Re: [Xen-users] Re: Redundant server setup

[Matthew Wild <M.Wild@xxxxxxxx>]

On Friday 12 May 2006 00:15, Matthew Palmer wrote:
> On Thu, May 11, 2006 at 11:13:48PM +0200, John wrote:
> > Hello all,
> >
> > I would like your advise/opinion on setting up a redundant Xen
> > infrastructure. We have two identical boxes now running xen: vs01 and
> > vs02 - interconnected with a cross cable on eth1.
> >
> > What I would like to realize is my virtual hosts not being dependent on
> > (a) physical hardware and (b) potential Xen failures due to
> > misconfiration anywhere in the machine.
> >
> > All virtual servers are running on vs01 and I plan to rsync
> > the whole /etc/xen directory to vs02 every night. I tried using scp and
> > that worked OK.
> >
> > Would this be a good setup to realize redundancy?
>
> Not particularly.
>
> What you want is drbd syncing your block devices, with heartbeat
> maintaining the "services" of your domUs.  That'll save you from hardware
> failures, and really nasty Xen misconfigurations (of the "I b0rk3d my grub"
> severity).  It won't save you from minor stuff-ups, like giving a domU the
> wrong bridge -- but then again, there's not much that will manage to save
> yourself from yourself like that.
>
What I've been working on is using a separate box to provide the storage for 
the domUs through iSCSI. So at the moment I have two machines set up as dom0s 
and one NAS box using iscsitarget to provide storage. As long as I use 
the /dev/disk/by-id names for the disks, I can run xm migrate --live and 
everything switches over imperceptibly.

All we need now is to use heartbeat to check if domUs or a dom0 has failed and 
start up on the other as appropriate. It would also be useful to consider 
some load-balancing, though that's a longer term thought.

The other thing that I'm thinking hard about is how to decide which domUs come 
up automatically on which dom0, though heartbeat may be able to help with 
that.

Matthew
-- 
Matthew Wild                       Tel.: +44 (0)1235 445173
M.Wild@xxxxxxxx                    URL http://www.ukssdc.ac.uk/
UK Solar System Data Centre and
World Data Centre - Solar-Terrestrial Physics, Chilton
Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, OX11 0QX

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