How do I check if an image:tag exists in gitlab container registry

Update: I added a solution that works without access to the docker server (non-privileged mode) below.

Ok, here is a solution I came up with using the docker:stable image by enabling the experimental client features.

mkdir -p ~/.docker
"echo '{\"experimental\": \"enabled\"}' > ~/.docker/config.json"
docker  login -u gitlab-ci-token -p $CI_JOB_TOKEN $CI_REGISTRY
docker  manifest inspect $IMGNAME:$IMGTAG > /dev/null && exit || true

The exit terminates the build script in case that tag already exists. Also you should be aware that ~/.docker/config.json is overwritten. That is also why the login must happen afterwards.

Update: Instead of writing to the config one can also set the DOCKER_CLI_EXPERIMENTAL environment variable to enabled. Thus the first two lines can be replaced with export DOCKER_CLI_EXPERIMENTAL=enabled

Update: If you don't have privileged mode turned on and thus no access to the docker-daemon, you can use the registry-api scripts provided by harbor ( Note that they are python2.). This comes handy if you are building a docker image using kaniko, where no access to the docker-daemon is needed.

Unless the GitLab Container Registry supports the kind of curl dockerhub does (with v1/repositories/$1/tags/$2), I doubt it offers that feature.

For instance, issue 26866 "GitLab Registry available images list/search" is still open after 10 months.

Update for GitLab 12.2 (April 2019, 18 months later)

After working through the implementation, it made sense to create two endpoints:

• GET /groups/:id/registry/repositories - Returns a list of all Docker container repositories for all projects within the group, similar to GET /projects/:id/registry/repositories

and

• GET /groups/:id/registry/repositories/tags - Returns a list of all Docker container repositories for all projects within the group including all tags for each container repository. The response will look something like this:

So that could help checking if an image:tag exists.

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Update GitLab 13.0 (May 2020)

Use search to quickly find and discover images hosted in the GitLab Container Registry

When you or someone on your team publishes an image to the GitLab Container Registry, you need a way to quickly find it and ensure the image was built properly.
If you’re using GitLab CI/CD to publish images with each build, it’s been very difficult to find an image efficiently within the current user interface. Instead, you’ve relied on the command line or the API.

We are excited to announce that in 13.0, we’ve added search functionality to the GitLab Container Registry.

Simply navigate to your project or group’s registry and enter an image name to see a list of all your images.

See documentation and issue.

Gitlab API can be used.

tag=tag_name
image=image_name
private_token=gitlab_private_token
project=project_number
repo_id=$(curl --header "PRIVATE-TOKEN: $private_token" "https://gitlab.com/api/v4/projects/$project/registry/repositories" | jq -c --arg regex ".*\\$image$" '.[] | select(.path | test($regex))'.id)

if [ $( curl --header "PRIVATE-TOKEN: $private_token" "https://gitlab.com/api/v4/projects/$project/registry/repositories/$repo_id/tags/$tag" | jq -r '.name' ) == "$tag" ] ; then
  echo "$tag exists"
else
  echo "$tag does not exist"
fi