[Nottingham] DNS question for specifying redundant servers

[Joshua Lock]

On Thu, 2008-04-03 at 21:35 +0100, Martin wrote:
> >From discussions last night...
> 
> 
> OK, so how is this done in general?...
> 
> You have multiple servers dotted around the country/world with different
> internet addresses. So how do you set the DNS for the world such that
> normally only one server takes all the load but one of the others picks
> up all the load if the first should fail? And thence, the third picks up
> the load if the second should fail?
> 
> Or is this never done this way?
> 
> If you have the DNS give (round-robin?) multiple addressing for the
> three servers, what happens if one or two fail in that case?
> 
> Answers for mail servers and web servers please...

This sort of thing is done all the time, I recently read something
interesting about how Last.fm solve a similar problem for their
memcached servers. With a hashing algorithm of course!

http://www.last.fm/user/RJ/journal/2007/04/10/392555/
http://www.spiteful.com/2008/03/17/programmers-toolbox-part-3-consistent-hashing/

Interesting reading, may not directly answer your question but I thought
I'd share it. :)

- J
-- 
Joshua Lock <incandescant at gmail.com>