On Thu, May 17, 2018 at 2:00 AM, Nir Soffer <nsoffer@redhat.com> wrote:

On Wed, May 16, 2018 at 7:37 PM Michael Watters <wattersm@watters.ws> wrote:
Is it possible to have multiple engines with different versions of ovirt
running in the same cluster? I am working on a plan to upgrade our
ovirt cluster to the 4.2 release however we would like to have a
rollback plan in case there are issues with the new engine.

You can run multiple engines, each on a different host (or vm). Then
you can remove entities from one engine and add them to the other.
If something goes wrong, you can move the entities back to the orignal
engine.

I think the new DR support can make this process easy and robust,
but not sure it works with older engine versions.

DR supports engine 4.2 and above, but the usecase is a bit different than what's described.

You can try to use replicated storage domains in the new setup, and then try to register those VMs and upgrade them to cluster 4.2

If any problem will occur you can shutdown the hosts in the new setup and start the old setup back again.

Adding Maor to add more info on this direction.

I think that hosted engine upgrade flow may also be useful, dumping
engine database on the old engine, and restoring it to a new engine,
and it may work better for upgrading between different versions.

Simone is the expert in this area.

Nir