# Is the docker registries garbage collection garbage?

Step 1) Run garbage collection on my registry

    docker-compose exec registry bin/registry garbage-collect /etc/docker/registry/config.yml
    ....
    4005 blobs marked, 0 blobs and 0 manifests eligible for deletion

So everything seems used in some image:tag.

Step 2) Check size

    du -sch $(docker volume inspect registry_registry -f "{{.Mountpoint}}")
    50G     /var/lib/docker/volumes/registry_registry/_data

This is big, for the amount of images in there.
It's 73 images, all originating in the same base images.
Everything is either alpine or debian.

Step 3) Build a list of all images and all tags, download everything

    python list-all-repos.py --registry ... --ask-pass > all-repos
    for img in $(cat all-repos); do docker pull $img; done

(See below for script source)

Step 4) Throw away all registry data

    docker-compose down -v && docker-compose up -d

Step 5) Upload everything again

    for img in $(cat all-repos); do docker push $img; done

Now that everything is up again, I checked that all images are there again.
Just ran the script again and diffed the output. No differences.

Step 6) Check size again

    du -sch $(docker volume inspect registry_registry -f "{{.Mountpoint}}")
    6.4G    /var/lib/docker/volumes/registry_registry/_data

    ...garbage-collect
    473 blobs marked, 0 blobs and 0 manifests eligible for deletion

So, what am I not getting? Shouldn't GC already have thrown away everthing
not referenced by some image:tag?

## The script to list all images

This depends on [DXF](https://github.com/davedoesdev/dxf)

```python
"""Print all images and tags from given docker registry."""
import os
import argparse
import getpass

from dxf import DXF, DXFBase


def _get_arguments():
    parser = argparse.ArgumentParser(
        description="Print all images and tags from registry."""
    )
    parser.add_argument('--registry', dest='registry')
    parser.add_argument('--username', dest='username',
                        help="Defaults to $REGISTRY_USERNAME")
    parser.add_argument('--password', dest='password',
                        help="Defaults to $REGISTRY_PASSWORD")
    parser.add_argument('--ask-pass', dest='ask_pass', action='store_true',
                        help='Interactively ask for password')
    return parser.parse_args()


def main(registry, username, password):
    """Print all images and tag."""
    regbase = DXFBase(registry)
    regbase.authenticate(username, password)

    for repo in regbase.list_repos():
        regrepo = DXF(registry, repo)
        regrepo.authenticate(username, password)
        aliases = regrepo.list_aliases()
        for alias in aliases:
            print(f"{registry}/{repo}:{alias}")


if __name__ == "__main__":
    args = _get_arguments()
    _username = (args.username if args.username else
                 os.environ.get('REGISTRY_USERNAME'))
    if args.ask_pass:
        _password = getpass.getpass(f"{args.registry} password: ")
    else:
        _password = (args.password if args.password else
                     os.environ.get('REGISTRY_PASSWORD'))
    main(
        args.registry,
        _username,
        _password,
    )
```