On Thu, Aug 24, 2006 at 12:00:10PM -0700, ben wrote:
> I just spent more time than I would have liked to searching for info
> on providing HA/LB via CARP (and possibly other tools) for individual
> services (such as http) rather than IP addresses. I was surprised to
> find just about nothing on the topic since it seems like something
> people would want to use CARP for.
>
> For example, lets say I have two machines set up as web servers,
> sharing an IP address and load balanced with CARP. The httpd on one
> host dies but it's interface is fine.
>
> Doesn't that mean CARP has no effect and approximately half the
> requests going to the virtual host ip address will timeout? That
> sucks.

Yes, that would be the result.

> I'm guessing you can configure ifstated to run curl or something every
> few seconds to monitor the httpd and respond by taking the CARP
> interface down or rig up some hoc shell script to do roughly the same
> thing. Right?

Well, you wouldn't ordinarily use ifstated(8) for that - it's meant to
respond to changes in the interface, not initiate them - but that's
essentially correct.

> Seems like someone, somewhere must have thought about doing this with
> airline food before. Am I right folks??

I'm afraid I don't catch the airline food, but there certainly are
scripts around. Some were posted here, IIRC.

Note that application-level proxies, while much more heavyweight, do
have something of a place here.

Joachim