Comment 3 for bug 1843043

Something that can be used as a workaround for those affected - on the db master host you execute:

docker exec mariadb bash -c 'mariabackup --backup --target-dir /var/lib/mysql/backup/$(date +"%Y-%m-%d-%H-%M-%S") --user backup --password=<mariadb_backup_database_password>'

The full backup requires an empty directory as destination and creates it if it doesn't exist. The backup appears on your docker host in /var/lib/docker/volumes/mariadb/_data/backup.

You might consider that as base for rewriting the current backup logic. The old backup mechanism used a separate container and a dedicated named volume. This snippet, however, creates a backup folder in the mariadb volume itself. You might opt for adding a dedicated backup volume to the existing mariadb container.

Unfortunately, the kolla_docker.py doesn't allow a simple exec-like execution yet. That would make the change quite easy. Unless I miss the point of having it run in a separate container (which I tried and which caused too much trouble to follow that path).