iRule Source IP to prioritized list of pool members

Basically, you are forcing the load balancing to member 1 whatever its status is. You need to either check its status before selecting it, or to use LB_FAILED event after selection to reselect another pool member.

    when CLIENT_ACCEPTED {
     if { [IP::addr [IP::client_addr] equals a.a.a.a%12] } {
      if { [LB::status pool test_pool member 2.2.2.2%12 8443] eq "up" } {
       pool test_pool member 2.2.2.2%12 8443
      } else {
       pool test_pool member 3.3.3.3%12 8443
      }
     }
    }