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Date: Mon, 17 Sep 2007 17:55:53 +0200
From: Rainer Jung <rainer.jung@kippdata.de>
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To: Tomcat Users List <users@tomcat.apache.org>
Subject: Re: With JK 1.2.x using route causes problems with redirect?
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hi Brian,

Brian.Horblit@thomson.com wrote:
> All,
>  
> Good day!
>  
> For a little background, I'm working on implementing "sub-clusters" with
> the new connector. That is, I will cluster my Tomcats in paris to keep
> network traffic/memory usage down. The connector would preferrentially
> fail-over between sub-cluster Tomcat pairs. But if both elements of a
> Tomcat cluster go down, I'd like the connector to fail-over to another
> sub-cluster (with session loss).
>  
> I realize that the connector "Domain" directive was meant for this. My
> reading of the docs, however, would imply that since the jvmRoute is the
> domain (with sticky sessions), the requests going into a domain would be
> load-balanced between domain memembers.

jvmRoute -> worker.xxx.route
domain influences failover decision, as you want it.

> This would in turn imply (for
> those of us who are paranoid), that we'd have to do synchronous session
> replication at the Tomcat level to *ensure* that under heavy load
> sessions would be replicated before  a user is balanced between cluster
> members. This would then, potentially, slow responses to the client
> since sending the response would be delayed until session replication is
> complete. (Perhaps I should try everything to confirm all this since the
> docs are a wee bit vagues...) So, I thought I'd be sneaky and try other
> directives. Hence:

You can set jvmRoute to the worker name (or as you suggest the worker 
route), use session stickyness and relate differrent workers by using 
the same domain name.

The if all workers are up, stickyness will be effective, if a worker 
dies, JK will choose another worker in the same domain, and only if the 
whole domain is dead choose any other worker.

I'm pretty sure, that you can simulate this somehow with "redirect", but 
the domain concept also works, once you increase the domain size. At the 
end both concepts are very similar.

> I am trying to use JK 1.2.25 to access Tomcat 6. I am setting up 4
> servers paired in two different clusters at the Tomcat level. In the
> workers.properties I have:
>  
> - 4 workers: w1,w2,w3,w4
> - All 4 workers are sub-workers of a load balancer called "router"
> - The 4 workers are configured as two "pairs" where the worker pairs
> preferrentially fail-over to each other using the "redirect" directive.
> - In order to prepare for some more exotic configuration, I have used
> the "route" directive to de-couple the worker name from the
> route/jvmRoute which I use for sticky load balancing.
> - The exotic config will be to define multiple load balancers so I can
> switch them out at runtime via the url=>worker mapping file (since one
> can't reload the workers.properties file at runtime, which is a
> bummer!).

You can do "apachectl graceful". Switching via uriworkermap.properties 
should be fine though.

> I have found that the "redirect" directive is not working all the time.
> If w1 and w2 are set to preferentially fail-over to each other, it does
> not always happen. For example, if I kill the Tomcat w1 is pointing to,
> the connector will at times fail-over to the Tomcat w4 is pointing to.
>  
> If I remove the "route" directive from all workers and ensure the worker
> names match the jvmRoute in Tomcat, all is well - I don't get the
> incorrect fail-overs. It seems then the "redirect" pairs always failover
> to each other.
>  
> Note that the problem seems to appear after I do a failover that behaves
> properly once, restart the failed servers, and try another failover
> test.
>  
> Is my config incorrect? Do the "route" and "redirect" directives not
> play well with each other?
>  
> I've tried this on Windoze (see config below) with all Tomcats on my
> desktop. I've also tried in on Linux with the Tomcats on 4 different
> servers. Same behaviour.
>  
> Thanks very much in advance!
>  
> My workers.properties is as follows:
>  
> 
> ### Global worker maintenance interval in seconds
> worker.maintain=30
>  
> ###
> ### The list of all workers
> ### 
> worker.list=router
>  
> ###
> ### The real workers
> ### 
> # Set w1 properties 
> worker.w1.socket_keepalive=1
> worker.w1.socket_timeout=20
> worker.w1.reply_timeout=20000
> worker.w1.retries=2
> worker.w1.connection_pool_timeout=60
> worker.w1.type=ajp13
> worker.w1.host=localhost
> worker.w1.port=8031
> worker.w1.lbfactor=1
> worker.w1.redirect=w2

or better instead of the redirect: worker.w1.domain=tc12

> worker.w1.route=tc1
>  
> # Set w2 properties 
> worker.w2.socket_keepalive=1
> worker.w2.socket_timeout=20
> worker.w2.reply_timeout=20000
> worker.w2.retries=2
> worker.w2.connection_pool_timeout=60
> worker.w2.type=ajp13
> worker.w2.host=localhost
> worker.w2.port=8032
> worker.w2.lbfactor=1
> worker.w2.redirect=w1

or better instead of the redirect: worker.w2.domain=tc12

> worker.w2.route=tc2
>  
> # Set w3 properties 
> worker.w3.socket_keepalive=1
> worker.w3.socket_timeout=20
> worker.w3.reply_timeout=20000
> worker.w3.retries=2
> worker.w3.connection_pool_timeout=60
> worker.w3.type=ajp13
> worker.w3.host=localhost
> worker.w3.port=8033
> worker.w3.lbfactor=1
> worker.w3.redirect=w4

or better instead of the redirect: worker.w3.domain=tc34

> worker.w3.route=tc3
>  
> # Set w4 properties 
> worker.w4.socket_keepalive=1
> worker.w4.socket_timeout=20
> worker.w4.reply_timeout=20000
> worker.w4.retries=2
> worker.w4.connection_pool_timeout=60
> worker.w4.type=ajp13
> worker.w4.host=localhost
> worker.w4.port=8034
> worker.w4.lbfactor=1
> worker.w4.redirect=w3

or better instead of the redirect: worker.w4.domain=tc34

> worker.w4.route=tc4
>  
> # router is a load balancer 
> worker.router.type=lb
> worker.router.balance_workers=w1,w2,w3,w4
> worker.router.sticky_session=True
> worker.router.sticky_session_force=False
> worker.router.method=S
> worker.router.recover_time=30


You can choose other names as domain names, as long as the correct pairs 
share the same name.

> ###
> ### The status worker
> ### 
> worker.list=jkstatus
> worker.jkstatus.type=status
> 
>  
> Brian D. Horblit
> Senior Principal Engineer
> Thomson Healthcare
> 
> (303) 486-6697
> (800) 525-9083 x 6697
> www.thomsonhealthcare.com <http://www.thomsonhealthcare.com/> 
> brian.horblit@thomson.com

Regards,

Rainer

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