[ovirt-users] upgrade hosted-engine os ( not hosts )

[Yedidyah Bar David]

On Wed, Jun 29, 2016 at 10:07 PM, Paul Groeneweg | Pazion
<paul at pazion.nl> wrote:
>
> I am looking for a way to get my hosted-engine running on el7 so I can
> upgrade to oVirt 4.0. Currently my hosts already run el7, but my
> hosted-engine is still el6.
>
> I read
> https://www.ovirt.org/documentation/how-to/hosted-engine-host-OS-upgrade/
> but this is only about the hosts.
>
> I read https://www.ovirt.org/documentation/how-to/hosted-engine/, but it
> only mentions upgrade of the hosted-engine software, not the OS.
>
> I understood I can do a fresh hosted-engine install, and then import my
> storage domain to the new hosted engine, but:
>
> - Do I need to restore my hosted engine database? ( like described here:
> http://www.ovirt.org/develop/developer-guide/engine/migrate-to-hosted-engine/
> )

You might not have to, if you only care about the imported VMs from your
storage. This will not keep other configuration, such as users/roles/permissions
etc.

> - Can I directly install hosted-engine 4.0 and then import the storage
> domain? Or should I install same hosted-engine version?

AFAIK 4.0 engine can import 3.6 storage domains without problem.

> - Do I first need another master storage domain or can I directly import my
> old master storage domain?

No idea. Even if you do, you can create a small empty one and later remove it.

> - When importing the storage domain what is the risk it fails ( I have
> backups, but it would cost a day to restore all )

No idea, but IIRC we got many successful reports and at most few failures
for this.

> - How long would import take? few minutes or hours? ( I want to keep down
> time as low as possible ).

Again no idea. Perhaps do some test?

>
> Another option would be upgrade the OS ( with redhat-upgrade-tool ) or is
> this a path for disaster?

Didn't work for us well, so we decided to not support it. If you decide to try,
make sure you test carefully beforehand. From ovirt's POV:
1. You'll need to handle postgresql upgrade.
2. Right after OS upgrade, you'll still have (I think) el6 packages
of the engine. It will hopefully be in a good-enough state for upgrade
to 4.0, but we didn't test this.
3. Specifically, if upgrade fails, rollback will most likely not work,
so you'll have to manually handle this - take a full vm backup and make
sure you can restore it.

>
> I hope someone can tell me how I can smoothly upgrade my hosted-engine up to
> el7 and run oVirt 4.

We are working on a tool/wizard to help with this process. It used to work,
but at some point it was decided that one of the actions it does is risky
and was blocked, thus the tool is broken currently.

You can invoke the tool by running: 'hosted-engine --upgrade-appliance'.
As noted above, this is currently broken.

There are several open bugs about it, e.g.:

https://bugzilla.redhat.com/show_bug.cgi?id=1319457
https://bugzilla.redhat.com/show_bug.cgi?id=1343425
https://bugzilla.redhat.com/show_bug.cgi?id=1343593 (closed, this is
what broke the tool)

Basically, you can manually do what the tool is supposed to do:
1. Make sure state is clean and stable (no running/pending storage actions,
no VMs in the middle of migration etc), all clusters are compat level 3.6, etc.
2. Move to global maintenance
3. backup the engine using engine-backup and keep the backup elsewhere
4. Reinstall engine vm with el7 and 4.0 engine (the tool will use the engine
appliance, you might too but not sure how exactly).
5. Restore the backup and run engine-setup.
6. If all looks ok, leave global maintenance.

If you manually keep a full backup of the engine vm before step 4,
you might be able to restore this backup if there are problems.
Doing this in the provided tool is currently the main blocking issue
for it. Hopefully will be provided in 4.0.1.

Best,
-- 
Didi