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Re: [Xen-devel] Pointers needed

Hi Jan,

I just ran across this while skimming through old xen-devel messages.
Did you ever get answers?  It looks like the thread got dropped.  

Your problem is similar to some I've been thinking of applying Xen to.
Some things that might be applicable:

- Use NFS root partitions.  Xen can serve these from domain0 with good
  isolation between hosts.  The NFS packets never need hit the real wire.

- Use read-only /usr partitions to store invariant bits. 

- Use conventional HA techniques (shared SCSI or FC, etc.) to migrate
  physical disks between hosts on failover.

- Sometimes you still need to patch 80 hosts.  See infrastructures.org.

The in-development copy-on-write Xen virtual block devices will help a
great deal with this sort of deployment.

Anyone else see any better ways to do this?


On Fri, Nov 28, 2003 at 05:22:52PM +0200, Jan van Rensburg wrote:
> Hi,
> We're going to start a project soon for a fairly big client. Part of 
> the project involves setting up a highly available web cluster with 
> load balancing, based on RedHat enterprise linux 3, that will run about 
> 80 virtual web servers. One of the requirements of the web server setup 
> is QOS guarantees for the virtual web sites, so that one virtual host 
> with runaway perl/php etc web pages won't let the whole machine grind 
> to a halt. At first we thought this could be done with Apache, but 
> after careful investigation it does not look like you can have resource 
> guarantees and isolation between virtual web servers. In fact it looks 
> like the only web server really capable of this at the moment is the 
> Zeus range of products. However, we don't want to go that route. 
> Instead we want to run each virtual web server on a separate virtual 
> machine, based on Xen. I would like some pointers about how this might 
> be implemented. First of all, how would you do high availability and 
> load balancing with Xen virtual servers? Secondly, since the different 
> virtual host images are all mostly the same, except for a few minor 
> details, is there a way to have a master image that all the server 
> could boot from, even though each virtual server has it's own IP 
> address and apache config? I don't want to have 80 separate images 
> lying around if they're 99% the same. Neither do I want to patch 80 
> servers separately if a security patch become available.
> I must admit I haven't tried Xen yet, however I have read the 
> documentation available on the web site. Any other pointers on such a 
> setup would be appreciated.
> Regards,
> Jan van Rensburg
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Stephen G. Traugott  (KG6HDQ)
UNIX/Linux Infrastructure Architect, TerraLuna LLC
http://www.stevegt.com -- http://Infrastructures.Org 

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