tail /thoughts

Backing up Docker volumes

Published on 2014-01-23

I remembered this morning how Linode now supports Docker with their latest default kernel. OC-ness urges kicked in so I decided to replace the custom kernel I was using with the new 3.12.6 one. Soon after I rebooted my vm, I ssh’d back to it and ran docker ps. My mouth was wide open as I stared at an empty list. Even docker images was displaying nothing. Docker somehow broke after I switched to the new kernel. But wait, I had backup! I previously did a docker export on my ghost-mysql container so it should be fine. First I cleared out /var/lib/docker and re-installed docker. Then, I ran docker import and checked its filesystem. Nope. /var/lib/mysql/ghost wasn’t there. I headed to #docker looking for answers and some good soul told me about how volumes are exempted from the container’s filesystem when exported. He also gave me a tip: link the volume to the container and tar it up. Which kinda looks like this if you do it from the docker cli:

sudo docker run -rm -i -volumes-from ghost-mysql ubuntu tar -cz /var/lib/mysql > ~/backups/ghost-mysql-`date +%s`.tgz

Good thing I suck at blogging and only have three measly posts. Also, Cloudflare was kind enough to cache my pages so it was easy to bring them back up again. And now I know how to properly backup my container volumes. All’s well that ends well.