Ah neat I didn't know that podman has 'image scp'. Thank you for sharing. Do you think it was more straightforward to implement this in podman because you can easily access its images and metadata as files on the file system without having to coordinate with any daemon?

Docker and containerd also store their images using a specific file system layout and a boltdb for metadata but I was afraid to access them directly. The owners and coordinators are still Docker/containerd so proper locks should be handled through them. As a result we become limited by the API that docker/containerd daemons provide.

For example, Docker daemon API doesn't provide a way to get or upload a particular image layer. That's why unregistry uses the containerd image store, not the classic Docker image store.