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From Rainer Jung <rainer.j...@kippdata.de>
Subject Re: [users@httpd] Sticky Session with no control on origin server cookies
Date Thu, 26 Aug 2010 10:13:02 GMT
On 26.08.2010 11:57, michael bienstein wrote:
> Hi all. I'm trying to configure a proxy_loadbalancer with sticky
> session. I read around the web and in the source code and discovered
> that this module expects to handle sticky session by re-using the user's
> session ID provided by the origin server. This is different to BigIP
> which injects its own cookie that it keeps track of. Apache also expects
> the origin server to know it is being load-balanced and to change the
> session ID it creates to include a "route" that identifies that origin
> server.
>
> So for example if my origin server is Tomcat then the session cookie
> would be JSESSIONID=12345... and Tomcat has to be modified to make it
> JSESSIONID="12345.route1". Apache mod_proxy_loadbalancer sees this and
> finds the route1 and chooses the right origin server based on that. I
> also read that PHP doesn't have the possibility of changing the cookie,
> but since PHP runs typically on Apache, it is possible to modify the
> configuration of the origin server to post-process the request to add it.
>
> My problem is that I load balance a custom web server and/or IIS and we
> have neither of these options available. I need the cookie to go through
> as originally created and I can't change the way it gets created. So,
> how to do it?
>
> I have tried to add a cookie at the proxy server, but I can't get this
> to only happen when the origin server sends through its cookie. In fact
> if the origin server sends an error code, the environment variable I use
> with SetEnvIf isn't set correctly. I can't see how to add a cookie in a
> post-processing filter of some sort either. The only ways I see to add
> cookies are in mod_rewrite (which seems strange to me) and via mod_headers.
>
> Any ideas?

Have a look at the second example in

http://httpd.apache.org/docs/trunk/mod/mod_proxy_balancer.html#example

It uses the following features:

- Apache itself can also set a cookie
- the value of the cookie can be interpolated from
   Apache environment variables that are being set
   by the balancer
- setting the cookie can be made dependent on
   whether the load balancer set a variable indicating
   that the request changed nodes (or wasn't sticky)

All of the ingredients used in this example for Apache trunk (the actual 
beta version 2.3) should IMHO be already available in 2.2 (except for 
the nice example in the docs).

If you want to track how this works, you can add

%{Set-Cookie}o %{ROUTEID}C %{BALANCER_WORKER_ROUTE}e 
%{BALANCER_ROUTE_CHANGED}e

to your LogFormat (Access-Log).

NOTE: I think the first of these config lines should use "Set-Cookie" 
instead of "Set-Cookie:".

Regards,

Rainer

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