[atomic-devel] [idea] docker-ostree integrated storage

[Colin Walters <walters verbum org>]

This came up in a discussion elsewhere, just tossing it up on the list if anyone's interested:

> Doesn't this suggest that [Docker sharing] should be independent of the way
> images are constructed?  This could probably be implemented even today
> with overlayfs, by keeping a hash file farm and hard-linking that into
> the immutable base image, similar to what OSTree does.

The overlayfs backend right now does use hardlinks between base and derived,
relying on overlayfs copy-up to avoid "hardlink writethrough" - but 

What the above is suggesting is the "hidden ostree-izing" model.  It's
quite possible.    This would involve something like the overlayfs
backend being modified to read/write to the host ostree repo.

It'd be a bit messy as then docker's overlayfs backend would depend
on an OSTree setup - so it'd probably have to be optional.  

But a neat feature of this model is it would enable sharing with the *host*,
not just between containers.  For example if you have the exact same
/usr/lib64/libc-2.17.so or /usr/bin/bash objects in both, which would be quite common.

It would also enable dynamic sharing between independent containers
that have the same content - this would happen with e.g. new base images
generated from kickstarts instead of deriving from $distro base.