Irule to Load Balance traffic based on group of IP's

There are a few ways to deal with this, but one example is to use an iRule data group and match the specific source IP and make a decision based on that. I would set this up using two pools, a data group and a rule as per this example:

Pool1 - Server 1 and 2 Pool2 - Server 3

iRule Data group (String type)

iRule to direct the traffic:

when HTTP_REQUEST {
    if {[class match [IP::client_addr] equals Pool1IPs} {
        Pool Pool1
    } else {
        Pool Pool2
    }
}