Remove Pull-Through Cache
The pull-through cache allows users to run a local registry as a pull-through cache to an upstream registry. While this functionality is extremely useful, we have not made significant changes here, and our own blog uses the upstream version of the container registry. We don't have anything special to bring to the table for this functionality, and we can work with upstream to introduce features and fix bugs that affect us. Removing this allows us to also remove the client code, which similarly exists on upstream. Fundamentally, we can lose the maintenance burden of this code without sacrificing functionality.
We'd be able to remove ~7400 lines of code by removing this feature: https://gitlab.com/gitlab-org/container-registry/-/tree/818/proxy