This sort of behavior is called names like "high availability" or "failure
roll-over". As you note, when the primary host is not operating, it cannot
refer surfers to the second. So this is not a solution you can implement
on the primary host. It has to be implemented "earlier" in the process or
on a second machine.
What you need is the second server to assume the primary server's IP
address. There are packages like 'heartbeat' and ... blocking on the name,
something like 'fake'... that are designed to help build this solution. If
you search for 'high available linux' you should find some literature on this.
Or you need some DNS magic. With the way DNS works (it caches data) you
cannot change DNS info on a dime and I'm not sure how you would have a
machine far away assume the IP unless both machines are in the same IP
space (e.g., connected by a WAN). If they are served by different DNS
servers, I don't think this would work. Anyway, you would have to control
your DNS server in order for this to work. And don't go to great lengths
to make your web server redundant and then have a single DNS host become
the SPOF, you'll need a roll-over plan for it as well.
And if your site records data, you may need a way to make this data
available on redundant servers. Coda is the name of a file system which is
supposed to be able to do this (maintain synchronized data across several
file servers) although I've never met anyone running it to ask them how
well it actually works.
You can also buy clustering solutions from Red Hat (or does this come with
one of their products?), Turbo Linux, etc. These would solve much the same
problem you are describing and add a performance boost as well.
I think these are are fairly deep waters.
-Alan
At 10:07 PM 11/9/00 , Ted Hilts wrote:
>This is all fine except when the primary hosted web site dies. Now no
>browser can get to the unadvertised alternative domain name because it
>is not known. So this is the dilemna. How does the alternative hosted
>web site make itself look like the primarly hosted web site when the
>primary web site is down?
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