The problem with running a registry locally is that Docker doesn't provide an API to get individual image layers to be able to build a registry API on top. You have to hook into the containerd Docker uses under the hood. You can't do this locally in many cases, for example, on macOS the VM running Docker Desktop doesn't expose the containerd socket. I guess the workaround you implemented in docker-pushmi-pullyu is an extra copy to the registry which is a bummer.