How to automatically start a service when running a docker container?

Question

I have a Dockerfile to install MySQL server in a container, which I then start like this:

sudo docker run -t -i 09d18b9a12be /bin/bash

But the MySQL service does not start automatically, I have to manually run (from within the container):

service mysql start

How do I automatically start the MySQL service when I run the docker container?

Answer 1

First, there is a problem in your Dockerfile:

RUN service mysql restart && /tmp/setup.sh

Docker images do not save running processes. Therefore, your RUN command executes only during docker build phase and stops after the build is completed. Instead, you need to specify the command when the container is started using the CMD or ENTRYPOINT commands like below:

CMD mysql start

Secondly, the docker container needs a process (last command) to keep running, otherwise the container will exit/stop. Therefore, the normal service mysql start command cannot be used directly in the Dockerfile.

Solution

There are three typical ways to keep the process running:

• Using service command and append non-end command after that like tail -F

  CMD service mysql start && tail -F /var/log/mysql/error.log
  

This is often preferred when you have a single service running as it makes the outputted log accessible to docker.

• Or use foreground command to do this

  CMD /usr/bin/mysqld_safe
  

This works only if there is a script like mysqld_safe.

• Or wrap your scripts into start.sh and put this in end

  CMD /start.sh
  

This is best if the command must perform a series of steps, again, /start.sh should stay running.

Note

For the beginner using supervisord is not recommended. Honestly, it is overkill. It is much better to use single service / single command for the container.

BTW: please check https://registry.hub.docker.com for existing mysql docker images for reference