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From jean-frederic clere <jfcl...@gmail.com>
Subject Re: mod_proxy / mod_proxy_balancer
Date Wed, 06 May 2009 12:29:19 GMT
Jess Holle wrote:
> jean-frederic clere wrote:
>> Jess Holle wrote:
>>> An ability to balance based on new sessions with an idle time out on 
>>> such sessions would be close enough to reality in cases where 
>>> sessions expire rather than being explicitly invalidated (e.g. by a 
>>> logout).
>> Storing the sessionid to share the load depending on the number of 
>> active sessions, brings a problem of security, no?
> To the degree that you consider Apache vulnerable to attack to retrieve 
> these, yes.
> 
> I prefer the health check request approach below for this and other 
> reasons (amount of required bookkeeping, etc).
>>> Of course that redoes what a servlet engine would be doing and does 
>>> so with lower fidelity.  An ability to ask a backend for its current 
>>> session count and load balance new requests on that basis would be 
>>> really helpful.  Whether this ability is buried into AJP, for 
>>> instance, or is simply a separate request to a designated URL is 
>>> another question, but the latter approach seems fairly general and 
>>> the number of such requests could be throttled by a time-to-live 
>>> setting on the last such count obtained.
>>>
>>> Actually this could and should be generalized beyond active sessions 
>>> to a back-end health metric.  Each backend could compute and respond 
>>> with a relative measure of busyness/health and respond and the load 
>>> balancer could then balance new (session-less) requests to the least 
>>> busy / most healthy backend.  This would seem to be *huge* step 
>>> forward in load balancing capability/fidelity.
>>>
>>> It's my understanding that mod_cluster is pursuing just this sort of 
>>> thing to some degree -- but currently only works for JBoss backends.
>> This wrong it works with Tomcat too.
> mod_cluster works with Tomcat, but according to the docs I've seen the 
> dynamic (health/session metric based rather than static) load balancing 
> only worked with JBoss backends.
> 
> Or has this changed?

No it is still like that but the singleton logic used in JBossAS 
requires a JBoss clustering logic but it should be available in the next 
version.

Cheers

Jean-Frederic

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