Use cache docker image for gitlab-ci

Question

I was wondering is it possible to use cached docker images in gitlab registry for gitlab-ci? for example, I want to use node:16.3.0-alpine docker image, can I cache it in my gitlab registry and pull it from that and speed up my gitlab ci instead of pulling it from docker hub?

Answer 1

Yes, GitLab's dependency proxy features allow you to configure GitLab as a " pull through cache ". This is also beneficial for working around rate limits of upstream sources like dockerhub.

It should be faster in most cases to use the dependency proxy, but not necessarily so. It's possible that dockerhub can be more performant than a small self-hosted server, for example. GitLab runners are also remote with respect to the registry and not necessarily any "closer" to the GitLab registry than any other registry over the internet. So, keep that in mind.

As a side note, the absolute fastest way to retrieve cached images is to self-host your GitLab runners and hold images directly on the host. That way, when jobs start, if the image already exists on the host, the job will start immediately because it does not need to pull the image (depending on your pull configuration). (that is, assuming you're using images in the image: declaration for your job)

Answer 2

I'm using a corporate Gitlab instance where for some reason the Dependency Proxy feature has been disabled. The other option you have is to create a new Docker image on your local machine, then push it into the Container Registry of your personal Gitlab project.

# First create a one-line Dockerfile containing "FROM node:16.3.0-alpine"
docker pull node:16.3.0-alpine
docker build . -t registry.example.com/group/project/image
docker login registry.example.com -u <username> -p <token>
docker push registry.example.com/group/project/image

where the image tag should be constructed based on the example given on your project's private Container Registry page.

Now in your CI job, you just change image: node:16.3.0-alpine to image: registry.example.com/group/project/image . You may have to run the docker login command (using a deploy token for credentials, see Settings -> Repository) in the before_script section -- I think maybe newer versions of Gitlab will have the runner authenticate to the private Container Registry using system credentials, but that could vary depending on how it's configured.