iRule to select pool member depending on client source ip address

If you're not offloading SSL with a client SSL profile applied to the VIP, then any HTTP commands and events will be unavailable. Fortunately though, since all of your conditions are IP-based, you could use the CLIENT_ACCEPTED event instead:

when CLIENT_ACCEPTED {     
    if { [class match [IP::client_addr] equals datagroup1] } {        
        pool pool1             
        log local0. "[IP::client_addr] is 1"            
    } elseif { [class match [IP::client_addr] equals datagroup2] } {        
        pool pool2             
        log local0. "[IP::client_addr] is 2"            
    } else {        
         pool pool3              
         log local0. "[IP::client_addr] is 3"
    } 
}