private static void warnIfInactivePort(
            Server server, int port, @Nullable SessionProtocol protocol) {
        for (ServerPort serverPort : server.activePorts().values()) {
            if ((protocol == null || serverPort.hasProtocol(protocol)) &&
                serverPort.localAddress().getPort() == port) {
                return;
            }
        }
        logger.warn("The specified port number {} does not exist. (expected one of activePorts: {})",
                    port, server.activePorts());
    }
Returns a {@link ZooKeeperUpdatingListenerBuilder} with a ZooKeeper connection string and a znode path.

@param zkConnectionStr the ZooKeeper connection string
@param znodePath the ZooKeeper node to register
@param spec the {@link ZooKeeperRegistrationSpec} to encode and register the {@link Server}
zookeeper3/src/main/java/com/linecorp/armeria/server/zookeeper/ZooKeeperUpdatingListener.java