docker-compose command is unable to stop gracefully - docker

Question

My custom docker-compose command won't stop gracefully. Why isn't the below working and how can I fix it properly (i.e. no SIGKILL)?
This is mentioned in the docs: https://docs.docker.com/compose/faq
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I've written these tests to demonstrate:
version: '3.3'
services:
# My personal use case
test1_string:
image: python:3.9.0rc1-alpine3.12
command: 'python -u -m smtpd -n -c DebuggingServer 0.0.0.0:1025'
# https://docs.docker.com/compose/faq/
# "Compose always uses the JSON form, so don’t worry if you override the command or entrypoint in your Compose file."
test2_list:
image: python:3.9.0rc1-alpine3.12
command: ['python', '-u', '-m', 'smtpd', '-n', '-c', 'DebuggingServer', '0.0.0.0:1025']
# Maybe it's an issue with networking and syscalls?
# Using nc once for a comparison to smtpd DebuggingServer above
test3_bash:
image: bash:5.0.18
command: ['bash', '-c', 'nc -k -l 4444 > filename.out']
# Something simpler, just a sleep.
test4_bash_sleep:
image: bash:5.0.18
command: ['bash', '-c', 'sleep 100']
# Apparently bash doesn't forward signals, but exec can help (?)
test5_bash_exec:
image: bash:5.0.18
command: ['bash', '-c', 'exec sleep 100']
# Print any signals sent to the executable
test6_bash_trap:
image: bash:5.0.18
command: ['bash', '-c', 'for s in HUP INT TERM KILL EXIT ; do trap "echo $$s; exit 0" $$s ; done ; sleep 100']
# Finally, use SIGKILL instead of SIGTERM. This works, but is overkill and not at all graceful.
test7_kill:
image: python:3.9.0rc1-alpine3.12
command: ['python', '-u', '-m', 'smtpd', '-n', '-c', 'DebuggingServer', '0.0.0.0:1025']
stop_signal: SIGKILL
This is the output, hitting Ctrl-C after theyre up:
$ docker-compose --version
docker-compose version 1.25.4, build unknown
$ docker --version
Docker version 19.03.11, build 42e35e6
$ docker-compose up
Creating docker_stop_test2_list_1 ... done
Creating docker_stop_test1_string_1 ... done
Creating docker_stop_test6_bash_trap_1 ... done
Creating docker_stop_test4_bash_sleep_1 ... done
Creating docker_stop_test7_kill_1 ... done
Creating docker_stop_test5_bash_exec_1 ... done
Creating docker_stop_test3_bash_1 ... done
Attaching to docker_stop_test4_bash_sleep_1, docker_stop_test5_bash_exec_1, docker_stop_test2_list_1, docker_stop_test3_bash_1, docker_stop_test6_bash_trap_1, docker_stop_test7_kill_1, docker_stop_test1_string_1
^CGracefully stopping... (press Ctrl+C again to force)
Stopping docker_stop_test5_bash_exec_1 ...
Stopping docker_stop_test3_bash_1 ...
Stopping docker_stop_test6_bash_trap_1 ...
Stopping docker_stop_test7_kill_1 ... done
Stopping docker_stop_test1_string_1 ...
Stopping docker_stop_test2_list_1 ...
Stopping docker_stop_test4_bash_sleep_1 ...
test7_kill is the only one that stops but it's using SIGKILL. How can I make any of the others work?