[ovirt-devel] upgrade of CL and DC vs running VMs

[Michal Skrivanek]

> On 25 May 2017, at 14:26, Oved Ourfali <oourfali at redhat.com> wrote:
> 
> 
> 
> On Thu, May 25, 2017 at 12:16 PM, Michal Skrivanek <mskrivan at redhat.com <mailto:mskrivan at redhat.com>> wrote:
> Hi all,
> I believe that introduction of bug 1413150 (Add warning to change CL to the match the installed engine version) may have an unfortunate consequence of people actually moving forward with the CL and DC without realizing the constraints on running existing VMs. The periodic nagging is likely going to make people run into the following issue even more frequently
> 
> 
> Shall we note on cluster upgrade operation that the user should be aware of the implications?

Cluster upgrade itself is not the problem (anymore), but we don’t have these checks and warning on DC upgrade.

> Do we know in advance those constraints and whether that are relevant in the environment, and if it is then not issue the warning?

Well, yeah, but when we were trying various way to “motivate” people to do it properly it didn't effectively work very well. It’ easy to miss/dismiss. Blocking worked….but was followed by a backlash and reverted

>  
> We have a cluster level override per VM which takes care of compatibility on CL update by setting the VM’s override to the original CL - that is visible in VM properties, but that’s pretty much it, it’s not very prominent at the moment and it can’t be searched on (bug 1454389). When the update cluster change is made there is a dialog informing you, and there’s also the pending config change for those running VMs…until you shut the VM down, from that time on it only has the CL override set.
> 
> But the real problem is with DC which AFAIK does not have an override capability, and currently does not have any checks for running VMs. With the above mechanism you can easily get a VM with CL override (say. 3.6) and mindlessly updated DC to 4.1…and once you stop such VM you won’t be able to start it anymore as there is a proper check for unsupported 3.6 CL VM in a newer DC (as implemented by bug 1436577 - Solve DC/Cluster upgrade of VMs with now-unsupported custom compatibility level)
> 
> I don't recall. Do we have a warning on data center level as well? Or only cluster level?
>  
> 
> We either need to warn/block on DC upgrade, or implement some kind of a DC override (I guess this is a storage question?)
> 
> (Similar to my question above), do we have a way to identify those constraints and whether they are relevant in the environment? And if so, block upgrading of the DC level?

Blocking is a possibility (e.g. when VMs are running with older CL override), but I do not know what are the dependent features, I suppose it’s mostly storage and network team’s features.

Thanks,
michal
>  
> 
> Thoughts/ideas?
> 
> Thanks,
> michal
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