Failover

[Sam Wilson]

In article <gt3l6f$17m9$1 at sf1.isc.org>, <Philippe.Simonet at swisscom.com> 
wrote:

> This is not the DNS job to check at the web service availability.
> You could make an external script that is testing for the service availibil=
> ity
> and change the dns accordingly, like (...) :
> 
> web1 active  ?
>     yes : was it active at last test ?
>             yes : do nothing
>             no : set www to point to web1 in DNS
>     no : was it already inactive ?
>             yes : do nothing
>             no : set www to point to web2 in DNS
> 
> and with having www/web1/web2 having a low TTL.

We do something like this for some not-very-critical services.  A script 
(happens to run on a nameserver, but that's coincidental) watchdogs a 
number of servers and uses (suitably secured) dynamic update to remove 
non-responsive ones from a low-TTL roundrobin.  It knows not to remove 
the last entry.

Sam