How to extend nginx docker image without getting error systemctl: command not found?

Question

I want to build my own custom docker image from nginx image.

I override the ENTRYPOINT of nginx with my own ENTERYPOINT file.

Which bring me to ask two questions:

1. I think I lose some commands from nginx by doing so. am I right? (like expose the port.. )

2. If I want to restart the nginx I run this commands: nginx -t && systemctl reload nginx. but the output is:

   nginx: configuration file /etc/nginx/nginx.conf test is successful

   /entrypoint.sh: line 5: systemctl: command not found

How to fix that?

FROM nginx:latest

WORKDIR /

RUN echo "deb http://ftp.debian.org/debian stretch-backports main" >> /etc/apt/sources.list

RUN apt-get -y update && \
    apt-get -y install apt-utils && \
    apt-get -y upgrade && \
    apt-get -y clean

# I ALSO WANT TO INSTALL CERBOT FOR LATER USE (in my entrypoint file)

RUN apt-get -y install python-certbot-nginx -t stretch-backports

# COPY ./something ./tothisimage 
# COPY ./something ./tothisimage 
# COPY ./something ./tothisimage 
# COPY ./something ./tothisimage 

COPY entrypoint.sh /entrypoint.sh

ENTRYPOINT ["bash", "/entrypoint.sh"]

entrypoint.sh

echo "in entrypoint"

# I want to run some commands here... 

# After I want to run nginx normally....

nginx -t && systemctl reload nginx

echo "after reload"

Answer 1

Commands like service and systemctl mostly just don't work in Docker, and you should totally ignore them.

At the point where your entrypoint script is running, it is literally the only thing that is running. That means you don't need to restart nginx, because it hasn't started the first time yet. The standard pattern here is to use the entrypoint script to do some first-time setup; it will be passed the actual command to run as arguments, so you need to tell it to run them.

#!/bin/sh

echo "in entrypoint"
# ... do first-time setup ...

# ...then run the command, nginx or otherwise
exec "$@"

(Try running docker run --rm -it myimage /bin/sh. You will get an interactive shell in a new container, but after this first-time setup has happened.)

The one thing you do lose in your Dockerfile is the default CMD from the base image (setting an ENTRYPOINT resets that). You need to add back that CMD:

COPY entrypoint.sh /entrypoint.sh
RUN chmod +x /entrypoint.sh
ENTRYPOINT ["/entrypoint.sh"]
CMD ["nginx", "-g", "daemon off;"]

You should keep the other settings from the base image, like ENV definitions and EXPOSEd ports.

Answer 2

this will work using service command:

echo "in entrypoint"

# I want to run some commands here... 

# After I want to run nginx normally....

nginx -t && service nginx reload

echo "after reload"

output:

in entrypoint
nginx: the configuration file /etc/nginx/nginx.conf syntax is ok
nginx: configuration file /etc/nginx/nginx.conf test is successful
Restarting nginx: nginx.
after reload

Answer 3

The "systemctl" command is specific to some SystemD based operating system. But you do not have such a SystemD daemon running on PID 1 - so even if you install those packages it wont work.

You can only check in the nginx.service file which command the "reload" would execute for real. Or have something like the docker-systemctl-replacement script do it for you.