Installing and using MariaDB via Docker
Sometimes we want to install a specific version of MariaDB, MariaDB Galera Cluster, or MaxScale on a certain system, but no packages are available. Or maybe, we simply want to isolate MariaDB from the rest of the system, to be sure that we won't cause any damage.
A virtual machine would certainly serve the scope. However, this means installing a system on the top of another system. It requires a lot of resources.
In many cases, the best solution is Docker. Docker is a framework that runs containers. A container is meant to run a specific daemon, and the software that is needed for that daemon to properly work. Docker does not virtualize a whole system; a container only includes the packages that are not included in the underlying system.
Docker requires a very small amount of resources. It can run on a virtualized system. It is used both in development and in production environments.
Docker is an open source project, released under the Apache License, version 2.
Note that, while your package repositories could have a package called
docker, it is probably not the Docker we are talking about. The Docker package could be called
Downloading an image
You can download a MariaDB image for Docker from the official repository, or choose another image that better suits your needs. You can search Docker Hub (the official set of repositories) for an image with this command:
docker search mariadb
Once you have found an image that you want to use, you can download it via Docker. Some layers including necessary dependencies will be downloaded too. Note that, once a layer is downloaded for a certain image, Docker will not need to download it again for another image.
For example, if you want to install the default MariaDB image, you can type:
docker pull mariadb
You will see a list of necessary layers. For each layer, Dockers will say if it is already present, or its download progress.
To get a list of installed images:
docker ps -a
Creating the container
An image is not a running process; it is just the software needed to be launched. To run it, we must create a container first. The command needed to create a container can usually be found in the image documentation. For example, to create a container for the official MariaDB image:
docker run --name mariadb-10.0 -e MYSQL_ROOT_PASSWORD=mypass -d mariadb
mariadb-10.0 is the name we want to assign the container. If we don't specify a name, an id will be automatically generated.
Optionally, after the image name, we can specify some options for mysqld. For example:
docker run --name mariadb-10.0 -e MYSQL_ROOT_PASSWORD=mypass -d mariadb --log-bin --binlog-format=MIXED
Docker will respond with the container's id. But, just to be sure that the container has been created and is running, we can get a list of running containers in this way:
We should get an output similar to this one:
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES 819b786a8b48 mariadb "/docker-entrypoint. 4 minutes ago Up 4 minutes 3306/tcp mariadb-10.0
Running and stopping the container
Docker allows us to restart a container with a single command:
docker restart mariadb-10.0
The container can also be stopped like this:
docker stop mariadb-10.0
The container will not be destroyed by this command. The data will still live inside the container, even if MariaDB is not running. To restart the container and see our data, we can issue:
docker start mariadb-10.0
docker stop, the container will be gracefully terminated: a
SIGTERM signal will be sent to the
mysqld process, and Docker will wait for the process to shutdown before returning the control to the shell. However, it is also possible to set a timeout, after which the process will be immediately killed with a
SIGKILL. Or it is possible to immediately kill the process, with no timeout.
docker stop --time=30 mariadb-10.0 docker kill mariadb-10.0
In case we want to destroy a container, perhaps because the image does not suit our needs, we can stop it and then run:
docker rm mariadb-10.0
Troubleshooting a container
If the container doesn't start, or is not working properly, we can investigate with the following command:
docker logs mariadb-10.0
This command shows what the daemon sent to the stdout since the last attempt of starting.
Accessing the container
Most MariaDB images, including the official one, have the skip-networking option set in their my.ini file. To use MariaDB we will need to edit the configuration file and restart the container.
To access the container via Bash, we will run this command:
docker exec -it mariadb-10.0 bash
Now we can use normal Linux commands like cd, ls, etc. We will have root privileges. We can even install our favourite file editor, for example:
apt-get install vim
In some images, no repository is configured by default, so we may need to add them.
Connecting to MariaDB from outside
After modifying the my.cnf file, we will be able to connect to MariaDB from outside the container. Even other Docker containers will be able to connect to each other - for example, to form a Galera cluster.
There is a small caveat. When we try to connect to
localhost, the MariaDB library will try to use MariaDB's socket file in our system. But that file is in the container, so it will not be found. We will need to use 127.0.0.1 (IPv4) or ::1 (IPv6).
When running a cluster or a replication setup via Docker, we will want the containers to use different ports. The fastest way to achieve this is mapping the containers ports to different port on our system. We can do this when creating the containers (
docker run command), by using the
-p option, several times if necessary. For example, for Galera nodes we will use a mapping similar to this one:
-p 4306:3306 -p 5567:5567 -p 5444:5444 -p 5568:5568