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From Marcus <shadow...@gmail.com>
Subject Re: Need Info on configuring cloudstack HA
Date Mon, 03 Aug 2015 19:53:12 GMT
yes, the HA function is not very hypervisor specific. If the mgmt server
thinks that a vm that is marked 'HA' is not running and should be, it will
try to start it, with whatever hypervisors are available. No setup needed
on KVM.

If the KVM agent decides it cannot write to a primary NFS storage, it will
hard reboot the hypervisor. This gives a chance for another hypervisor to
start up the VM, but it currently requires that the rebooted hypervisor
come back online. So for NFS storage you have a little better chance of
recovering a VM due to an isolated storage outage between a hypervisor and
its storage.

The only real scenario where KVM HA works is when the affected hypervisor
successfully reboots and the agent reconnects to the mgmt server. When this
happens, it tells the mgmt server that the hypervisor is not running the VM
any longer and the mgmt server starts the VM somewhere else. There is
nothing else short of fencing(which is not implemented yet) that guarantees
the VM is no longer running on that hypervisor and safe to start elsewhere
without risk of corruption. Any ping tests could simply reveal split brain,
and the KVM HA storage heartbeat could just reveal an intermittent storage
outage and the host could fail the agent request to reboot, leaving a VM
waiting to come back when the storage unblocks.

In the future, we want a way to fence the hypervisor (IPMI, PDU, or storage
ACL), if the fence succeeds then we can safely start the VM elsewhere.
Until then, we have to rely on the host coming back online and telling us
that the VM is off. The other alternative for an admin to do manually is to
delete the host from the cluster. This should set all of the VMs that were
running on it to 'Stopped', and is useful if the admin knows the host is
down and out and doesn't want to wait for the repair for cloudstack to
realize that it needs to start those VMs elsewhere.

On Mon, Aug 3, 2015 at 12:05 PM, Wido den Hollander <wido@widodh.nl> wrote:

>
>
> On 08/03/2015 05:58 PM, Nux! wrote:
> > Hello,
> >
> > "KVM" itself does not have a built-in HA engine, since it's just the
> hypervisor.
> >
> > The HA in this case is handled by the Cloudstack management server, it
> will make sure your instance is always UP as long as
> > the service offering has "Offer HA".
> > e.g.
> http://storage4.static.itmages.com/i/15/0803/h_1438617503_4305698_2ca336f081.png
> >
> > Obviously, HA assumes primary storage is usable from all hypervisors, so
> this means shared storage (NFS, CEPH, shared mount point etc), it will not
> work with local storage.
> >
>
> Keep in mind that ONLY when using NFS there will be a heartbeat written
> to the storage.
>
> Currently HA is the safest to use when there is at least one NFS primary
> storage available.
>
> Wido
>
> > HTH
> > Lucian
> >
> > --
> > Sent from the Delta quadrant using Borg technology!
> >
> > Nux!
> > www.nux.ro
> >
> > ----- Original Message -----
> >> From: "Mike Tutkowski" <mike.tutkowski@solidfire.com>
> >> To: dev@cloudstack.apache.org
> >> Cc: "Marcus Sorensen" <shadowsor@gmail.com>
> >> Sent: Monday, 3 August, 2015 16:13:01
> >> Subject: Fwd: Need Info on configuring cloudstack HA
> >
> >> CCing Marcus since he's one of our resident KVM gurus, but - of course -
> >> anyone please chime in.
> >>
> >> Thanks!
> >>
> >> ---------- Forwarded message ----------
> >> From: Budur Nagaraju <nbudoor@gmail.com>
> >> Date: Mon, Aug 3, 2015 at 1:44 AM
> >> Subject: Need Info on configuring cloudstack HA
> >> To: dev-owner@cloudstack.apache.org
> >>
> >>
> >> HI
> >>  New to cloud stack struggled searching for configuring KVM HA unable to
> >> find any document .
> >>  Pls any help to configure KVM HA in cloud stack ,really helps a lot.
> >>
> >> Thanks,
> >> Nagaraju
> >>
> >>
> >>
> >> --
> >> *Mike Tutkowski*
> >> *Senior CloudStack Developer, SolidFire Inc.*
> >> e: mike.tutkowski@solidfire.com
> >> o: 303.746.7302
> >> Advancing the way the world uses the cloud
> >> <http://solidfire.com/solution/overview/?video=play>*™*
>

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