custom sorry server redirection

I'm interested in creating an irule that would redirect login requests to a 'sorry' server in the event a certain threshold is reached. The twist here is that I'm not looking for an irule that would kick in on LB::Fail but when the number of apache processes reaches a certain level on a web server (say 100 concurrent), redirect login requests (and only login requests) to a "sorry" server until requests fall under that threshold.

 

I believe setting up the redirection is fairly straightforward but the thing I'm having trouble with is monitoring my web servers so that when they reach that threshold, then the remaining irule actions could get kicked off.

 

I was hoping that I could simply poll the pool member "current connections" statistics because the value of current connections in the pool matches the number of apache processes executing on the web servers at that particular point in time. However, I can't find a function in the irule documentation that would provide this.

 

Has anyone had any luck integrating irules in this manner who could point me in the right direction or am I looking at something that is more of an application of icontrol?