[PVE-User] Live VM migration 6.3 to 6.2 fails

[Christian Balzer]

On Wed, 2 Dec 2020 09:17:44 +0100 (CET) Daniel Berteaud wrote:

> ----- Le 2 Déc 20, à 9:11, Christian Balzer chibi at gol.com a écrit :
> 
> > Hello,
> > 
> > yes I know that migrating back to an older version is not guaranteed but
> > I'm rather confused as to why this happens.
> > 
> > Firstly this, more details below:
> > ---
> > 2020-12-02 16:34:08 start migrate command to tcp:10.0.0.11:60000
> > 2020-12-02 16:34:09 migration status error: failed
> > 2020-12-02 16:34:09 ERROR: online migrate failure - aborting
> > 2020-12-02 16:34:09 aborting phase 2 - cleanup resources
> > 2020-12-02 16:34:09 migrate_cancel
> > 2020-12-02 16:34:11 ERROR: migration finished with problems (duration 00:00:08)
> > TASK ERROR: migration problems
> > ---
> > 
> > That's all I get, where would one find the exact issue?
> > 
> > Now for the details, in the previous minor upgrade we saw a similar issue,
> > but that only affected VMs which had been created on an upgraded node, old
> > ones were fine to move in both ways.
> > OK, that was because of new features int he VM definition not present on
> > the old version, understandable.
> > 
> > With this one on a (more frequently updated) test cluster 6.3 to 6.2
> > migrations also works, the test cluster old nodes are at
> > pve-manager (6.2-12), the one with issues are pve-manager (6.2-6).
> > I however see nothing in the changelogs which would explain this difference.
> > 
> > In general being able to live migrate back to a node with the previous
> > version is a very desirable situation, since if there are issues/bugs (on
> > the VM level) with the new version there no longer is an impact free way
> > of reverting if this functionality is not present.
> >   
> 
> 
> That's most likely the QEMU version 5.1 on the 6.3 node vs QEMU 5.0 on the 6.2 one.
> There's no migration support from newer to older, only from older to newer.
> 
If that is really the case (qemu migrations between minor versions have
worked in the past, at least sometimes), then this is actually worse.

As I wrote, some 6.2 nodes don't have that issue and indeed they have qemu
5.1 which was brought in with 6.2-13. 
So no version upgrade flashing warning lights going off in your brain and
if one had not upgraded all nodes, the same would have happened in a
cluster that was nominally still 6.2?
That's rather... scary.

Christian

> Cheers,
> Daniel
> 
> -- 
> [ https://www.firewall-services.com/ ] 	
> Daniel Berteaud 
> FIREWALL-SERVICES SAS, La sécurité des réseaux 
> Société de Services en Logiciels Libres 
> Tél : +33.5 56 64 15 32 
> Matrix: @dani:fws.fr 
> [ https://www.firewall-services.com/ | https://www.firewall-services.com ]
> 
> 
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-- 
Christian Balzer        Network/Systems Engineer                
chibi at gol.com   	Rakuten Mobile Inc.