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From Plüm, Rüdiger, VF-Group <>
Subject Re: ping for http in mod_proxy
Date Wed, 13 Feb 2008 17:41:59 GMT

> -----Ursprüngliche Nachricht-----
> Von: Akins, Brian 
> Gesendet: Mittwoch, 13. Februar 2008 18:34
> An:
> Betreff: Re: ping for http in mod_proxy
> On 2/13/08 12:27 PM, "Plüm, Rüdiger, VF-Group" 
> <>
> wrote:
> > This does not help with race conditions on HTTP keepalive 
> connections.
> > Nevertheless active healthchecking could be useful. But on 
> a busy site
> > I guess a real request will notice before the healthcheck 
> that one backend
> > is down or the frequence of health checks needs to be insane.
> On a busy site you want to know if a server is down before 
> you send a few
> thousand requests to it and want to know that it's up as soon as it's
> available so you can send a few thousand requests to it.

Agreed, but I doubt that it is possible with a reasonable amout of health
check frequency to find out before the first real request falls through,
provided that your health checks are designed to only fail if the backend
is down. If your health checks are smarter and notice that the backend will
fail soon (e.g. because it reached 98% or 99% percent of its capacity) then
this is a different story and can be very useful.
Regarding the reactivation of a failed backend I fully agree: Active health
checks would be an asset here instead of just retrying failed backends periodically
with real requests.



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