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From "Akins, Brian" <>
Subject Re: ping for http in mod_proxy
Date Thu, 14 Feb 2008 11:49:26 GMT
On 2/14/08 6:44 AM, "Plüm, Rüdiger, VF-Group" <>

> 1. We currently have no mechanism in place that "simulates" these kind of
>    failures we experience ourselves with the backend for the client. Returning
>    a 500 or 503 does not cause the client to repeat the request. IMHO we would
>    need to cut off the network connection without sending anything to trigger
>    this behaviour in a well designed client.

Hrm.. Seems like the HTTP client should "just handle" this case.

> 2. Clients are only allowed to resend the request automatically, if the
> request
>    was idempotent. Clients are not allowed to do so with non-idempotent
> requests
>    like POST's without user intervention. So by probing the keepalive
> connection
>    before sending the request we want to reduce these cases.

>From real world experience, I can say that we have rarely every had an issue
with POSTS.  The active health-checking we do is based on how our load
balancers do it.  They (the load balancers) can occasionally send requests
to a down server for a few seconds if it goes down in between healthchecks.
Sound bad in theory, but in reality, it has never been a real issue.

Brian Akins
Chief Operations Engineer
Turner Digital Media Technologies

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