replication

[tech@bishop.dhs.org]

As a favor to a friend, I'm trying to setup a mirror of his server,
where I can basically be a 'hotswap' for him.  So far, the main problem
that I'm running into is that everything is ip-based.  For instance,
it's dead-simple to be a secondary dns server for him, but if his box
(which hosts dns, web, and mail) goes down, then I'm simply pointing 
people into dead-space, right?  Well, email is the one standout, where
the MX records would get them to my machine, but I'm having a hard time
figuring out how to make web and dns do the same thing.

To explain what I mean, say he's box a, ip 10.0.0.1, i'm b, ip
192.168.0.1.  We are on completely different networks, with different
providers.  So his machine/connection goes down, and I, using mon or bb,
detect it.  Now what?  bind happily tells people to go to 10.0.0.1 for
foo.org.  My carefully mirrored httpd.conf contains a bunch of lines
talking about <VirtualHost 10.0.0.1:80>.  Without manually editing all
those, what's the solution?  And, just to make things doubly difficult,
it would be really, really nice if it worked as both a 'normal'
secondary, and a mirror, at the same time. :-P  But if I had to choose,
it'd definetly be to be a mirror.

Pointers to the FM to R would be appreciated, google just got me a bunch
of links about mirroring with hot-swappable computers on the same
network, or setting up secondary dns servers, neither of which as
particularly helpful :-)

Thanks!

D.A.Bishop

P.S.  The most helpful thing is that we are running matching version of
debian, so software installing/version matching is no problem at all...