RFC: Comfy - a CLI framework to bring the Ubuntu cloud feeling to snappy Ubuntu Core

[Martin Pitt]

Steve Langasek [2015-02-02 12:11 +0200]:
> With this bit of magic, there's no requirement to implement relocatable
> builds for any packages.  There is more up front work before we can start
> making use of this, but it works for all arbitrary sets of packages.  The
> only thing that an overlay wouldn't be able to do is remove a file from the
> system underlay; this is something to be aware of, but it's an extreme
> corner case that this would ever cause a problem in practice, and if it did
> it could be addressed by rather small changes to the source in the snap
> package.

There's quite a bit more, though. For example, postinst scripts won't
work; in other words, you can't enable sysvinit scripts or systemd
units or get DB initialization or similar stuff; many servers won't
work because they can't put their sockets into /var so that other
stuff can see it (normally it's r/o, and if they declare a private
overlay it will be invisible outside). Pretty much everything trying
to write into /etc/ will not work as it's either r/o or doesn't work
correctly due to our file bind mounts.

These are of course all fixable individually, but with our current
design there's no magic bullet to make software work OOTB which
assumes LSB/FHS.

None of that will be particularly relevant for the comfy use case of
course, which isn't about services but CLI programs. But comfy is a
rather special case in that regard -- the main point of snaps is to
provide services after all :)

Martin

-- 
Martin Pitt                        | http://www.piware.de
Ubuntu Developer (www.ubuntu.com)  | Debian Developer  (www.debian.org)
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