Controlling both the builder and the registry is super nice btw, because they can work together. If the builder knows some of the layers already exist in the registry, it merely has to create and push the remaining ones (without downloading any of the other layers, not even those from the base image). That gives you near-instant builds once the biggest layers are cached in the registry!

Since builds usually happen in CI, and pulls happen elsewhere (e.g., a kubernetes node), in the end layers are only downloaded when the resulting container image is actually used.