Invoke another loadbalancer url from current loadbalancer url using irule

Let's look at this from the perspective of "flow". Is the cookiegenerator URL what the client is going to for normal application processing (ie. the website), or is it just a service that must be called to get something before going on to the real website? If the latter, does the client have to make multiple requests to this URL to get what it needs, or is it all done in one request? It would appear from your iRule that this is what you're trying to do, and if so, you would normally add a node command to launch the request off to a given IP address somewhere else, and then an HTTP::retry once that response came back so that you could continue on to the real application. The better option, however, is probably a sideband iRule.

client request -> VIP -> sideband to service -> return from sideband ->             website 

Does that sound like what you need it to do?