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From Jess Holle <>
Subject Re: mod_proxy / mod_proxy_balancer
Date Wed, 06 May 2009 13:07:27 GMT
jean-frederic clere wrote:
>> Should general support for a query URL be provided in 
>> mod_proxy_balancer?  Or should this be left to mod_cluster?
> Can you explain more? I don't get the question.
What I mean is

   1. Should mod_proxy_balancer be extended to provide a balancer
      algorithm in which one specifies a backend URL that will provide a
      single numeric health metric, throttle the number of such requests
      via a time-to-live associated with this information, and balance
      on this basis or
   2. Should mod_cluster handle this issue?
   3. Or both?
          * For instance, mod_cluster might leverage special nuances in
            AJP, JBoss, and Tomcat, whereas mod_proxy_balancer might
            provide more generic support for helath checks on any back
            end server that can expose a health metric URL.

 From your response below, it sounds like you're saying it's #2, which 
is /largely /fine and good -- but this raises questions:

   1. How general is the health check metric in mod_cluster?
          * I only care about Tomcat backends myself, but control over
            the metric would be good.
   2. Does this require special JBoss nuggets in Tomcat?
          * I'd hope not, i.e. that this is a simple matter of a
            pre-designated URL or a very simple standalone socket protocol.
   3. When will mod_cluster support health metric based balancing of Tomcat?
   4. How "disruptive" to an existing configuration using
      mod_proxy_balancer/mod_proxy_ajp is mod_cluster?
          * How much needs to be changed?
   5. How portable is the mod_cluster code?
          * Does it build on Windows?  HPUX?  AIX?

I say this is largely fine and good as I'd like to see just the 
health-metric based balancing algorithm in Apache 2.2.x itself.
>> Does mod_cluster provide yet another approach top to bottom (separate 
>> than mod_jk and mod_proxy/mod_proxy_ajp)?
> Mod_cluster is just a balancer for mod_proxy but due to the dynamic 
> creation of balancers and workers it can't get in the httpd-trunk code 
> right now.
>>  It would seem nice to me if mod_jk and/or mod_proxy_balancer could 
>> do health checks, but you have to draw the line somewhere on growing 
>> any given module and if mod_jk and mod_proxy_balancer are not going 
>> in that direction at some point mod_cluster may be in my future. 
Jess Holle

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