Delete docker images from docker registry

Steps

Get Digest by pulling image

Use docker pull command can get image digest

docker pull registry.example.com/image_path/image:tag

If it is daily build for container backup purpose, the tag can be in date format, such as YYYYMMDD. The output can be

20210624: Pulling from image_path/image
...
22b5d63ad977: Already exists
8e2e66517d7e: Pull complete
Digest: sha256:7535af1f65524f9200b901fc31b9c779819e45c0502ef99605666842a319908f

Get Digest by deleting local image

The digest is also printed when deleting it.

docker rmi registry.example.com/image_path/image:tag

Sample output as below

Untagged: registry.example.com/image_path/image:tag
Untagged: registry.example.com/image_path/image@sha256:e300ff463dc18c7b3bf3964dc5a9832f613d829285a0da49e5fd37519dc7d0fc
Deleted: sha256:35baba3d5948b5844b67adcd6a236905039e929f8647d4e4afc9e64e9460d557
Deleted: sha256:bd681f3956f55dc028bae7ca4c2657457824a0e356c59705302fb084660a669b

Note: The Digest is the second tag, the sha256 in the first Deleted message is allowed to be deleted too, but the sha256 in the second Deleted message was not. Don't understand why

Get Digest by curl command

curl -v --silent -H "Accept: application/vnd.docker.distribution.manifest.v2+json" -X GET https://$USER:$PASSWORD@registry.example.com/v
2/image_path/image/manifests/tag 2>&1 | grep Docker-Content-Digest | awk '{print ($3)}'

Check manifests existence

curl https://$USER:$PASSWORD@registry.example.com/v2/image_path/image/manifests/sha256:xxxxxxxxxxxxxxxx

Delete tag

curl -X DELETE https://$USER:$PASSWORD@registry.example.com/v2/image_path/image/manifests/sha256:xxxxxxxxxxxxxxxx

Run garbage-collect

docker exec registry bin/registry garbage-collect --delete-untagged /etc/docker/registry/config.yml

Restart registry if necessary

docker restart registry