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From Jens Schleusener <Jens.Schleuse...@t-systems-sfr.com>
Subject Re: [users@httpd] Apache reverse proxy in front of a Windows NLB cluster
Date Mon, 04 Sep 2006 19:31:50 GMT
Hi,

On Mon, 4 Sep 2006, Nick Kew wrote:

> On Monday 04 September 2006 15:59, Jens Schleusener wrote:
> 
> > Any ideas to handle this situation (second network-interface, iptables,
> > additional server hardware or ...) ?
> 
> Erm, I may be missing your point, but why not just do the balancing
> in the proxy itself?

Since the IIS server respectively the CMS system runs on a NLB (Network 
Load Balancing) Cluster and the CMS requires "affinity" meaning - as I 
understand - that a client must send its request always to the same 
cluster member for preserving session state ... and since the NLB system 
is "given" and at least not directly under my control.

If we do the balancing in the proxy itself we must break up the NLB 
cluster in order to can use two single servers and the requested 
"affinity" functionality must be done by the Apache reverse proxy. Ok?

But how? 

1) Something for e.g. like 

 RewriteEngine on
 RewriteCond %{REMOTE_ADDR}  ^[0-9]\.         [OR]
 RewriteCond %{REMOTE_ADDR}  ^[0-9][0-9]\.
 RewriteRule ^(.*)$          http://1.2.3.4$1 [P,L]
 RewriteRule ^(.*)$          http://1.2.3.5$1 [P,L]

(hopefully correct syntax, should arbitrarily send requests from subnets 
0.0.0.0/8 til 99.0.0.0/8 to one backend and from all others to the second 
one) may perhaps work but didn't have the probably existing "failover" 
functionality of the NLB (or we must fo e.g. check the backends and adapt 
the Apache configuration accordingly).

2) Ok, why not let do the work the Apache (2.2.x) "proxy_balancer"-module 
and use a backend URL starting with the "balancer"-scheme? Since I til yet 
didn't find out how to realize the described "affinity".

I found in the current context two interesting parameters ("route" and 
"stickysession") but I don't know how to apply them correctly and how they 
will work exactly. May be the Apache reverse proxy will add an additional 
cookie to store the information which backend server was used for the 
current "session" and use that cookie to serve further requests?

Would that be realized by roughly the following configuration? 

 ProxyPass / balancer://iis stickysession=iis_sessionid nofailover=On
 <Proxy balancer://iis>
   BalancerMember http://1.2.3.4:80 route=1
   BalancerMember http://1.2.3.5:80 route=2
 </Proxy>

Additionally the mapping rules of our reverse proxy are a little bit complex
so we use "mod_rewrite" and many "RewriteRule"s but in the documentation
I didn't find that the "mod_rewrite" module allows the "balancer"-scheme
so we had probaly to use <Location> or <LocationMatch> sections?

Sorry, I am a balancer newbie, so any corrections, hints or even examples?

Greetings

Jens

-- 
Dr. Jens Schleusener            T-Systems Solutions for Research GmbH
Tel: +49 551 709-2493           Bunsenstr.10
Fax: +49 551 709-2169           D-37073 Goettingen
Jens.Schleusener@t-systems.com  http://www.t-systems.com/

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