CODEWITHSUNDEEP
mysqldockermariadb
David M. Karr
David M. Karr

Reputation: 15225

How to properly move a mariadb database from a container to the host

I have a smallish webapp running in a Docker container. It uses a mariadb database running in another container on the same box, based on the official "mariadb" image.

When I first set up these containers, I started the mariadb container using an "internal" database. I gave the "/var/lib/mysql" a volume name, but I didn't map it to a directory on the host ("-v vol-name:/var/lib/mysql"). Actually, I'm not even sure why I gave it a volume name. I set this up several months ago, and I'm not sure why I would have done that specifically.

In any case, I've concluded that having a database internal to the container wasn't a good idea. I've decided I really need to have the actual database stored on the host and use a volume mapping to refer to it. I know how to do this if I was setting this up from scratch, but now that the app is running, I need to move the database to the host and restart the container to point to that. I'm not certain of all the proper steps to make this happen.

In addition, I'm also going to need to set up a second instance of this application, using containers based on the same images. The second database will also be stored on the host, in a directory next to the other one. I can initialize the second db with the backup file from the first one, but I'll likely manually empty most of the tables in the second instance.

I did use mysqldump inside the container to dump the database, then I copied that backup file to the host.

I know how to set a volume mapping in "docker run" to map /var/lib/mysql in the container to a location on the host.

At this point, I'm not certain exactly what to do with this backup file so I can restart the container with the modified volume mapping. I know I can run "mysql dbname < backup.sql", but I'm not sure of the consequences of that.

Upvotes: 0

Views: 3025

Answers (1)

rickdenhaan
rickdenhaan

Reputation: 11328

While the container is running, run docker cp-a CONTAINER:/var/lib/mysql /local/path/to/folder to copy the MariaDB databases from the container to your local machine. Replace "CONTAINER" with the name or ID of your MariaDB container.

Once you've done that, you can stop the container and restart it binding /local/path/to/folder to the container's /var/lib/mysql path.

If you're using an older version of docker that does not support the -a or --archive flag, you can copy the files without that flag but you'll need to make sure that the folder on the host machine has the proper ownership: the UID and GID of the folder must match the UID and GID of the folder in the Docker container.

Note: if you're using SELinux, you might need to set the proper permissions as well, as the documentation for the MariaDB image states:

Note that users on host systems with SELinux enabled may see issues with this. The current workaround is to assign the relevant SELinux policy type to the new data directory so that the container will be allowed to access it:

$ chcon -Rt svirt_sandbox_file_t /my/own/datadir

Upvotes: 1

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