Even with Docker you need to care about backups.. ;-)

As you usually mount all the persistent data into the container the files will actually be on your host. Thus, you can simply do the backup of these files. However, for MySQL I prefer having an actual SQL-dump. Therefore I just developed the Docker MySQL-Backup tool. You will find the sources at the corresponding GitHub repository.

How does Docker MySQL-Backup work?

The tool basically consists of two scripts:

The script /etc/cron.daily/docker-mysql-backup parses the output of the docker ps command to find running containers of the MySQL image. More precisely, it looks for containers of images that start with \smysql. That of course only matches the original MySQL image names (if you have a good reason to derive an own version of that image please tell me!). For every matching $container the script will exec the following command:

docker exec "$container" \
	sh -c 'exec mysqldump --all-databases -uroot -p"$MYSQL_ROOT_PASSWORD"' \
	| ${GZIP} -9 > "${BACKUP_DIR}/${NOW}_complete.sql.gz"

With the following variables:

  • $BACKUP_DIR is a concatenation of $BACKUP_BASE (configured in /etc/default/docker-mysql-backup) and the container name,
  • $NOW is the current time stamp as date +"%Y-%m-%d_%H-%M".

Thus, the backups are compressed, organised in subdirectories of $BACKUP_BASE, and the SQL-dumps have a time stamp in their names. $BACKUP_BASE defaults to /srv/backup/mysql/, but can be configured in /etc/default/docker-mysql-backup.

Last but not least, the script also cleans the backups itself. It will keep the backups of the last 30 days and all backups of days that end with a 2. So you will keep the backups from the 2nd, the 12th, and the 22nd of every month.

As the script is stored in /etc/cron.daily/ the cron tool will execute the backup script on a daily basis.

Restore a dump

Restoring the dump is quite easy. Let’s assume your container’s name is $container and the dump to restore carries the time stamp $date. Then you just need to run:

docker exec "$container" -v "${BACKUP_BASE}/docker_${container}":/srv sh -c \
      'exec gunzip < /srv/${date}_complete.sql.gz | mysql -uroot -p"$MYSQL_ROOT_PASSWORD"'

This will mount the backup directory in /srv of the running container and then decompress and import the SQL-dump on the fly.


Manual installation through GitHub

Clone the Docker MySQL-Backup repository:

git clone https://github.com/binfalse/docker-mysql-backup.git

Copy the backup script to the cron.daily (most likely /etc/cron.daily/) directory on your system:

cp docker-mysql-backup/etc/cron.daily/docker-mysql-backup /etc/cron.daily/

Copy the configuration to /etc/default/:

cp docker-mysql-backup/etc/default/docker-mysql-backup /etc/default/

Installation from my Apt repository

If you’re running a Debian-based system you may want to use my apt-repository to install the Docker MySQL-Backup tool. In that case you just need to run

aptitude install bf-docker-mysql-backup

Afterwards, look into /etc/default/docker-mysql-backup for configuration options. This way, you’ll always stay up-to-date with bug fixes and new features :)

Martin Scharm

stuff. just for the records.

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