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