MariaDB never starts within docker image - mysql

Question

I'm creating a docker image with ubuntu trusty and MariaDB 5.5 but I can never get MariaDB to start unless I actually connect to the running VM.
Dockerfile:
FROM ubuntu:trusty
# Upgrade packages
RUN apt-get update && apt-get upgrade -y
# So we can add a repo to apt
RUN apt-get install -y software-properties-common
# Add MariaDB repo to aptitude
RUN apt-key adv --recv-keys --keyserver hkp://keyserver.ubuntu.com:80 0xcbcb082a1bb943db
RUN add-apt-repository 'deb http://mirror.jmu.edu/pub/mariadb/repo/5.5/ubuntu trusty main'
RUN apt-get update
# Install MariaDB
RUN DEBIAN_FRONTEND=noninteractive debconf-set-selections << 'mariadb-server-5.5 mysql-server/root_password password PASS'
RUN DEBIAN_FRONTEND=noninteractive debconf-set-selections << 'mariadb-server-5.5 mysql-server/root_password_again password PASS'
RUN DEBIAN_FRONTEND=noninteractive apt-get install -y mariadb-server
# Start MariaDB
RUN service mysql start
# Configure MariaDB User permissions
RUN echo "CREATE USER 'ubuntu'#'localhost'" | mysql -u root
The command I'm running to create:
docker build -t ebth-com-trusty --file `pwd`/Dockerfile `pwd` --no-cache
The create command will always fail due to:
ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/var/run/mysqld/mysqld.sock' (111)
But if I comment out the CREATE USER command, and then connect to the VM, I can connect to MariaDB just fine after running a manual service mysql start.
It is as if the RUN service mysql start just doesn't work, and I'm not sure how to debug this any further.

Answer 1

Every command in a Dockerfile is run in it's own container.
You can think of the process like:
new container is spun up using the previous image
the command is executed
the container is spun down
an image of that container is taken for the next command to run on
This means that the command RUN service mysql start will spin up a new container, start MariaDB, then shut down the container including shutting down MariaDB.
Instead try using CMD and ENTRYPOINT. You can think of them as setting the default executable, command and parameters executed once the container is spun up. However, the difference between the two is a bit more neuanced. Check out the docs: CMD and ENTRYPOINT
It would look something like this:
# Create default user
RUN service mysql start && \
echo "CREATE USER 'ubuntu'#'localhost'" | mysql -u root
# Start MariaDB
ENTRYPOINT ["/bin/bash"]
CMD ["service", "mysql", "start"]