Use iRules to query number of active connections against a node

If I may add, it doesn't sound like you need to worry about load balancing algorithms, although this can be done with the LB::mode command. If you're doing a DNS resolution on each HTTP request, then the returned value is presumably going to be a single IP address. To Patrik's point though, this can be expensive. It might make more sense to manage a local table entry and cache a response for at least as long as the TTL in the response. If the table entry exists, use it, otherwise query and insert the value into the table for later use.

I suppose it's possible, but do the returned IP addresses change wildly? If not, it may also make sense to just automate the update of the pool members using a perpetual script, and subsequently monitor these members in case an IP goes away between script calls.