Erlang: rebar3 release, start beam first? - docker

Question

I am trying to utilize a new feature in 19.3 per this question: Erlang: does the application behavior trap SIGTERM?
My understanding is that sending SIGTERM to BEAM now triggers a graceful shutdown in Erlang 19.3+
I start my application in Docker using the ENTRYPOINT ./_build/default/rel/myapp/bin/myapp where ./_build/default/rel/myapp/bin/myapp is generated from rebar3 release
When I do this in Docker, myapp gets PID1 and BEAM seems to gets another PID.
Is there a different set of commands I can run such that BEAM gets PID1 and myapp gets loaded from there? Something like
./start_beam; ./start_my_app_via_beam?
I need this because docker stop sends SIGTERM to the PID1. I need that to be BEAM. Using the above entrypoint, here is what happens in the container":
top
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
1 root 20 0 4340 644 556 S 0.0 0.0 0:00.01 myapp
14 root 20 0 3751188 50812 6660 S 0.0 0.6 0:00.48 beam.smp
18 root 20 0 11492 116 0 S 0.0 0.0 0:00.00 epmd
31 root 20 0 4220 680 604 S 0.0 0.0 0:00.10 erl_child_setup
53 root 20 0 11456 944 840 S 0.0 0.0 0:00.00 inet_gethost
54 root 20 0 17764 1660 1504 S 0.0 0.0 0:00.00 inet_gethost
55 root 20 0 20252 3208 2720 S 0.0 0.0 0:00.02 bash
61 root 20 0 21956 2468 2052 R 0.0 0.0 0:00.00 top

Answer 1

Currently, to get around this, I have this horrendous beast:
#!/usr/bin/env bash
echo "if testing locally send SIGTERM to $$"
term_handler() {
echo "Stopping the Erlang VM gracefully"
#/usr/local/Cellar/erlang/19.1/lib/erlang/lib/erl_interface-
3.9.1/bin/erl_call -c myapp -s -a 'init stop' -n 'myapp#localhost'
/usr/local/lib/erlang/lib/erl_interface-3.9.2/bin/erl_call -c myapp -s -a 'init stop' -n 'myapp#localhost'
echo "Erlang VM Stopped"
}
trap term_handler SIGQUIT SIGINT SIGTERM
./_build/default/rel/myapp/bin/myapp &
PID=$!
echo "Erlang VM Started"
#wait $PID
while kill -0 $PID ; do wait $PID ; EXIT_STATUS=$? ; done
echo "Exiting Wrapper."
exit $EXIT_STATUS
```
And then I do `ENTRYPOINT : ["./thisscript"]`
This beast becomes PID 1, and it finds the correct thing to kill after that.
I'm trying to get rid of this script.