delete image from docker registry v2 - docker

Question

the Docker Registry v2 has an API endpoint to delete an image
DELETE /v2/<name>/manifests/<reference>
https://github.com/docker/distribution/blob/master/docs/spec/api.md#deleting-an-image
However the doc says:
For deletes, reference must be a digest or the delete will fail.
Indeed, using a tag does not work and returns a 405 Operation Not Supported
The problem is, there doesn't seem to be any endpoint to get the digest of an image.
The endpoints to list images, and tags only list those.
Trying to get the manifest with
GET /v2/<name>/manifests/<reference>
using the tag as <reference>I see that a Docker-Content-Digest header is set with a digest which the doc says is
Docker-Content-Digest: Digest of the targeted content
for the request.
while the body contains a bunch of blobSum: <digest>
If I try using the Header digest value, with
GET /v2/<name>/manifests/<reference>
and the digest as <reference>, I get a 404.
the digest looks like: sha256:6367f164d92eb69a7f4bf4cab173e6b21398f94984ea1e1d8addc1863f4ed502
and I tried with and without the sha256 prefix. but no luck
So how am I supposed to get the digest of the image I want to delete, to delete it?

Answer 1

curl -u login:password -H "Accept: application/vnd.docker.distribution.manifest.v2+json" -X GET https://registry.private.com/v2/<name>/manifests/<tag>
json > config > digest

Answer 2

Not a trivial operation in Docker API right now but I hope this procedure helps:
Create a file and give it a name, for me it will be delete-image.sh:
#!/bin/bash
# Inspired by: https://gist.github.com/jaytaylor/86d5efaddda926a25fa68c263830dac1
set -o errexit
if [ -z "$1" ]
then
echo "Error: The image name arg is mandatory"
exit 1
fi
registry='localhost:5000'
name=$1
curl -v -sSL -X DELETE "http://${registry}/v2/${name}/manifests/$(
curl -sSL -I \
-H "Accept: application/vnd.docker.distribution.manifest.v2+json" \
"http://${registry}/v2/${name}/manifests/$(
curl -sSL "http://${registry}/v2/${name}/tags/list" | jq -r '.tags[0]'
)" \
| awk '$1 == "Docker-Content-Digest:" { print $2 }' \
| tr -d $'\r' \
)"
Give the permission to that file so that it can be executed;
sudo chmod u+x ./delete-image.sh
./delete-image.sh <your-image-name>
After deleting the image, collect the garbage;
docker exec -it registry.localhost bin/registry \
garbage-collect /etc/docker/registry/config.yml
Now delete the folder for that image (and I'm assuming that you created a volume previously);
sudo rm -rf ${HOME}/registry/docker/registry/v2/repositories/<your-image-name>
If you have not created a volume, you may have to enter the container to delete that folder. But, in any case, it's a good idea to restart the container;
docker restart registry.localhost
Procedure not recommended for production environments.
I hope that we will have better support for these operations natively in the Docker API in the future.