<b>Better way to code iRule in 4.5.x code ???</b>

Regular expressions are the least efficient way of matching in

iRules (especially in v4.x). The regex version of the rule is very likely going to be measurably slower than the if-then chain. The most efficient way to match an item of a set in an iRules is to use classes. Like this:

class apache_sites {
   "site1"
   "site2"
   "site3"
   "site4"
   "site5"
   "site6"
   "site7"
}
rule match_apache_sites {
   if( http_uri contains one of apache_sites) {
       use pool APACHE_POOL
   } else {
       use pool IISWEB-POOL
   }
}

NOTE: the above rule matches also URIs containing the items of the class as substring (e.g. "site666" or "parasite1"). If those matches are not desired, you need to either add delimiting characters to the items in the set (e.g. "/site1/"), use other match operator (e.g. "starts_with", "equals" or "ends_with) or use the substr function to extract the portion of the URI to be matched.

FYI, the tolower function is available only in 4.6.x.