iRule for sending traffic to a different pool based on the Hostname.

Hi ashk , 

- you must add a HTTP profile in your bigip to let it able to parse http requests and understand the meaning of hostnames and headers. 
you can use the following syntax but after adding http profile first : 

 
 when HTTP_REQUEST { 
  
     #Check requested host header (set to lowercase) 
    switch [string tolower [HTTP::host]] { 
  
       "www.site1.com" { 
          pool site1_pool 
       } 
       "www.site2.com" { 
          pool site2_pool 
       } 
       default { 
          pool default_pool 
       } 
    } 
 } 
 

- you can use If statement as well. 

- the most efficiecnt one is to use Local traffic policies , it's light weight on system CPU and it's very easy to implement. 

I hope this helps you