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Re: [Xen-devel] will this clever plan work?

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Subject: Re: [Xen-devel] will this clever plan work?
From: "Mark A. Williamson" <mark.williamson@xxxxxxxxxxxx>
Date: Thu, 11 Nov 2004 16:19:24 +0000
Cc: "Eric S. Johansson" <esj@xxxxxxxxxx>
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> I thought of two applications for Xen that could be amusing.  First is
> as a base for a firewall.  The idea would be that in order to upgrade to
> the next release of the firewall, you would create a new virtual machine
> image and disable (but not necessarily expire) the previous version.

It should be possible to build something like that on top of Xen.  It'd be 
quite cute too ;-)

> Ideally these would be complete system images that one could just add to
> and replace as necessary.  I do hope it's also possible for a linux
> system to change the xen configuration so it could boot to the new
> configuration.

One nice way to set this up would be:
* admin software in dom0 (accessed via console or dedicated NIC)
* a separate domain for the firewall software, controlling the NICs directly
* when you upgrade, kill the old domain and build a new one (this can be 
scripted and should be a very quick process with minimal downtime)

> My fantasy is that I will be able to build a single disk image for all
> of the basic OS and application to be shared between multiple virtual
> machines.  Update that single core image using Gentoo magic and be able
> to have separate partitions holding my application data.

Yes, you should be able to do that.  If you're using VBDs (not NFS), the 
standard caveats for shared data apply:
* domains can't write to the shared data
* you can't update the shared data while the domains are running (otherwise 
you'll confuse them)


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