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Comment by hutrdvnj | Hacker News Reader

A .tar file on a file server wouldn't suffice, because you have to store a bunch of metadata for that .tar file. But now you could argue that the metadata could just be a file next to the tar file. True, but container registries are kind of like that + optimization + some useful extra features. If you were to start from a simple file server and think about the stuff you need, then after some iterations you would actually end up with a container registry.

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Docker save (and presumably podman too) adds that metadata as a file in a tar. Each layer becomes a tar that is nested in the top level tar.

Indeed, registries don't do much more than what:

    docker image save foo:latest \
      | ssh pod docker image load

does (the stream is a docker tar archive with layers and metadata).

A container registry allows you to download multiple layer simultaneously and only those that you need (that you don't have in cache).

AFAIK this is how it worked with classical OS packages (think rpm/yum/apt/etc.)

Packages and metadata was all prepared for distribution over nothing more than static file hosting and http(s) to leverage as much existing infrastructure as possible.

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