[libvirt-users] snapshots with virsh in a pacemaker cluster

[Lentes, Bernd]

Hi,

i have a two node cluster with virtual guests as resources.
I'd like to snapshot the guests once in the night and thought i had a procedure.
But i realize that things in a cluster are a bit more complicated than expected :-))

I will shutdown the guests to have a clean snapshot.
I can shutdown the guests via pacemaker.
But then arises the first problem:

When i issue a "virsh snapshot-create-as" libvirt needs the domain name as a parameter.
but libvirt does not know the domains any longer. When the guests are shutdown a "virsh list --all"
on both nodes does not show any domain.

A look in the respective resource agent VirtualDomain explains why:
The domain is started with virsh create:

"# The 'create' command guarantees that the domain will be
# undefined on shutdown, ...

OK: Now i could of course define all domains with a virsh define.

But then i have immediately the next problem. Now i'd create the snapshots with
"virsh snapshot-create-as" and starts the domains afterwards via cluster.
But let's assume i issue that on node 1 and some guests are started afterwards via pacemaker on node 2.
I can't predict on which node the guests are starting.

Then i don't get a snapshot, right ?

What to do ?

Bernd
--
Bernd Lentes
Systemadministration
Institut für Entwicklungsgenetik
Gebäude 35.34 - Raum 208
HelmholtzZentrum münchen
[ mailto:***@helmholtz-muenchen.de | ***@helmholtz-muenchen.de ]
phone: [phone]
fax: [phone]
[ http://www.helmholtz-muenchen.de/idg | http://www.helmholtz-muenchen.de/idg ]

wer Fehler macht kann etwas lernen
wer nichts macht kann auch nichts lernen


Helmholtz Zentrum Muenchen
Deutsches Forschungszentrum fuer Gesundheit und Umwelt (GmbH)
Ingolstaedter Landstr. 1
85764 Neuherberg
www.helmholtz-muenchen.de
Aufsichtsratsvorsitzende: NN
Stellv.Aufsichtsratsvorsitzender: MinDirig. Dr. Manfred Wolter
Geschaeftsfuehrer: Prof. Dr. med. Dr. h.c. Matthias Tschoep, Heinrich Bassler, Dr. rer. nat. Alfons Enhsen
Registergericht: Amtsgericht Muenchen HRB 6466
USt-IdNr: DE 129521671

[Peter Crowther]

Pacemaker always knows where its resources are running. Query it, stop the
domain, then use the queried location as the host to which to issue the
snapshot?

Cheers,

Peter

On Mon, 15 Oct 2018, 20:36 Lentes, Bernd, <

Post by Lentes, Bernd
Hi,
i have a two node cluster with virtual guests as resources.
I'd like to snapshot the guests once in the night and thought i had a procedure.
But i realize that things in a cluster are a bit more complicated than expected :-))
I will shutdown the guests to have a clean snapshot.
I can shutdown the guests via pacemaker.
When i issue a "virsh snapshot-create-as" libvirt needs the domain name as a parameter.
but libvirt does not know the domains any longer. When the guests are
shutdown a "virsh list --all"
on both nodes does not show any domain.
"# The 'create' command guarantees that the domain will be
# undefined on shutdown, ...
OK: Now i could of course define all domains with a virsh define.
But then i have immediately the next problem. Now i'd create the snapshots with
"virsh snapshot-create-as" and starts the domains afterwards via cluster.
But let's assume i issue that on node 1 and some guests are started
afterwards via pacemaker on node 2.
I can't predict on which node the guests are starting.
Then i don't get a snapshot, right ?
What to do ?
Bernd
--
Bernd Lentes
Systemadministration
Institut fÃŒr Entwicklungsgenetik
GebÀude 35.34 - Raum 208
HelmholtzZentrum mÃŒnchen
phone: [phone]
fax: [phone]
[ http://www.helmholtz-muenchen.de/idg |
http://www.helmholtz-muenchen.de/idg ]
wer Fehler macht kann etwas lernen
wer nichts macht kann auch nichts lernen
Helmholtz Zentrum Muenchen
Deutsches Forschungszentrum fuer Gesundheit und Umwelt (GmbH)
Ingolstaedter Landstr. 1
85764 Neuherberg
www.helmholtz-muenchen.de
Aufsichtsratsvorsitzende: NN
Stellv.Aufsichtsratsvorsitzender: MinDirig. Dr. Manfred Wolter
Geschaeftsfuehrer: Prof. Dr. med. Dr. h.c. Matthias Tschoep, Heinrich
Bassler, Dr. rer. nat. Alfons Enhsen
Registergericht: Amtsgericht Muenchen HRB 6466
USt-IdNr: DE 129521671
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[Lentes, Bernd]

Post by Peter Crowther
Pacemaker always knows where its resources are running. Query it, stop the
domain, then use the queried location as the host to which to issue the
snapshot?

But can i be sure that the resource starts on the node it was running before ?
IMHO no.
What is if i start the snapshot on node A but the resource starts afterwards on node B ?
Then libvirt on node B does not know it should perform a snapshot.

Post by Peter Crowther
On Mon, 15 Oct 2018, 20:36 Lentes, Bernd, < [

Post by Lentes, Bernd
Hi,
i have a two node cluster with virtual guests as resources.
I'd like to snapshot the guests once in the night and thought i had a procedure.
But i realize that things in a cluster are a bit more complicated than expected :-))
I will shutdown the guests to have a clean snapshot.
I can shutdown the guests via pacemaker.
When i issue a "virsh snapshot-create-as" libvirt needs the domain name as a parameter.
but libvirt does not know the domains any longer. When the guests are shutdown a
"virsh list --all"
on both nodes does not show any domain.
"# The 'create' command guarantees that the domain will be
# undefined on shutdown, ...
OK: Now i could of course define all domains with a virsh define.
But then i have immediately the next problem. Now i'd create the snapshots with
"virsh snapshot-create-as" and starts the domains afterwards via cluster.
But let's assume i issue that on node 1 and some guests are started afterwards
via pacemaker on node 2.
I can't predict on which node the guests are starting.
Then i don't get a snapshot, right ?
What to do ?
Bernd

Helmholtz Zentrum Muenchen
Deutsches Forschungszentrum fuer Gesundheit und Umwelt (GmbH)
Ingolstaedter Landstr. 1
85764 Neuherberg
www.helmholtz-muenchen.de
Aufsichtsratsvorsitzende: NN
Stellv.Aufsichtsratsvorsitzender: MinDirig. Dr. Manfred Wolter
Geschaeftsfuehrer: Prof. Dr. med. Dr. h.c. Matthias Tschoep, Heinrich Bassler, Dr. rer. nat. Alfons Enhsen
Registergericht: Amtsgericht Muenchen HRB 6466
USt-IdNr: DE 129521671

[Doug Hughes]

I snapshot my guests live with qemu-guest-agent. It works pretty much
flawlessly with qcow2, but even with raw I can almost always boot off of
a snapshot. I combine this with zfs and hourly snapshots and replication
and have a really usable backup and DR system that works with my guests,
both Windows and Linux.

You should test it with qemu-guest-agent and then try to boot off of it
and see if you run into issues. I've been doing this for 2+ years.

Post by Lentes, Bernd
Hi,
i have a two node cluster with virtual guests as resources.
I'd like to snapshot the guests once in the night and thought i had a procedure.
But i realize that things in a cluster are a bit more complicated than expected :-))
I will shutdown the guests to have a clean snapshot.
I can shutdown the guests via pacemaker.
When i issue a "virsh snapshot-create-as" libvirt needs the domain name as a parameter.
but libvirt does not know the domains any longer. When the guests are shutdown a "virsh list --all"
on both nodes does not show any domain.
"# The 'create' command guarantees that the domain will be
# undefined on shutdown, ...
OK: Now i could of course define all domains with a virsh define.
But then i have immediately the next problem. Now i'd create the snapshots with
"virsh snapshot-create-as" and starts the domains afterwards via cluster.
But let's assume i issue that on node 1 and some guests are started afterwards via pacemaker on node 2.
I can't predict on which node the guests are starting.
Then i don't get a snapshot, right ?
What to do ?
Bernd