1.2. Environment variables

Why was there an error in the previous lab?
The MariaDB server cannot run without a proper configuration. Docker can pass configuration variables into the setup process via environment variables. Environment variables are passed with the -e parameter, as in:

docker run -it -e MARIADB_ROOT_PASSWORD=my-secret-pw mariadb

After running the command, you will see output similar to this:

Initializing database

PLEASE REMEMBER TO SET A PASSWORD FOR THE MariaDB root USER!
To do so, start the server, then issue the following commands:

'/usr/bin/mysqladmin' -u root password 'new-password'
'/usr/bin/mysqladmin' -u root -h <host> password 'new-password'

Alternatively, you can run:
'/usr/bin/mysql_secure_installation'

Notice that we used the arguments -it (interactive terminal). You may have also found that MariaDB does not respond to the usual CTRL-C. To exit, Docker provides an escape sequence to detach from a container while leaving it running: press CTRL-p, then CTRL-q. In some web shells, these shortcuts may not work, so close the terminal and reopen it to continue.

To verify the container is running, use:

docker ps

Output should look like this:

CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS              PORTS               NAMES
7cb31f821233        mariadb             "docker-entrypoint..."   5 minutes ago       Up 5 minutes        3306/tcp            upbeat_blackwell

Accessing the container

To reconnect to the container, use:

docker exec -it <container> bash

Here, <container> can be the CONTAINER ID (typically the first two characters suffice) or the NAMES from docker ps. In the example above, this could be 7cb31f821233 or upbeat_blackwell.

Executing the command should display:

root@7cb31f821233:/#

Now that we’re connected, let’s check if MariaDB is working:

mariadb -uroot -pmy-secret-pw

If successful, the MariaDB command line should appear:

Welcome to the MariaDB monitor. Commands end with ; or \g.
...
MariaDB [(none)]>

Type exit; to leave the MariaDB client, then type exit again to leave the container.

Detached containers

Running a Docker container in “detached” mode (background) can be done with -d:

docker run -it -e MARIADB_ROOT_PASSWORD=my-secret-pw -d mariadb

Now, instead of seeing container logs, only the container ID is displayed. Verify by listing running containers:

docker ps

Stop any container as needed:

docker stop <container>

Or, to remove a container, use:

docker rm <container>

For a complete list, including stopped containers:

docker ps --all

Mounting a volume in a container

The MariaDB container is a good example for using a persistent volume. We’ll create a Docker-managed volume for persistent MariaDB data:

docker volume create volume-mariadb
docker run --name mariadb-container-with-external-volume -v volume-mariadb:/var/lib/mysql -e MARIADB_ROOT_PASSWORD=my-secret-pw -d mariadb

Inspect your volume with:

docker volume inspect volume-mariadb

To add a new user to MariaDB, connect and run:

docker exec -it mariadb-container-with-external-volume mariadb -uroot -pmy-secret-pw

Inside MariaDB:

use mysql;
CREATE USER 'peter'@'%' IDENTIFIED BY 'venkman';
GRANT SELECT ON mysql.user TO 'peter'@'%';

Now quit MariaDB and the container:

exit

By using volumes, we have persisted the data in our database!