

We’ve had an easy time running in containers but I want to call out the sbwt options in particular, they significantly dropped our CPU usage (at least as CFS was measuring it)

I’m so curious about these other options @scottmessinger, if you ever write something up about what led you to them I’d love to read it

These are the options I’m using as of last night;

   +c true 
   +C multi_time_warp
   +sub true
   +swt very_low
   +swtdio very_low
   +sbwt none
   +sbwtdcpu none
   +sbwtdio none