F22 System Wide Change: RpmOstree - Server side composes and atomic upgrades

[Colin Walters]

On Tue, Jan 20, 2015, at 06:27 AM, Jan Zelený wrote:

> You are probably right, I might have misunderstood what you actually propose. 
> Does it mean that you actually don't require this part to be implemented at 
> all and you can go with what's in /var without any distribution-wide changes? 

Fedora 21 Atomic does work with a current F21 packageset.  For example Docker stores
state in /var/lib/docker, and no changes were required to the docker RPM or or rpm-ostree
for this.

(Although an aside, Fedora 21 Atomic also stores docker images in a LVM volume
 which means they would need special factory reset handling if the feature was
 implemented)

> In other words, do you propose this change to be gradually implemented where 
> it makes sense?

Right, on demand.  If there's a Fedora RPM that doesn't work with this scheme
and is desirable to use by a 3rd party or by the Fedora Atomic subproject, we'd
engage with the RPM maintainer to figure out a solution.

> Thank you for the additional explanation. Now I think that the problem is not 
> in what you want but in possibly ambiguous specification. What I'm afraid of is 
> that some people will use this opportunity to push through fully transient 
> /var.

There's a commit to OSTree which does make fully transient /var happen out of
the box if the underlying / is read-only:
https://git.gnome.org/browse/ostree/commit/?id=ff6883ca0655ac8844cd783caf6a7d8815515ba3

Which is pretty nice for some use cases, but definitely not the default =)

At a high level, I do agree this part of the change needs analysis, and
I'm glad you brought it up.  In the end I think the risk here is going to 
vary a lot per package.

For example, I need to look closely at the alternatives system.

But I certainly don't want to break the traditional install model - among other things, it's
going to be a while before rpm-ostree would be a usable way to run my desktop,
and also packages need to be backportable to older branches, etc.