[ovirt-users] Engine migration and host import

Fri Sep 22 23:27:00 UTC 2017

On 20/09/17 15:41, Simone Tiraboschi wrote:
> 
> On Wed, Sep 20, 2017 at 12:30 AM, Ben Bradley <listsbb at virtx.net 
> <mailto: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/
>     <https://www.ovirt.org/develop/developer-guide/engine/migrate-to-hosted-engine/>
>     and
>     https://www.ovirt.org/documentation/self-hosted/chap-Migrating_from_Bare_Metal_to_an_EL-Based_Self-Hosted_Environment
>     <https://www.ovirt.org/documentation/self-hosted/chap-Migrating_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.

Thank you for the reply.
I tried this again this evening - again it failed.

The host is present within the new engine but I am unable to manage it.
Host is marked as down but Activate is greyed out. I can get get into 
the "Edit" screen for the host and on right-click I get the following 
options:
- Maintenance
- Confirm Host has been Rebooted
- SSH Management: Restart and Stop both available
The VMs are still running and accessible but are not listed as running 
under the web interface. This time however I did lose access to the 
ovirtmgmt bridge and the web interface, running VMs and host SSH session 
were unavailable until I rebooted.
Luckily I left ovirt-engine service enabled to restart on boot so 
everything came back up.

The engine URL is a CNAME so I just re-pointed to the hostname of the VM 
just before running engine-setup after the restore.

This time though I have kept the new engine VM so I can power it up 
again and try and debug.

I am going to try a few times over the weekend and I have setup serial 
console access so I can do a bit more debugging.

What ovirt logs could I check on the host to see if the new engine VM is 
able to connect and sync to the host properly?

Thanks, Ben

> 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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