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From Jess Holle <>
Subject Re: mod_proxy_balancer issue
Date Thu, 28 Aug 2008 13:57:30 GMT
Jess Holle wrote:
> Agreed, but this is concerning *both* mod_jk and mod_proxy and I've 
> been scolded for cross posting...
> At the core, I'm looking for 2 things:
>    1. Something to limit the maximum impact of having many dead
>       workers under a load balancer on normal requests
>           * Assuming there are live workers available, of course, i.e.
>             the process of discovering that dead workers are still
>             dead shouldn't overtly impact any normal request.
>           * Sample situation: load balancing over 9 ports, many of
>             which do not have an active Tomcat associated at the
>             time.  If there is only one Tomcat alive every 'retry'
>             seconds (in the mod_proxy case, same thing, but different
>             parameters for mod_jk), a normal request is delayed by a
>             period of 8*dead-connection-latency.  That's neither
>             necessary nor acceptable.
>           * Possible solutions include having a background thread ping
>             the health of workers rather than allowing normal requests
>             to do so or limiting the number of workers any normal
>             request will attempt to recover.
Clearly if we take the approach of a backgroung ping solution, it would 
be ideal to use cping rather than any sort of real request.
>    1. Something to reduce the severity of log messages when
>       discovering that a dead worker is still dead.
>           * There is no need to fill the error logs with notices that
>             a worker that has been dead is still dead.  This is good
>             troubleshooting info and should be logged, but at a lower
>             severity level that does not show up in the logs by default.
>           * Depending on the solution to (1), this might just fall out
>             of that.
> If you believe we should start up a discussion on httpd dev as to how 
> to solve these issues at this point that sounds great to me -- though 
> we also need to solve them in mod_jk (as our current plan is to use 
> mod_proxy_ajp for Apache 2.2 and we have no alternative but the 
> jk/isapi connector for IIS).
Also to be clear I need solutions to these problems one way or another, 
so if nothing else I'll have to hack in something into our own fork of 
the code.

I have a fair amount of time to solve these problems, however, so I'd 
much rather see them solved in a good, general way that can be a 
value-add part of mod_jk and mod_proxy -- rather than a one-off fork.

Jess Holle

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