Mapping specific requests to a single ZEO client instance

As a follow up to Apache Round Robin for ZeoClients:

we needed to send session specific things to a single instance.

An example of why this is necessary is for collective.captcha. If the connections are being round robin-ed you get audio and image files from different instances. That is BAD. It doesn't work.

First make sure varnish doesn't cache the captcha images and audio or your captcha protected form page.
In varnish.vcl add:

# Do NOT cache captcha image, audio, request
  if (   req.url ~ "/@@captcha"
      || req.url ~ "/contact-info"
     ) {
        pipe;
       }

Next we need to map a server to do our captcha stuff.
In zopeservers.map add the line:

CAPTCHA localhost:6970

I will leave it to you to think of how to creatively balance requests to the other instances. Perhaps remove teh one that does some captcha and other special work from ALL, or maybe add the other instances more than once... OK I didn't leave much, but there are probably smarter ways to do it.

Finally we need to add a rule for mapping captcha requests to the correct instance.
To the appropriate apache.conf (http.conf) add:

RewriteRule ^/(@@captcha/(audio|image)|contact-info)   \
   http://${zopeservers:CAPTCHA}/VirtualHostBase/http/%{SERVER_NAME}:80/msrd/VirtualHostRoot/$1 [L,P]

Don't forget to restart apache and varnish!!

Thanks to Chris Shenton for suggesting the solution.