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From jean-frederic clere <>
Subject Re: mod_proxy / mod_proxy_balancer
Date Wed, 06 May 2009 15:26:57 GMT
Jess Holle wrote:
> 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?

Please ask the mod_cluster questions in the list. I will answer there.



> 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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