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Comment by matt_kantor | Hacker News Reader

This is what docker-pushmi-pullyu[1] does, using `ssh -R` as suggested by a sibling comment.

[1]: https://github.com/mkantor/docker-pushmi-pullyu

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.

Yeah, a few years ago I remember looking into whether I could expose image layers from the engine as a volume to mount directly into the registry, but at least at the time it seemed complex, and when I write tools like this simplicity is a primary goal.

As a mitigation docker-pushmi-pullyu caches pushed layers between runs[1]. More often than not I'm only changing upper layers of previously-pushed images, so this helps a lot. Also, since everything happens locally the push phase is typically quite fast even with cache misses (especially on an SSD), especially compared to the pull phase which is usually going over the internet (or another network).

[1]: https://github.com/mkantor/docker-pushmi-pullyu/pull/19/file...

That's also what the submitted tool does, I want to do the same thing just in the reverse direction. I just don't want to start extra containers on the prod machine.

No, the second one (docker-pushmi-pullyu) runs the registry on the build host.

I meant to reply to you, whoops.

docker-pushmi-pullyu does an extra copy from build host to a registry, so it is just the standard workflow.

I think Spegel does what I want (= serve images from the local cache as a registry), I might be able to build from that. It is meant to be integrated with Kubernetes though, making a simple transfer tool probably requires some adaptation.

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