[ovirt-users] Engine migration and host import

[Simone Tiraboschi]

On Wed, Sep 20, 2017 at 12:30 AM, Ben Bradley <listsbb at virtx.net> wrote:

> Hi All
>
> I've been running a single-host ovirt setup for several months, having
> previously used a basic QEMU/KVM for a few years in lab environments.
>
> I currently have the ovirt engine running at the bare-metal level, with
> the box also acting as the single host. I am also running this with local
> storage.
>
> I now have an extra host I can use and would like to migrate to a hosted
> engine. The following documentation appears to be perfect and pretty clear
> about the steps involved: https://www.ovirt.org/develop/
> developer-guide/engine/migrate-to-hosted-engine/ and
> https://www.ovirt.org/documentation/self-hosted/chap-Migrati
> ng_from_Bare_Metal_to_an_EL-Based_Self-Hosted_Environment
>
> However I'd like to try and get a bit more of an understanding of the
> process that happens behind the scenes during the cut-over from one engine
> to a new/hosted engine.
>
> As an experiment I attempted the following:
> - created a new VM within my current environment (bare-metal engine)
> - creating an engine-backup
> - stopped the bare-metal engine
> - restored the backup into the new VM
> - ran engine-setup within the new VM
> The new engine started up ok and I was able to connect and login to the
> web UI. However my host was "unresponsive" and I was unable to manage it in
> any way from the VM. I shut the VM down and started the bare-metal
> ovirt-engine again on the host and everything worked as before. I didn't
> try very hard to make it work however.
>
> The magic missing from the basic process I tried is the synchronising and
> importing of the existing host, which is what the hosted-engine utility
> does.
>

No magic up to now: the host are simply in the DB you restored.
If the VM has network connectivity and the same host-name of the old
machine you shouldn't see any issue.
If you changed the host-name moving to the VM, you should simply run
engine-rename after the restore.

The only detail is that hosted-engine-setup will try to add the host where
you are running it to the engine and so you have to manually remove it just
after the restore in order to avoid a failure there.



>
> Can anyone describe that process in a bit more detail?
> Is it possible to perform any part of that process manually?
>
> I'm planning to expand my lab and dev environments so for me it's
> important to discover the following...
> - That I'm able to reverse the process back to bare-metal engine if I ever
> need/want to
> - That I can setup a new VM or host with nothing more than an
> engine-backup but still be able to regain control of exiting hosts and VMs
> within the cluster
>
> My main concern after my basic attempt at a "restore/migration" above is
> that I might not be able to re-import/sync an existing host after I have
> restored engine from a backup.
>
> I have been able to export VMs to storage, remove them from ovirt,
> re-install engine and restore, then import VMs from the export domain. That
> all worked fine. But it involved shutting down all VMs and removing their
> definitions from the environment.
>
> Are there any pre-requisites to being able to re-import an existing
> running host (and VMs), such as placing ALL hosts into maintenance mode and
> shutting down any VMs first?
>
> Any insight into host recovery/import/sync processes and steps will be
> greatly appreciated.
>
> Best regards
> Ben
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