From Leo's mailbag:
> From: A Computer User
> Sent: June 15, 2008
> To: Ask Leo!
> Subject: IP based failover?
>
> Leo,
> If I host web sites at my office using IIS 6, have a static IP, and
> point the DNS to that IP, the name resolves very well. My question,
> is:
>
> How can I set up my web servers, so that in the event my office server
> goes down or is powered off, a person seeking my web pages will be
> redirected to another server at another location halfway across the
> country, that contains a similar copy of my webs?
>
> Is it possible to just add a second DNS entry, and if the first one is
> not found then it will automatically go to the second DNS which points
> to the other server at the other location? What is the best way to
> accomlish this?
Short answer: no.
Longer answer: an IP address - particularly a static one - points
to a *machine*. If that machine is not up, then there is no defined
way to try "somewhere else" - that's simply not built into the
way that the internet protocols work.
The way large corporations handle this is that the IP address
points to a device which is a load balancer - and it has the smarts
to know when one the machines it's "in font of" are off line. It
tends to be a pricy bit of equipment.
Surprisingly you CAN define more than one IP address for a domain name,
but the IP addresses are handed out at random. Which means that if you
assign two different IP addresses, the one half of all requests will
go to one machine, and the other half to the other. And if either one is
down then one half of connection attempts will fail. Again, there's no
automatic fail-over built into those steps.
Sorry.
--
Thanks for asking,
Leo Notenboom
Article 1751
| Category:
Internet
