create linux service with systemd inside docker container - linux

Question

Created flask application and deploying on gunicorn server on docker.
I want to write shell script to create linux service inside docker container, so I can start, stop and restart my flask app inside container.
Dockerfile:
FROM python
COPY ./app /app
WORKDIR /app
RUN pip install -r requirements.txt
EXPOSE 9003
CMD ["gunicorn", "-b", "0.0.0.0:9003", "main:app"]
Build it and run using command : docker run -p 9003:9003 myapp.
What I have tried opened docker container cli: docker exec -it <container_id> bash . You can find container id by command docker ps.
Step 1: changed directory to /etc/init.d and created myservice.service file.
[Unit]
Description=Gunicorn instance to serve app
[Service]
WorkingDirectory=/home/app
ExecStart=gunicorn --workers 3 --bind 0.0.0.0:9003 unix:app.sock -m 007 main:app
Restart=always
[Install]
WantedBy=multi-user.target
step 3: I enable service by first running cd /etc/rc3.d and then run ln -s ../init.d/{SERVICENAME} S95{SERVICENAME}
step 4: Give permission : chmod +x /etc/init.d/{SERVICENAME}
step 5: start service : `service myservice start
But this give me error
enter image description here
Docker container OS: Debian 10
Why its giving me Unit not found? any idea? How to resolve?

Answer 1

Why its giving me Unit not found? any idea? How to resolve?
You are improperly creating the file in wrong directory and creating unrelated links. You seem to be mixing rc-scripts with systemd. They are not alike, they are completely different. Toss aside rc-scripts and forget /etc/rc.d ever existed. Re-read and follow a good tutorial on how to add a systemd service file to your system.
want to write shell script to create linux service inside docker container
This will make no difference, as the container you are running does not run systemd - you run only CMD ["gunicorn"..., so your service will never be running. Typically in docker, multiple services are run with a shell script or in more complicated cases with a supervisord. In your case, there is no need to setup anything - just let the docker run the service as its pid 0 process, it's only one process. Re-research how docker works and research how services are written in docker.
What you may want to create is a service file on host, not inside docker container.

Answer 2

Thanks for answer.
Using Window 10
please see references and way what I was doing.
Created myproject.service in /etc/systemd/system inside docker container.
[Unit]
Description=Gunicorn instance to serve myproject
After=network.target
[Service]
User=sammy
Group=www-data
WorkingDirectory=/home/sammy/myproject
Environment="PATH=/home/sammy/myproject/myprojectenv/bin"
ExecStart=/home/sammy/myproject/myprojectenv/bin/gunicorn --workers 3 --bind unix:myproject.sock -m 007 wsgi:app
this newly created service is not catched and when I try to start this service using command service myproject start, It gives error unrecognized service: myproject.
How will OS know that new service has been created and to reload it.
In Linux, by running daemon-reload, It catches all new created services. But In case of docker, how to do this?
Reference: https://www.digitalocean.com/community/tutorials/how-to-serve-flask-applications-with-gunicorn-and-nginx-on-ubuntu-18-04
For rc script, Reference: https://unix.stackexchange.com/questions/106656/how-do-services-in-debian-work-and-how-can-i-manage-them