Killing TCP connection attached to secondary when primary server is back (in active/passive mode)

This is an iRule I created some time ago to do about what you are asking for. In this example pool member 10.0.0.1 is de primary pool member and pool member 10.0.0.2 is the backup pool member. This iRule will monitor TCP traffic when there are active connections to the backup member. When there are active connections being send to the bacup server, while the primary pool member is up (again), it will reject the current active connection to the backup pool member.

Note that this iRule has been tested in my lab only.

when CLIENT_DATA {
    if { [LB::status pool pool_name member 10.0.0.1 80] equals "up" } {
        reject
         Disable future events in this or any other iRule on the virtual server
        event disable all
         Exit this event of this iRule immediately
        return
    }

    TCP::release
    TCP::collect 1
}

when SERVER_CONNECTED {
    if { [IP::addr [LB::server addr] equals 10.0.0.2] } {
        clientside { TCP::collect 1 }
    }
}