@Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        if (maxConnections > 0) {
            int currentCount = connections.getAndIncrement();

            if (currentCount + 1 > maxConnections) {
                LOG.warn(
                        "Throttling incoming connection as above configured max connections threshold of {}",
                        maxConnections);
                Channel channel = ctx.channel();
                channel.attr(ATTR_CH_THROTTLED).set(Boolean.TRUE);
                CurrentPassport.fromChannel(channel).add(PassportState.SERVER_CH_THROTTLING);
                channel.close();
                connectionThrottled.increment();
            }
        }

        super.channelActive(ctx);
    }
Closes any incoming new connections if current count is above a configured threshold.

When a connection is throttled, the channel is closed, and then a CONNECTION_THROTTLED_EVENT event is fired
not notify any other interested handlers.
zuul-core/src/main/java/com/netflix/netty/common/throttle/MaxInboundConnectionsHandler.java