[ovirt-devel] Relocating the vdsm upgrade logic into a new or existing service at boot time

[Fabian Deutsch]

----- Original Message -----
> On Thu, Apr 23, 2015 at 08:58:28AM -0400, Fabian Deutsch wrote:
> > Hey,
> > 
> > the logic which is run on vdsm upgrades is located in the specfile, and
> > thus run
> > when the rpm get's an update.
> > This is fine as long as rpm is involved (like when rpm or yum or dnf is
> > used), but it
> > becomes - and already is - an issue for flows where the upgrade happens
> > without
> > rpm, like on oVirt Node.
> > 
> > On oVirt Node the image for booting the host is getting replaced, we
> > currently mimic
> > the upgrade process of the specfile. But this error prone - we had a lot of
> > bugs around
> > this area (remember the problems with the hooks?), and we need to watch out
> > for changes
> > in the upgrade logic.
> > 
> > To simplify and especially unify the logic between Node and normal hosts,
> > I'd like to
> > discuss if the upgrade logic can be moved to a separate service or included
> > in one of the
> > existsing services.
> > 
> > The simplest approach to me would be top create a new service which is
> > started before
> > libvirtd and vdsmd/supervdsmd to run some logic if an upgrade of vdsm is
> > detected.
> > This habit - to do the upgrade logic during boot - is actually not new and
> > systemd
> > provides some helpers (ConditionNeedsUpdate=) around this to ease the
> > implementation.
> > 
> > Thoughts?
> 
> The problem is real: we have too much logic on %post and %postun
> scripts, and end up with upgrade bugs litterally on every release.
> 
> However, for non-node installation we still need to allow configuration
> after upgrade, but before next boot.

Can you tell what kind of configuration needs to be done after upgrade,
before the next reboot?

> This means that everything in %post
> should be converted into vdsm-tool "configurators".
> https://gerrit.ovirt.org/#/c/39823/3/vdsm.spec.in is one small step in
> that direction.

I agree, that change is exactly what I'm looking for.

> When Vdsm starts up, it performs several "upgrade" modules, which
> are used to upgrade vdsm-specific configurations. These too should
> operate properly also when run much after boot.
> 
> Hence, I'm not sure about the benefit of adding an early systemd
> service, but I may be missing something.

I was only thinking about the separate service, to make sure that
any service who's configuration file get's possibly updated (i.e.
libvirtd) has not yet been started.

But if vdsmd and the configurators take care to restart the service
who's configuration file got changed, then we do not need a separate
one.

- fabian