@Nullable protected InetAddress getSelectedHostString(SocketAddress addr) {
        if (addr instanceof InetSocketAddress) {
            return ((InetSocketAddress) addr).getAddress();
        } else {
            // If it's some other kind of address, just set it to empty
            return null;
        }
    }
function to run when a connection is acquired before returning it to caller.
zuul-core/src/main/java/com/netflix/zuul/netty/connectionpool/PerServerConnectionPool.java