iRule configuration for sending requests to specific pool members depending on user input

Well, you can replace the pool command with a node command and just point to the IP and port of the server directly:

when HTTP_REQUEST {
   if { [class match... } {
      node 10.1.1.1 80
   } else {
      node 10.1.1.2 80
   }
}

But, that will eventually stop scaling well. The better option is to create 3 separate pools - one for each app/service. That way if you ever need to add resources for a given application, you just add that to the existing pool and load balancing is built in.