A program which can monitor HTTP service and change DNS record on fail?

[Kevin Darcy]

Jakob Bak wrote:

> Does anybody recommend any solution/application which will allow our Red Hat
> dns to change a zone record to pointing at another HTTP server (IP) if the
> ordinary HTTP server is down?

There's no good way to use DNS for webserver failover. A *bad* way is to have a
script monitor the health of the primary webserver periodically and change the
A record if it goes down (possibly using Dynamic Update to make the change
quickly and cleanly). The downside of this is that in order for the change to
be seen quickly by other nameservers and thus clients, you need to reduce your
TTL (Time-to-Live) values to ridiculously low values, which increases the load
on your nameservers, and is basically a rather anti-social thing to do since it
also increases the load on everyone *else*'s nameservers too. Yuck.

For this reason, folks who are serious about webserver load-balancing usually
go for a clustering solution, or buy a device like the ones Cisco sells, which
can "frontend" multiple web servers behind a single IP address.


- Kevin