F5 Reverse Proxy setup

Hi kashif_shahzad , 
please try this : 

when HTTP_REQUEST { 
 if {[HTTP::host] eq "exampel.com"}{ 
  pool pool_1
 } elseif {[HTTP::host] eq "site1.com"}{ 
     pool pool_2
}
}

> Make sure with pools names within irule as it must be identical with pool name itself , usually I copy pool name and paste it within irule to make sure the names are identical. 

> We can do your request by anothe approache , Do you know about Local traffic policy , it is a very useful tool in f5 and can replace iRule in many implementations but not all as irule used in more complex approaches. 
> if you need me to implement your request by Local traffic policy instead of irules , I’d love to do that definitly. 

I hope this helps you. 
regards