Cleaning up GitLab container registry

Is your self-hosted GitLab's Docker container registry using more and more storage space even though you configured cleanup policies in your repositories?

$ du -hs /opt/gitlab-rails/shared/registry
305G /opt/gitlab-rails/shared/registry

You probably need to run registry garbage collection:

$ gitlab-ctl registry-garbage-collect --delete-manifests

This is a destructive operation so understand what it does before you run it! When you do, then put this in a daily or weekly cronjob and you're all set.

Tags → manifests → layers

In Docker, image tags are pointers to image manifests and manifests are pointers to layers. The layers use all the storage space. GitLab's repository cleanup policies remove tags, leaving manifests and layers behind.

Registry garbage collection deletes only unreferenced blobs by default. Therefore, to really reclaim storage space, you need to delete manifests that are no longer associated with any tags. This is what the --delete-manifests option does.

In our case, after a few years of use, we went from over 300GB down to 17GB. Nice.

$ du -hs /opt/gitlab-rails/shared/registry
17G /opt/gitlab-rails/shared/registry

Delete untagged?

Note there is also a seemingly undocumented --delete-untagged option to the garbage collector. An alias for --delete-manifests perhaps? Anyone know, or gutsy enough to try it out and share the results?

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