Pool Definition

Ranvir,

I'm not exactly sure what are you looking for but maybe the very basic

layer 4 loadbalancing can do trick for your. If you configure your BIG-IP like this:

pool dev_servers {
   member b.my.com:9999
   member c.my.com:9998
}
virtual a.my.com:80 {
   use pool dev_servers
}

any URI starting with http://a.my.com/ will be loadbalanced to one of the two servers. BIG-IP performs destination address and port translation as a side-effect of loadbalancing (unless you turn it off in configuration), so for example URI http://a.my.com/dev will be effectively translated to http://b.my.com:9999/dev.

If you want to loadbalance only some URIs you can use iRules to do the filtering. For example if only URIs starting with http://a.my.com/dev/ should be loadbalanced to servers b.my.com and c.my.com and all other URIs should be served by server www.my.com, you can use following configuration:

pool dev_servers {
   member b.my.com:9999
   member c.my.com:9998
}
pool default {
   member www.my.com:80
}
rule dev_filter {
   if(http_uri starts_with "/dev/") {
      use pool dev_servers
   } else {
      use pool default
   }
}
virtual a.my.com:80 {
   use rule dev_filter
}

So, to (finally) answer your question: there is no way how to associate pool members with URIs at the pool level, but you can achieve the same using iRules.