Snapshotting for rollback after updates was[ Re: Drawing lessons from fatal SELinux bug #1054350]

[Chris Murphy]

On Jan 25, 2014, at 4:12 PM, Adam Williamson <awilliam at redhat.com> wrote:
> 
> * Do an offline update that includes Foo v2.0
> * Boot the updated system, run Foo, it migrates its configuration to
> some new scheme
> * Realize there was something wrong with the update, roll it back
> * Run Foo again, find it doesn't work because it's been migrated to the
> new config scheme which the old version of Foo doesn't work with

I would grumble, but a configuration file being updated and made incompatible with the prior version would be tolerated. Ideally the application makes an unmodified copy. If it doesn't, new school restore with --reflink from snapshot, regular cp if using LVM thinp snapshots, and old school just restore the file from a conventional backup. Not such a big deal.

If it's something far less throw away than configuration files being changed, it's a bit more complicated how badly and quickly the conversation degrades. But I can hardly recall a recent example of this happening. It's just not that common in my experience.


Chris Murphy