Pushing an `aufs` Docker image into registry and pulling it onto an `overlay2` Docker installation. Possible?

Question

Now that Docker released an upgrade to version 23.0.0 I got an unfriendly reminder that three old Ubuntu installations were still configured to use aufs with Docker.

I had to revert to version 20.10.23 in order to be able to start my containers.

According to a chatbot, I can use docker save to export the content of the image, then upgrade the system to 23.0.0, and use docker load in order to recreate the image for use with the overlay2 driver.

Now my question is:

Is it possible to push the old, original, unsaved aufs images of the 20.10.23 version into a private registry, then upgrade the system to Docker version 23.0.0, and have docker run pull those old images for use with the overlay2 driver?

Could this cause an undefined behavior because the images in the registry were created with aufs, or is this a working migration path?

Answer 1

The Docker registry protocols and the docker save tar file formats are independent of any particular storage backend. If you (or your CI system) have an aufs Docker installation and push images to a registry, you shouldn't have any trouble pulling them on to an overlay2 setup.

Also consider that the registry protocol has only really had two major versions, but at various times devicemapper, aufs, overlay, and overlay2 have all been "the best" storage backend, and Docker Hub itself hasn't needed to do anything special to support this. Also of note is the appearance of alternate container runtimes like Podman, and Kubernetes's announcement that Docker proper is no longer a recommended container runtime, but these alternate systems still work file with existing image registries.