How to automatically start a service when running

问题:

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?

回答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

回答2:

In your Dockerfile, add at the last line

ENTRYPOINT service ssh restart && bash

It works for me

And this is the result:

root@ubuntu:/home/vagrant/docker/add# docker run -i -t ubuntu
 * Restarting OpenBSD Secure Shell server sshd   [ OK ]                                                                      
root@dccc354e422e:~# service ssh status
 * sshd is running

回答3:

There's another way to do it that I've always found to be more readable.

Say that you want to start rabbitmq and mongodb when you run it then your CMD would look something like this:

CMD /etc/init.d/rabbitmq-server start && \
    /etc/init.d/mongod start

Since you can have only one CMD per Dockerfile the trick is to concatenate all instructions with && and then use \ for each command to start a new line.

If you end up adding to many of those I suggest you put all your commands in a script file and start it like @larry-cai suggested:

CMD /start.sh

回答4:

Simple! Add at the end of dockerfile:

ENTRYPOINT service mysql start && /bin/bash

回答5:

In my case, I have a PHP web application being served by Apache2 within the docker container that connects to a MYSQL backend database. Larry Cai's solution worked with minor modifications. I created a entrypoint.sh file within which I am managing my services. I think creating an entrypoint.sh when you have more than one command to execute when your container starts up is a cleaner way to bootstrap docker.

#!/bin/sh

set -e

echo "Starting the mysql daemon"
service mysql start

echo "navigating to volume /var/www"
cd /var/www
echo "Creating soft link"
ln -s /opt/mysite mysite

a2enmod headers
service apache2 restart

a2ensite mysite.conf
a2dissite 000-default.conf
service apache2 reload

if [ -z "$1" ]
then
    exec "/usr/sbin/apache2 -D -foreground"
else
    exec "$1"
fi

回答6:

The following documentation from the Docker website shows how to implement an SSH service in a docker container. It should be easily adaptable for your service:

• https://docs.docker.com/engine/examples/running_ssh_service/

A variation on this question has also been asked here:

• Start sshd automatically with docker container

回答7:

I add the following code to /root/.bashrc to run the code only once,

Please commit the container to the image before run this script, otherwise the 'docker_services' file will be created in the images and no service will be run.

if [ ! -e /var/run/docker_services ]; then
    echo "Starting services"
    service mysql start
    service ssh start
    service nginx start
    touch /var/run/docker_services
fi

回答8:

Here is how I automatically start the MySQL service whenever the docker container runs.

On my case, I need to run not just MySQL but also PHP, Nginx and Memcached

I have the following lines in Dockerfile

RUN echo "daemon off;" >> /etc/nginx/nginx.conf
EXPOSE 80
EXPOSE 3306
CMD service mysql start && service php-fpm start && nginx -g 'daemon off;' && service memcached start && bash

Adding && bash would keep Nginx, MySQL, PHP and Memcached running within the container.

回答9:

docker export -o <nameOfContainer>.tar <nameOfContainer>

Might need to prune the existing container using docker prune ...

Import with required modifications:

cat <nameOfContainer>.tar | docker import -c "ENTRYPOINT service mysql start && /bin/bash" - <nameOfContainer>

Run the container for example with always restart option to make sure it will auto resume after host/daemon recycle:

docker run -d -t -i --restart always --name <nameOfContainer> <nameOfContainer> /bin/bash

Side note: In my opinion reasonable is to start only cron service leaving container as clean as possible then just modify crontab or cron.hourly, .daily etc... with corresponding checkup/monitoring scripts. Reason is You rely only on one daemon and in case of changes it is easier with ansible or puppet to redistribute cron scripts instead of track services that start at boot.