systemd service not works in docker - docker

Question

my environment is under docker image(ubuntu 20.04), and i want to use systemd to start my service after every time i start mydocker, i have my own .service file here:
/etc/systemd/system/my.service:
[Unit]
Description=my test
Documentation=man:test auto(8) man:test_config(5)
[Service]
ExecStart=/root/test.sh
Type=oneshot
[Install]
WantedBy=multi-user.target
/root/test.sh have been chmod 777:
#!/bin/bash
echo "hello~" > /usr/local/test.log
exit 0
and I did follows operation:
systemctl enable my.service
docker stop mydocker
docker start mydocker
docker exec -it mydocker bash
but after I start mydocker, I didn't see /root/test.sh executed, and i check service status like this:
my.service - my test auto
Loaded: loaded (/etc/systemd/system/my.service, enabled)
Active: inactive (dead)
manually trigger service is okay:
root#:/# systemctl start my.service
root#:/# cat /usr/local/test.log
hello~
did I omit something? or systemd could not work well in docker?
thanks.

Answer 1

suggestion #1
Docker images are expected to run an initial command/program specified in the docker image generation dockerfile properties:
ENTRYPOINT
CMD
See here: https://blog.knoldus.com/a-look-at-cmd-and-entrypoint-in-dockerfile/
suggestion #2
In your /etc/systemd/system/my.service: [unit] section add Requires=Network.target and After=Network.target:
Like this:
[Unit]
Description=my test
Documentation=man:test auto(8) man:test_config(5)
Requires=Network.target
After=Network.target
[Service]
ExecStart=/root/test.sh
Type=oneshot
[Install]
WantedBy=multi-user.target
suggestion #3
Do not use systemd services in docker image.
Use crontab job at boot time.
https://www.linode.com/docs/guides/run-jobs-or-scripts-using-crontab-on-boot/
crontab job
#boot /root/test.sh