[ovirt-users] Engine migration and host import

Ben Bradley listsbb at virtx.net
Sun Sep 24 20:59:21 UTC 2017


On 23/09/17 00:27, Ben Bradley wrote:
> 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

So I tried again to migrate my bare-metal host to a hosted VM but no 
luck. The host remained in unresponsive state in the engine web UI and I 
was unable to manage the host in anyway. Although all VMs continued to run.

I did capture some logs though.
 From the new engine VM... engine.log
https://p.bsd-unix.net/view/raw/666839d1

 From the host...
mom.log  https://p.bsd-unix.net/view/raw/ac9379f0
supervdsm.log  https://p.bsd-unix.net/view/raw/f9018dec
vdsm.log  https://p.bsd-unix.net/view/raw/bcdcdb13

The engine VM is complaining about being unable to connect to the host, 
though I can see from tcpdump communication is fine. I believe this is 
backed up by the pings seen in mom.log

Though I can see the following in vdsm.log... [vds] recovery: waiting 
for storage pool to go up (clientIF:569)
So I wonder if this is blocking the engine bringing the host up.

The host is running local storage, which I believe is a pretty recent 
addition to ovirt. So I could see how trying to run an engine VM on a 
host's local storage might cause weird issues.

I realise that there won't be HA with this setup, until I create my 
second host and configure HA on the VM.

If I am unable to migrate from bare-metal -> engine VM then it doesn't 
give me any confidence that I would be able to restore a setup from a 
backup onto a bare-metal host and recover host state.

So is the only supported method of migrating from bare-metal engine to 
hosted engine by...
1) Migrating to the appliance
2) Using a new host to migrate to VM
3) Using shared storage between hosts

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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>>
>>
> 
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