I finally started implementing backup & restore feature for Puffin. The first issue I encountered was to make a backup of named volumes.

The official Docker documentation mentions only data volume containers and –volumes-from option. There’s also docker cp command, but it requires knowing the path where the volumes are mounted in the container that uses them.

It turns out it’s pretty easy to do using volume mounts and tar.

To backup some_volume to /tmp/some_archive.tar.bz2 simply run:

And to restore run:

I have chosen alpine image since it’s lightweight and contains everything what’s needed. One potential issue might be preserving file ownership since different users and groups exist on different containers. Classical solution to this problem is to run the tar command using the same image as the one normally using the volume instead of alpine, but what if there’s no tar there? Using numeric owner generally preserves permissions correctly, unless you also use user namespaces. Also you need to remember to stop all the containers using the volume being backed-up or restored, otherwise an inconsistent / intermediate state the data might be archived.

Ultimately I wrote my own little volume-backup utility for backup and restore of volumes that simplifies the process even further and offers some improvements. Example usage (see README for more details):

Feel free to check it out and let me know what do you think.

Edit: Changed the cleanup code to delete hidden files – thanks for a comment Olivier.

Edit: It’s also possible to backup to standard output and restore from standard input. I added this capability to volume-backup – thanks for a comment, suggestion and example Holger

Edit: Added –rm flag to remove the container when finished, thanks awade.