Re: [Xen-users] Failover

[Chris de Vidal <chris@xxxxxxxxxx>]

--- Matthijs ter Woord <matthijsterwoord@xxxxxxxxx> wrote:
> Is it possible to eliminate the possibility of a Xen host failure due to
> hardware failure (ie. failover clustering)?

I'm no Xen expert but from what I can tell you can't to high-availability with
the Xen kernel itself.

However, if you think about it, there is very little difference between domU
virtual machines and real machines.  You can easily do high-availability on
domU guests between two physical Xen hosts.  Run all of your services on domUs
and use something like UltraMonkey, regular LVS, Heartbeat, OpenSSI (assuming
it works with the domU kernel patches), or some other HA solution giving you
failover clustering.

The difference between this and a real cluster is only that Xen is running
below the virtual machines; very little is different.  They only add a thin
layer of separation.


So for example if your poison of choice is Heartbeat and you want to make
Apache highly available, you do this:
Apache1         Apache2
  |               |
  +---Heartbeat---+
  |               |
DomU1           DomU2
virtual         virtual
machine         machine
  |               |
Xen1            Xen2
kernel          kernel
  |               |
Node1           Node2
hardware        hardware

A real cluster would look like this:
Apache1         Apache2
  |               |
  +---Heartbeat---+
  |               |
Node1           Node2
hardware        hardware


Very little difference.

Hope that helps!

CD

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