1. 基础概念

NameServer 是⼀个⾮常简单的 Topic 路由注册中⼼，其⻆⾊类似 Dubbo 中的 zookeeper ，⽀持 Broker 的动态注册与 发现。

RocketMQ 集群⼯作流程：

1、NameServer 启动服务，监听 TCP 端⼝ ， 集群多节点之间⽆任何信息交互，然后等待 Broker、Producer 、 Consumer 连上来；

2、Broker 启动后，每隔 30 秒向所有的 NameServer 发送⼼跳命令 ；

3、NameServer 接收到请求之后，保存路由信息在本地内存⾥ ，将响应结果返给 Broker 服务；

4、Producer 启动之后，会随机的选择⼀个 NameServer ，并从 NameServer 中获取当前发送的 Topic 存在哪些 Broker 上，轮询从队列列表中选择⼀个队列，然后与队列所在的 Broker 建⽴⻓连接从⽽向 Broker 发消息；

5、Consumer 跟 Producer 类似，跟其中⼀台 NameServer 建⽴⻓连接，获取当前订阅 Topic 存在哪些 Broker 上，然 后直接跟 Broker 建⽴连接通道，开始消费消息。

2. Broker发送心跳包

发送心跳包使用的invokeOneway单向通信方式，注意下这里使用了CountDownLatch实现线程同步

1、Broker 会每隔 30 秒向所有的 NameServer 发送⼼跳命令 ；

使⽤ CountDownLatch 实现多线程同步，可以获取发往所有的 NameServer 的⼼跳命令的响应结果。

2、⼼跳命令包含两个部分：请求头和请求体

image-20240504153846290

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public class BrokerOuterAPI {
    private static final InternalLogger log = InternalLoggerFactory.getLogger(LoggerName.BROKER_LOGGER_NAME);
    private final RemotingClient remotingClient;
    private final TopAddressing topAddressing = new TopAddressing(MixAll.getWSAddr());
    private String nameSrvAddr = null;
    private BrokerFixedThreadPoolExecutor brokerOuterExecutor = new BrokerFixedThreadPoolExecutor(4, 10, 1, TimeUnit.MINUTES,
        new ArrayBlockingQueue<Runnable>(32), new ThreadFactoryImpl("brokerOutApi_thread_", true));

    public BrokerOuterAPI(final NettyClientConfig nettyClientConfig) {
        this(nettyClientConfig, null);
    }

    public BrokerOuterAPI(final NettyClientConfig nettyClientConfig, RPCHook rpcHook) {
        this.remotingClient = new NettyRemotingClient(nettyClientConfig);
        this.remotingClient.registerRPCHook(rpcHook);
    }

    public void start() {
        this.remotingClient.start();
    }

    public void shutdown() {
        this.remotingClient.shutdown();
        this.brokerOuterExecutor.shutdown();
    }

    public String fetchNameServerAddr() {
        try {
            String addrs = this.topAddressing.fetchNSAddr();
            if (addrs != null) {
                if (!addrs.equals(this.nameSrvAddr)) {
                    log.info("name server address changed, old: {} new: {}", this.nameSrvAddr, addrs);
                    this.updateNameServerAddressList(addrs);
                    this.nameSrvAddr = addrs;
                    return nameSrvAddr;
                }
            }
        } catch (Exception e) {
            log.error("fetchNameServerAddr Exception", e);
        }
        return nameSrvAddr;
    }

    public void updateNameServerAddressList(final String addrs) {
        List<String> lst = new ArrayList<String>();
        String[] addrArray = addrs.split(";");
        for (String addr : addrArray) {
            lst.add(addr);
        }

        this.remotingClient.updateNameServerAddressList(lst);
    }

    public List<RegisterBrokerResult> registerBrokerAll(
        final String clusterName,
        final String brokerAddr,
        final String brokerName,
        final long brokerId,
        final String haServerAddr,
        final TopicConfigSerializeWrapper topicConfigWrapper,
        final List<String> filterServerList,
        final boolean oneway,
        final int timeoutMills,
        final boolean compressed) {

        final List<RegisterBrokerResult> registerBrokerResultList = new CopyOnWriteArrayList<>();
        List<String> nameServerAddressList = this.remotingClient.getNameServerAddressList();
        if (nameServerAddressList != null && nameServerAddressList.size() > 0) {

            final RegisterBrokerRequestHeader requestHeader = new RegisterBrokerRequestHeader();
            requestHeader.setBrokerAddr(brokerAddr);
            requestHeader.setBrokerId(brokerId);
            requestHeader.setBrokerName(brokerName);
            requestHeader.setClusterName(clusterName);
            requestHeader.setHaServerAddr(haServerAddr);
            requestHeader.setCompressed(compressed);

            RegisterBrokerBody requestBody = new RegisterBrokerBody();
            requestBody.setTopicConfigSerializeWrapper(topicConfigWrapper);
            requestBody.setFilterServerList(filterServerList);
            final byte[] body = requestBody.encode(compressed);
            final int bodyCrc32 = UtilAll.crc32(body);
            requestHeader.setBodyCrc32(bodyCrc32);
            final CountDownLatch countDownLatch = new CountDownLatch(nameServerAddressList.size());
            for (final String namesrvAddr : nameServerAddressList) {
                brokerOuterExecutor.execute(new Runnable() {
                    @Override
                    public void run() {
                        try {
                            RegisterBrokerResult result = registerBroker(namesrvAddr, oneway, timeoutMills, requestHeader, body);
                            if (result != null) {
                                registerBrokerResultList.add(result);
                            }

                            log.info("register broker[{}]to name server {} OK", brokerId, namesrvAddr);
                        } catch (Exception e) {
                            log.warn("registerBroker Exception, {}", namesrvAddr, e);
                        } finally {
                            countDownLatch.countDown();
                        }
                    }
                });
            }

            try {
                countDownLatch.await(timeoutMills, TimeUnit.MILLISECONDS);
            } catch (InterruptedException e) {
            }
        }

        return registerBrokerResultList;
    }

    private RegisterBrokerResult registerBroker(
        final String namesrvAddr,
        final boolean oneway,
        final int timeoutMills,
        final RegisterBrokerRequestHeader requestHeader,
        final byte[] body
    ) throws RemotingCommandException, MQBrokerException, RemotingConnectException, RemotingSendRequestException, RemotingTimeoutException,
        InterruptedException {
        RemotingCommand request = RemotingCommand.createRequestCommand(RequestCode.REGISTER_BROKER, requestHeader);
        request.setBody(body);

        if (oneway) {
            try {
                this.remotingClient.invokeOneway(namesrvAddr, request, timeoutMills);
            } catch (RemotingTooMuchRequestException e) {
                // Ignore
            }
            return null;
        }

        RemotingCommand response = this.remotingClient.invokeSync(namesrvAddr, request, timeoutMills);
        assert response != null;
        switch (response.getCode()) {
            case ResponseCode.SUCCESS: {
                RegisterBrokerResponseHeader responseHeader =
                    (RegisterBrokerResponseHeader) response.decodeCommandCustomHeader(RegisterBrokerResponseHeader.class);
                RegisterBrokerResult result = new RegisterBrokerResult();
                result.setMasterAddr(responseHeader.getMasterAddr());
                result.setHaServerAddr(responseHeader.getHaServerAddr());
                if (response.getBody() != null) {
                    result.setKvTable(KVTable.decode(response.getBody(), KVTable.class));
                }
                return result;
            }
            default:
                break;
        }

        throw new MQBrokerException(response.getCode(), response.getRemark(), requestHeader == null ? null : requestHeader.getBrokerAddr());
    }

    public void unregisterBrokerAll(
        final String clusterName,
        final String brokerAddr,
        final String brokerName,
        final long brokerId
    ) {
        List<String> nameServerAddressList = this.remotingClient.getNameServerAddressList();
        if (nameServerAddressList != null) {
            for (String namesrvAddr : nameServerAddressList) {
                try {
                    this.unregisterBroker(namesrvAddr, clusterName, brokerAddr, brokerName, brokerId);
                    log.info("unregisterBroker OK, NamesrvAddr: {}", namesrvAddr);
                } catch (Exception e) {
                    log.warn("unregisterBroker Exception, {}", namesrvAddr, e);
                }
            }
        }
    }

    public void unregisterBroker(
        final String namesrvAddr,
        final String clusterName,
        final String brokerAddr,
        final String brokerName,
        final long brokerId
    ) throws RemotingConnectException, RemotingSendRequestException, RemotingTimeoutException, InterruptedException, MQBrokerException {
        UnRegisterBrokerRequestHeader requestHeader = new UnRegisterBrokerRequestHeader();
        requestHeader.setBrokerAddr(brokerAddr);
        requestHeader.setBrokerId(brokerId);
        requestHeader.setBrokerName(brokerName);
        requestHeader.setClusterName(clusterName);
        RemotingCommand request = RemotingCommand.createRequestCommand(RequestCode.UNREGISTER_BROKER, requestHeader);

        RemotingCommand response = this.remotingClient.invokeSync(namesrvAddr, request, 3000);
        assert response != null;
        switch (response.getCode()) {
            case ResponseCode.SUCCESS: {
                return;
            }
            default:
                break;
        }

        throw new MQBrokerException(response.getCode(), response.getRemark(), brokerAddr);
    }

    public List<Boolean> needRegister(
        final String clusterName,
        final String brokerAddr,
        final String brokerName,
        final long brokerId,
        final TopicConfigSerializeWrapper topicConfigWrapper,
        final int timeoutMills) {
        final List<Boolean> changedList = new CopyOnWriteArrayList<>();
        List<String> nameServerAddressList = this.remotingClient.getNameServerAddressList();
        if (nameServerAddressList != null && nameServerAddressList.size() > 0) {
            final CountDownLatch countDownLatch = new CountDownLatch(nameServerAddressList.size());
            for (final String namesrvAddr : nameServerAddressList) {
                brokerOuterExecutor.execute(new Runnable() {
                    @Override
                    public void run() {
                        try {
                            QueryDataVersionRequestHeader requestHeader = new QueryDataVersionRequestHeader();
                            requestHeader.setBrokerAddr(brokerAddr);
                            requestHeader.setBrokerId(brokerId);
                            requestHeader.setBrokerName(brokerName);
                            requestHeader.setClusterName(clusterName);
                            RemotingCommand request = RemotingCommand.createRequestCommand(RequestCode.QUERY_DATA_VERSION, requestHeader);
                            request.setBody(topicConfigWrapper.getDataVersion().encode());
                            RemotingCommand response = remotingClient.invokeSync(namesrvAddr, request, timeoutMills);
                            DataVersion nameServerDataVersion = null;
                            Boolean changed = false;
                            switch (response.getCode()) {
                                case ResponseCode.SUCCESS: {
                                    QueryDataVersionResponseHeader queryDataVersionResponseHeader =
                                        (QueryDataVersionResponseHeader) response.decodeCommandCustomHeader(QueryDataVersionResponseHeader.class);
                                    changed = queryDataVersionResponseHeader.getChanged();
                                    byte[] body = response.getBody();
                                    if (body != null) {
                                        nameServerDataVersion = DataVersion.decode(body, DataVersion.class);
                                        if (!topicConfigWrapper.getDataVersion().equals(nameServerDataVersion)) {
                                            changed = true;
                                        }
                                    }
                                    if (changed == null || changed) {
                                        changedList.add(Boolean.TRUE);
                                    }
                                }
                                default:
                                    break;
                            }
                            log.warn("Query data version from name server {} OK,changed {}, broker {},name server {}", namesrvAddr, changed, topicConfigWrapper.getDataVersion(), nameServerDataVersion == null ? "" : nameServerDataVersion);
                        } catch (Exception e) {
                            changedList.add(Boolean.TRUE);
                            log.error("Query data version from name server {}  Exception, {}", namesrvAddr, e);
                        } finally {
                            countDownLatch.countDown();
                        }
                    }
                });

            }
            try {
                countDownLatch.await(timeoutMills, TimeUnit.MILLISECONDS);
            } catch (InterruptedException e) {
                log.error("query dataversion from nameserver countDownLatch await Exception", e);
            }
        }
        return changedList;
    }

    public TopicConfigSerializeWrapper getAllTopicConfig(
        final String addr) throws RemotingConnectException, RemotingSendRequestException,
        RemotingTimeoutException, InterruptedException, MQBrokerException {
        RemotingCommand request = RemotingCommand.createRequestCommand(RequestCode.GET_ALL_TOPIC_CONFIG, null);

        RemotingCommand response = this.remotingClient.invokeSync(MixAll.brokerVIPChannel(true, addr), request, 3000);
        assert response != null;
        switch (response.getCode()) {
            case ResponseCode.SUCCESS: {
                return TopicConfigSerializeWrapper.decode(response.getBody(), TopicConfigSerializeWrapper.class);
            }
            default:
                break;
        }

        throw new MQBrokerException(response.getCode(), response.getRemark(), addr);
    }

    public ConsumerOffsetSerializeWrapper getAllConsumerOffset(
        final String addr) throws InterruptedException, RemotingTimeoutException,
        RemotingSendRequestException, RemotingConnectException, MQBrokerException {
        RemotingCommand request = RemotingCommand.createRequestCommand(RequestCode.GET_ALL_CONSUMER_OFFSET, null);
        RemotingCommand response = this.remotingClient.invokeSync(addr, request, 3000);
        assert response != null;
        switch (response.getCode()) {
            case ResponseCode.SUCCESS: {
                return ConsumerOffsetSerializeWrapper.decode(response.getBody(), ConsumerOffsetSerializeWrapper.class);
            }
            default:
                break;
        }

        throw new MQBrokerException(response.getCode(), response.getRemark(), addr);
    }

    public String getAllDelayOffset(
        final String addr) throws InterruptedException, RemotingTimeoutException, RemotingSendRequestException,
        RemotingConnectException, MQBrokerException, UnsupportedEncodingException {
        RemotingCommand request = RemotingCommand.createRequestCommand(RequestCode.GET_ALL_DELAY_OFFSET, null);
        RemotingCommand response = this.remotingClient.invokeSync(addr, request, 3000);
        assert response != null;
        switch (response.getCode()) {
            case ResponseCode.SUCCESS: {
                return new String(response.getBody(), MixAll.DEFAULT_CHARSET);
            }
            default:
                break;
        }

        throw new MQBrokerException(response.getCode(), response.getRemark(), addr);
    }

    public SubscriptionGroupWrapper getAllSubscriptionGroupConfig(
        final String addr) throws InterruptedException, RemotingTimeoutException,
        RemotingSendRequestException, RemotingConnectException, MQBrokerException {
        RemotingCommand request = RemotingCommand.createRequestCommand(RequestCode.GET_ALL_SUBSCRIPTIONGROUP_CONFIG, null);
        RemotingCommand response = this.remotingClient.invokeSync(addr, request, 3000);
        assert response != null;
        switch (response.getCode()) {
            case ResponseCode.SUCCESS: {
                return SubscriptionGroupWrapper.decode(response.getBody(), SubscriptionGroupWrapper.class);
            }
            default:
                break;
        }

        throw new MQBrokerException(response.getCode(), response.getRemark(), addr);
    }

    public void registerRPCHook(RPCHook rpcHook) {
        remotingClient.registerRPCHook(rpcHook);
    }
}

3. NameServer维护路由

NameServer 在接收到 Broker 发送的⼼跳请求之后，通过默认的处理器来处理请求，保存路由信息成功后，注册成功状 态返回给 Broker 服务。

源码中，我们可以看到路由信息保存在 HashMap 中 

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public class RouteInfoManager {
    private static final InternalLogger log = InternalLoggerFactory.getLogger(LoggerName.NAMESRV_LOGGER_NAME);
    private final static long BROKER_CHANNEL_EXPIRED_TIME = 1000 * 60 * 2;
    private final ReadWriteLock lock = new ReentrantReadWriteLock();
    private final HashMap<String/* topic */, List<QueueData>> topicQueueTable;
    private final HashMap<String/* brokerName */, BrokerData> brokerAddrTable;
    private final HashMap<String/* clusterName */, Set<String/* brokerName */>> clusterAddrTable;
    private final HashMap<String/* brokerAddr */, BrokerLiveInfo> brokerLiveTable;
    private final HashMap<String/* brokerAddr */, List<String>/* Filter Server */> filterServerTable;
    // ··· ···
}

1、topicQueueTable：Topic 消息队列路由信息，包括 topic 所在的 broker 名称，读队列数量，写队列数量，同步标 记等信息，rocketmq 根据 topicQueueTable 的信息进⾏负载均衡消息发送。

2、brokerAddrTable：Broker 节点信息，包括 brokername，所在集群名称，还有主备节点信息。

3、clusterAddrTable：Broker 集群信息，存储了集群中所有的 Brokername。

4、brokerLiveTable：Broker 状态信息，NameServer 每次收到 Broker 的⼼跳包就会更新该信息。

当 Broker 向 NameServer 发送⼼跳包（路由信息），NameServer 需要对 HashMap 进⾏数据更新，但我们都知道 HashMap 并不是线程安全的，⾼并发场景下，容易出现 CPU 100% 问题，所以更新 HashMap 时需要加锁，RocketMQ 使⽤了 JDK 的读写锁 ReentrantReadWriteLock 。

下⾯我们看下路由信息如何更新和读取：

1、写操作：更新路由信息，操作写锁

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public RegisterBrokerResult registerBroker(
    final String clusterName,
    final String brokerAddr,
    final String brokerName,
    final long brokerId,
    final String haServerAddr,
    final TopicConfigSerializeWrapper topicConfigWrapper,
    final List<String> filterServerList,
    final Channel channel) {
    RegisterBrokerResult result = new RegisterBrokerResult();
    try {
        try {
            // 1. 加写锁
            this.lock.writeLock().lockInterruptibly();

            Set<String> brokerNames = this.clusterAddrTable.get(clusterName);
            if (null == brokerNames) {
                brokerNames = new HashSet<String>();
                this.clusterAddrTable.put(clusterName, brokerNames);
            }
            brokerNames.add(brokerName);

            boolean registerFirst = false;

            BrokerData brokerData = this.brokerAddrTable.get(brokerName);
            if (null == brokerData) {
                registerFirst = true;
                brokerData = new BrokerData(clusterName, brokerName, new HashMap<Long, String>());
                this.brokerAddrTable.put(brokerName, brokerData);
            }
            Map<Long, String> brokerAddrsMap = brokerData.getBrokerAddrs();
            //Switch slave to master: first remove <1, IP:PORT> in namesrv, then add <0, IP:PORT>
            //The same IP:PORT must only have one record in brokerAddrTable
            Iterator<Entry<Long, String>> it = brokerAddrsMap.entrySet().iterator();
            while (it.hasNext()) {
                Entry<Long, String> item = it.next();
                if (null != brokerAddr && brokerAddr.equals(item.getValue()) && brokerId != item.getKey()) {
                    it.remove();
                }
            }

            String oldAddr = brokerData.getBrokerAddrs().put(brokerId, brokerAddr);
            registerFirst = registerFirst || (null == oldAddr);

            if (null != topicConfigWrapper
                && MixAll.MASTER_ID == brokerId) {
                if (this.isBrokerTopicConfigChanged(brokerAddr, topicConfigWrapper.getDataVersion())
                    || registerFirst) {
                    ConcurrentMap<String, TopicConfig> tcTable =
                        topicConfigWrapper.getTopicConfigTable();
                    if (tcTable != null) {
                        for (Map.Entry<String, TopicConfig> entry : tcTable.entrySet()) {
                            this.createAndUpdateQueueData(brokerName, entry.getValue());
                        }
                    }
                }
            }

            BrokerLiveInfo prevBrokerLiveInfo = this.brokerLiveTable.put(brokerAddr,
                new BrokerLiveInfo(
                    System.currentTimeMillis(),
                    topicConfigWrapper.getDataVersion(),
                    channel,
                    haServerAddr));
            if (null == prevBrokerLiveInfo) {
                log.info("new broker registered, {} HAServer: {}", brokerAddr, haServerAddr);
            }

            if (filterServerList != null) {
                if (filterServerList.isEmpty()) {
                    this.filterServerTable.remove(brokerAddr);
                } else {
                    this.filterServerTable.put(brokerAddr, filterServerList);
                }
            }

            if (MixAll.MASTER_ID != brokerId) {
                String masterAddr = brokerData.getBrokerAddrs().get(MixAll.MASTER_ID);
                if (masterAddr != null) {
                    BrokerLiveInfo brokerLiveInfo = this.brokerLiveTable.get(masterAddr);
                    if (brokerLiveInfo != null) {
                        result.setHaServerAddr(brokerLiveInfo.getHaServerAddr());
                        result.setMasterAddr(masterAddr);
                    }
                }
            }
        } finally {
            // 2. 释放写锁
            this.lock.writeLock().unlock();
        }
    } catch (Exception e) {
        log.error("registerBroker Exception", e);
    }

    return result;
}

2、读操作：查询主题信息，操作读锁

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public byte[] getAllTopicList() {
    TopicList topicList = new TopicList();
    try {
        try {
            this.lock.readLock().lockInterruptibly();
            topicList.getTopicList().addAll(this.topicQueueTable.keySet());
        } finally {
            this.lock.readLock().unlock();
        }
    } catch (Exception e) {
        log.error("getAllTopicList Exception", e);
    }

    return topicList.encode();
}

我们可以将 NameServer 实现注册中⼼的⽅式总结为： RPC 服务 + HashMap 存储容器 + 读写锁 + 定时任务 。

1、NameServer 监听固定的端⼝，提供 RPC 服务

2、HashMap 作为存储容器

3、读写锁控制锁的颗粒度

4、定时任务 每个 Broker

每隔 30 秒注册主题的路由信息到所有 NameServer NameServer 定时任务每隔10 秒清除已宕机的 Broker , 判断宕机的标准是：当前时间减去 Broker 最后⼀次⼼跳时 间⼤于2分钟

4. ZK VS NS

为什么rocketmq不适用zk作为注册中心呢？

image-20240504155316640

CAP 理论是分布式架构中重要理论。

1、⼀致性( Consistency ) ：所有节点在同⼀时间具有相同的数据 ;

2、可⽤性( Availability ) ：保证每个请求不管成功或者失败都有响应 (某个系统的某个节点挂了，但是并不影响系统的 接受或者发出请求) ;

3、分隔容忍( Partition tolerance ) ：系统中任意信息的丢失或失败不会影响系统的继续运作。 (在整个系统中某个部 分，挂掉了，或者宕机了，并不影响整个系统的运作或者说使⽤) 。

Zookeeper 是⼀个典型的 CP 注册中⼼ ，通过使 ZAB 协议来保证节点之间数据的强⼀致性。

淘宝中间件博客出了⼀篇⽂章 : 阿里巴巴为什么不用 ZooKeeper 做服务发现？-阿里云开发者社区 (aliyun.com)

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1、当数据中⼼服务规模超过⼀定数量 ( 服务规模=F{服务 pub 数,服务 sub 数} )，作为注册中⼼的 ZooKeeper 很快就会 像下图的驴⼦⼀样不堪重负。

2、可以使⽤ ZooKeeper，但是⼤数据请向左，⽽交易则向右，分布式协调向左，服务发现向右。

NameServer 是⼀个典型的 AP 注册中⼼，它有如下优点：

1、代码不到 1000 ⾏，实现简单，易于维护 ;

2、性能极好，除了⽹络消耗，基本都是本地内存操作 ;

3、服务都是⽆状态，且节点之间并不交互，运维简单；

笔者⼀直认为：没有完美的技术，只有最合适的技术，架构设计之道在于简单⾼效和适当妥协。

快来参与讨论吧~

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