RocketMQ—NameServer总结及核心源码剖析

一、NameServer介绍

NameServer 是专为 RocketMQ 设计的轻量级名称服务，具有简单、可集群横向扩展、无状态，节点之间互不通信等特点。整个Rocketmq集群的工作原理如下图所示:

可以看到，RocketMQ架构上主要分为四部分, Broker、Producer、Consumer、NameServer，其他三个都会与NameServer进行通信：

• NameServer: 一个简单的Topic路由注册中心，其角色类似Dubbo中的zookeeper，支持Broker的动态注册与发现。

主要包括两个功能：

1. Broker管理:NameServer接受Broker的注册请求,处理请求数据作为路由信息的基础数据。对broker进行心跳检测机制，检测是否还存活(120s)；
2. topic路由信息管理:每个NameServer都保存整个Broker集群的路由信息，用于Producer和Conumser查询的路由信息，从而进行消息的投递和消费。

• Producer: 消息发布的角色，可集群部署。通过NameServer集群获得Topic的路由信息，包括Topic下面有哪些Queue，这些Queue分布在哪些Broker上等。(Producer只会将消息发送到Master节点，因此只需与Master节点建立连接)。
• Consumer: 消息消费的角色，可集群部署。通过NameServer集群获得Topic的路由信息，连接到对应的Broker上拉取和消费消息。(Master和Slave都可以拉取消息，因此Consumer会与Master和Slave都建立连接)。
• Broker: 主要负责消息的存储、投递和查询以及服务高可用保证。

二、为什么要使用NameServer？

目前可以作为服务发现组件有很多，如etcd、consul、zookeeper、nacos等：

那么为什么rocketmq选择自己开发一个NameServer，而不是使用这些开源组件呢？原因如下：

• RocketMQ的架构设计决定了只需一个轻量级的元数据服务器，只需保持最终一致，而不需要Zookeeper的强一致性解决方案，无需再依赖另一个中间件，从而减少整体维护成本。
• NameServer互相独立，彼此没有通信关系，由于Broker向每个NameServer注册自己的路由信息，所以每个NameServer都保存一份完整的路由信息，单台NameServer挂掉，Broker仍然可以向其它NameServer同步路由信息，不影响其他NameServer，所以Producer,Consumer仍然可以动态感知Broker的路由的信息。

三、NameServer 内部解密

NameServer的路由数据来源是broker注册提供，然后内部加工处理，而路由的数据的使用者是producer和consumer，接下来将着重解析NameServer的路由数据结构，路由注册/查询、broker动态等检测核心逻辑(源码)。 3.1 路由数据结构RouteInfoManager是NameServer核心逻辑类,其代码作用就是维护路由信息管理，提供路由注册/查询等核心功能，由于路由信息都是保存在NameServer应用内存里，其本质就是维护HashMap,而为了防止并发操作，添加了ReentrantReadWriteLock读写锁，简单代码描述如下：

public class RouteInfoManager {
    private static final InternalLogger log = InternalLoggerFactory.getLogger(LoggerName.NAMESRV_LOGGER_NAME);
    // NameServer 与 Broker 空闲时长，默认2分钟，在2分钟内 Nameserver 没有收到 Broker 的心跳包，则关闭该连接。
    private final static long BROKER_CHANNEL_EXPIRED_TIME = 1000 * 60 * 2;
    //读写锁
    private final ReadWriteLock lock = new ReentrantReadWriteLock();
    // Topic,以及对应的队列信息 --消息发送时根据路由表进行负载均衡 。
    private final HashMap<String/* topic */, List<QueueData>> topicQueueTable;
    // 以BrokerName为单位的Broker集合(Broker基础信息，包含 brokerName、所属集群名称、主备 Broker地址。)
    private final HashMap<String/* brokerName */, BrokerData> brokerAddrTable;
    // 集群以及属于该进群的Broker列表(根据一个集群名，获得对应的一组BrokerName的列表)
    private final HashMap<String/* clusterName */, Set<String/* brokerName */>> clusterAddrTable;
    // 存活的Broker地址列表 (NameServer 每次收到心跳包时会 替换该信息 )
    private final HashMap<String/* brokerAddr */, BrokerLiveInfo> brokerLiveTable;
    // Broker对应的Filter Server列表-消费端拉取消息用到
    private final HashMap<String/* brokerAddr */, List<String>/* Filter Server */> filterServerTable;
    ...省略...
}

可以通过以下类图更清楚查看其关系：

QueueData 属性解析:

/**
 * 队列信息
 */
public class QueueData implements Comparable<QueueData> {
    // 队列所属的Broker名称
    private String brokerName;
    // 读队列数量 默认：16
    private int readQueueNums;
    // 写队列数量 默认：16
    private int writeQueueNums;
    //todo Topic的读写权限(2是写 4是读 6是读写)
    private int perm;
    /** 同步复制还是异步复制--对应TopicConfig.topicSysFlag
     * {@link org.apache.rocketmq.common.sysflag.TopicSysFlag}
     */
    private int topicSynFlag;
        ...省略...
 }
map: topicQueueTable 数据格式demo(json)：
{
    "TopicTest":[
        {
            "brokerName":"broker-a",
            "perm":6,
            "readQueueNums":4,
            "topicSynFlag":0,
            "writeQueueNums":4
        }
    ]
}

BrokerData 属性解析:

/**
 * broker的数据:Master与Slave 的对应关系通过指定相同的BrokerName，不同的BrokerId来定义，BrokerId为0 表示Master，非0表示Slave。
 */
public class BrokerData implements Comparable<BrokerData> {
    // broker所属集群
    private String cluster;
    // brokerName
    private String brokerName;
    // 同一个brokerName下可以有一个Master和多个Slave,所以brokerAddrs是一个集合
    // brokerld=O表示 Master，大于 O表示从 Slave
    private HashMap<Long/* brokerId */, String/* broker address */> brokerAddrs;
    // 用于查找broker地址
    private final Random random = new Random();
    ...省略...
 }
map: brokerAddrTable 数据格式demo(json)：
{
    "broker-a":{
        "brokerAddrs":{
            "0":"172.16.62.75:10911"
        },
        "brokerName":"broker-a",
        "cluster":"DefaultCluster"
    }
}

BrokerLiveInfo 属性解析：

/**
 *  存放存活的Broker信息，当前存活的 Broker,该信息不是实时的，NameServer 每10S扫描一次所有的 broker,根据心跳包的时间得知 broker的状态，
 *  该机制也是导致当一个 Broker 进程假死后，消息生产者无法立即感知，可能继续向其发送消息，导致失败（非高可用）
 */
class BrokerLiveInfo {
    //最后一次更新时间
    private long lastUpdateTimestamp;
    //版本号信息
    private DataVersion dataVersion;
    //Netty的Channel
    private Channel channel;
    //HA Broker的地址 是Slave从Master拉取数据时链接的地址,由brokerIp2+HA端口构成
    private String haServerAddr;
    ...省略...
 }
 map: brokerLiveTable 数据格式demo(json)：
 {
    "172.16.62.75:10911":{
        "channel":{
            "active":true,
            "inputShutdown":false,
            "open":true,
            "outputShutdown":false,
            "registered":true,
            "writable":true
        },
        "dataVersion":{
            "counter":2,
            "timestamp":1630907813571
        },
        "haServerAddr":"172.16.62.75:10912",
        "lastUpdateTimestamp":1630907814074
    }
}

brokerAddrTable -Map 数据格式demo(json)

{"DefaultCluster":["broker-a"]}

从RouteInfoManager维护的HashMap数据结构和QueueData、BrokerData、BrokerLiveInfo类属性得知,NameServer维护的信息既简单但极其重要。

3.2 路由注册roker主动注册路由信息存在以下几种情况：

1. 启动时向集群中所有的NameServer注册
2. 定时30s向集群中所有NameServer发送心跳包注册
3. 当broker中topic信息发送变更(新增/修改/删除)发送心跳包注册。

但其实对于NameServer来讲，其核心处理逻辑方法就是 RouteInfoManager#registerBroker, 源码分析如下:

RouteInfoManager#registerBroker

public RegisterBrokerResult registerBroker(
    final String clusterName, final String brokerAddr,
    final String brokerName, final long brokerId,
    final String haServerAddr,
    //TopicConfigSerializeWrapper比较复杂的数据结构，主要包含了broker上所有的topic信息
    final TopicConfigSerializeWrapper topicConfigWrapper,
    final List<String> filterServerList, final Channel channel) {
    RegisterBrokerResult result = new RegisterBrokerResult();
    try {
        try {
            this.lock.writeLock().lockInterruptibly(); // 锁
            //1: 此处维护 clusterAddrTable 数据
            Set<String> brokerNames = this.clusterAddrTable.get(clusterName);
            if (null == brokerNames) {
                brokerNames = new HashSet<String>();
                this.clusterAddrTable.put(clusterName, brokerNames);
            }
            brokerNames.add(brokerName);
            //2:此处维护 brokerAddrTable 数据
            boolean registerFirst = false;//是否第一次注册（如果Topic配置信息发生变更或者该broker为第一次注册）
            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);
            }
            //3: 此处维护 topicQueueTable 数据,数据更新操作方法在：createAndUpdateQueueData
            String oldAddr = brokerData.getBrokerAddrs().put(brokerId, brokerAddr);
            registerFirst = registerFirst || (null == oldAddr);
            if (null != topicConfigWrapper
                && MixAll.MASTER_ID == brokerId) { //小知识点：只处理主节点请求，因为备节点的topic信息是同步主节点的
                // 如果Topic配置信息发生变更或者该broker为第一次注册
                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());
                        }
                    }
                }
            }
             //4: 此处维护：brokerLiveTable数据，关键点：BrokerLiveInfo构造器第一个参数：System.currentTimeMillis()，用于存活判断
            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);
            }
            //5-维护：filterServerTable 数据
            if (filterServerList != null) {
                if (filterServerList.isEmpty()) {
                    this.filterServerTable.remove(brokerAddr);
                } else {
                    this.filterServerTable.put(brokerAddr, filterServerList);
                }
            }
            //返回值（如果当前broker为slave节点）则将haServerAddr、masterAddr等信息设置到result返回值中
            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 {
            this.lock.writeLock().unlock();
        }
    } catch (Exception e) {
        log.error("registerBroker Exception", e);
    }
    return result;
}

备注：

createAndUpdateQueueData方法：其实就是维护topicQueueTable的数据，仔细的你肯定会去撸它。

从源码可看出：Broker注册的路由信息对于NameServer来说，其实就是维护clusterAddrTable、brokerAddrTable、topicQueueTable、brokerLiveTable、filterServerTable.其实源码就是这么简单。

3.3 路由删除路由删除有两种方式，一种是broker主动上报删除，一种是NameServer主动删除。虽然对于NameServer来说处理逻辑有点差别，但是你一看就会懂，分析如下：

1. Broker主动上报删除:Broker在正常被关闭的情况下，会执行unregisterBroker指令,向NameServer发送取消注册请求，其核心源码如下：

RouteInfoManager#unregisterBroker

public void unregisterBroker(
    final String clusterName, final String brokerAddr,
    final String brokerName, final long brokerId) {
    try {
        try {
            this.lock.writeLock().lockInterruptibly();
            //1-直接删除 brokerLiveTable 信息，无需判断时间
            BrokerLiveInfo brokerLiveInfo = this.brokerLiveTable.remove(brokerAddr);
            log.info("unregisterBroker, remove from brokerLiveTable {}, {}",
                brokerLiveInfo != null ? "OK" : "Failed",
                brokerAddr
            );
            //2-删除 filterServerTable 信息
            this.filterServerTable.remove(brokerAddr);
            //3-维护删除 brokerAddrTable 信息
            boolean removeBrokerName = false;
            BrokerData brokerData = this.brokerAddrTable.get(brokerName);
            if (null != brokerData) {
                String addr = brokerData.getBrokerAddrs().remove(brokerId);
                log.info("unregisterBroker, remove addr from brokerAddrTable {}, {}",
                    addr != null ? "OK" : "Failed",
                    brokerAddr
                );
                if (brokerData.getBrokerAddrs().isEmpty()) {
                    this.brokerAddrTable.remove(brokerName);
                    log.info("unregisterBroker, remove name from brokerAddrTable OK, {}",
                        brokerName
                    );
                    removeBrokerName = true;
                }
            }
            //4- 维护删除 clusterAddrTable 信息
            if (removeBrokerName) {
                Set<String> nameSet = this.clusterAddrTable.get(clusterName);
                if (nameSet != null) {
                    boolean removed = nameSet.remove(brokerName);
                    log.info("unregisterBroker, remove name from clusterAddrTable {}, {}",
                        removed ? "OK" : "Failed",
                        brokerName);

                    if (nameSet.isEmpty()) {
                        this.clusterAddrTable.remove(clusterName);
                        log.info("unregisterBroker, remove cluster from clusterAddrTable {}",
                            clusterName
                        );
                    }
                }
                //5- 维护删除 topicQueueTable 信息
                this.removeTopicByBrokerName(brokerName);
            }
        } finally {
            this.lock.writeLock().unlock();
        }
    } catch (Exception e) {
        log.error("unregisterBroker Exception", e);
    }
}

备注：

removeTopicByBrokerName 方法：其实就是删除topicQueueTable的数据，仔细的你已有会去撸它。

2. NameServer主动删除:NameServer定时(10s)扫描brokerLiveTable，检测上次心跳包与当前系统时间的时间差，如果时间戳大于120s，则需要移除该Broker信息,其核心源码如下：

RouteInfoManager#scanNotActiveBroker

public void scanNotActiveBroker() {
    Iterator<Entry<String, BrokerLiveInfo>> it = this.brokerLiveTable.entrySet().iterator();
    while (it.hasNext()) {
        Entry<String, BrokerLiveInfo> next = it.next();
        long last = next.getValue().getLastUpdateTimestamp();
        //1- BROKER_CHANNEL_EXPIRED_TIME,默认（1000 * 60 * 2）120s，判断是不是超过120s
        if ((last + BROKER_CHANNEL_EXPIRED_TIME) < System.currentTimeMillis()) {
            RemotingUtil.closeChannel(next.getValue().getChannel());
            it.remove();
            log.warn("The broker channel expired, {} {}ms", next.getKey(), BROKER_CHANNEL_EXPIRED_TIME);
            this.onChannelDestroy(next.getKey(), next.getValue().getChannel());
        }
    }
}
public void onChannelDestroy(String remoteAddr, Channel channel) {
    String brokerAddrFound = null;
    if (channel != null) {
        try {
            try {  //1- 查询需要删除的broker信息
                this.lock.readLock().lockInterruptibly();
                Iterator<Entry<String, BrokerLiveInfo>> itBrokerLiveTable =
                    this.brokerLiveTable.entrySet().iterator();
                while (itBrokerLiveTable.hasNext()) {
                    Entry<String, BrokerLiveInfo> entry = itBrokerLiveTable.next();
                    if (entry.getValue().getChannel() == channel) {
                        brokerAddrFound = entry.getKey();
                        break;
                    }
                }
            } finally {
                this.lock.readLock().unlock();
            }
        } catch (Exception e) {
            log.error("onChannelDestroy Exception", e);
        }
    }
    if (null == brokerAddrFound) {
        brokerAddrFound = remoteAddr;
    } else {
        log.info("the broker's channel destroyed, {}, clean it's data structure at once", brokerAddrFound);
    }
    if (brokerAddrFound != null && brokerAddrFound.length() > 0) {
        try {
            try {
                this.lock.writeLock().lockInterruptibly();
                this.brokerLiveTable.remove(brokerAddrFound); //2-维护删除 brokerLiveTable 信息
                this.filterServerTable.remove(brokerAddrFound); //3-维护删除 filterServerTable 信息
                String brokerNameFound = null;
                boolean removeBrokerName = false;
                Iterator<Entry<String, BrokerData>> itBrokerAddrTable =
                    this.brokerAddrTable.entrySet().iterator(); //4-维护删除 brokerAddrTable 信息
                while (itBrokerAddrTable.hasNext() && (null == brokerNameFound)) {
                    BrokerData brokerData = itBrokerAddrTable.next().getValue();
                    Iterator<Entry<Long, String>> it = brokerData.getBrokerAddrs().entrySet().iterator();
                    while (it.hasNext()) {
                        Entry<Long, String> entry = it.next();
                        Long brokerId = entry.getKey();
                        String brokerAddr = entry.getValue();
                        if (brokerAddr.equals(brokerAddrFound)) {
                            brokerNameFound = brokerData.getBrokerName();
                            it.remove();
                            log.info("remove brokerAddr[{}, {}] from brokerAddrTable, because channel destroyed",
                                brokerId, brokerAddr);
                            break;
                        }
                    }
                    if (brokerData.getBrokerAddrs().isEmpty()) {
                        removeBrokerName = true;
                        itBrokerAddrTable.remove();
                        log.info("remove brokerName[{}] from brokerAddrTable, because channel destroyed",
                            brokerData.getBrokerName());
                    }
                }
                if (brokerNameFound != null && removeBrokerName) {
                    Iterator<Entry<String, Set<String>>> it = this.clusterAddrTable.entrySet().iterator(); // 5-维护删除 clusterAddrTable 信息
                    while (it.hasNext()) {
                        Entry<String, Set<String>> entry = it.next();
                        String clusterName = entry.getKey();
                        Set<String> brokerNames = entry.getValue();
                        boolean removed = brokerNames.remove(brokerNameFound);
                        if (removed) {
                            log.info("remove brokerName[{}], clusterName[{}] from clusterAddrTable, because channel destroyed",
                                brokerNameFound, clusterName);

                            if (brokerNames.isEmpty()) {
                                log.info("remove the clusterName[{}] from clusterAddrTable, because channel destroyed and no broker in this cluster",
                                    clusterName);
                                it.remove();
                            }

                            break;
                        }
                    }
                }
                if (removeBrokerName) {
                    Iterator<Entry<String, List<QueueData>>> itTopicQueueTable =
                        this.topicQueueTable.entrySet().iterator(); // 6- 维护删除：topicQueueTable 信息
                    while (itTopicQueueTable.hasNext()) {
                        Entry<String, List<QueueData>> entry = itTopicQueueTable.next();
                        String topic = entry.getKey();
                        List<QueueData> queueDataList = entry.getValue();

                        Iterator<QueueData> itQueueData = queueDataList.iterator();
                        while (itQueueData.hasNext()) {
                            QueueData queueData = itQueueData.next();
                            if (queueData.getBrokerName().equals(brokerNameFound)) {
                                itQueueData.remove();
                                log.info("remove topic[{} {}], from topicQueueTable, because channel destroyed",
                                    topic, queueData);
                            }
                        }
                        if (queueDataList.isEmpty()) {
                            itTopicQueueTable.remove();
                            log.info("remove topic[{}] all queue, from topicQueueTable, because channel destroyed",
                                topic);
                        }
                    }
                }
            } finally {
                this.lock.writeLock().unlock();
            }
        } catch (Exception e) {
            log.error("onChannelDestroy Exception", e);
        }
    }
}

从源码可看出：Broker取消注册两种方式对于NameServer来说，其实就是删除clusterAddrTable、brokerAddrTable、topicQueueTable、brokerLiveTable、filterServerTable相关信息.

3.4 路由发现RocketMQ路由发现其实是非实时的，当Topic路由出现变化后，NameServer不会主动推送给客户端，而是由生产端和消费端定时拉取主题最新的路由,其核心源码如下：

RouteInfoManager#pickupTopicRouteData
public TopicRouteData pickupTopicRouteData(final String topic) {
    TopicRouteData topicRouteData = new TopicRouteData();
    boolean foundQueueData = false;
    boolean foundBrokerData = false;
    Set<String> brokerNameSet = new HashSet<String>();
    List<BrokerData> brokerDataList = new LinkedList<BrokerData>();
    topicRouteData.setBrokerDatas(brokerDataList);
    HashMap<String, List<String>> filterServerMap = new HashMap<String, List<String>>();
    topicRouteData.setFilterServerTable(filterServerMap);
    try {
        try {
            this.lock.readLock().lockInterruptibly();
            List<QueueData> queueDataList = this.topicQueueTable.get(topic);
            if (queueDataList != null) {
                topicRouteData.setQueueDatas(queueDataList);
                foundQueueData = true;
                Iterator<QueueData> it = queueDataList.iterator();
                while (it.hasNext()) {
                    QueueData qd = it.next();
                    brokerNameSet.add(qd.getBrokerName());
                }
                // 处理构建：BrokerData数据
                for (String brokerName : brokerNameSet) {
                    BrokerData brokerData = this.brokerAddrTable.get(brokerName);
                    if (null != brokerData) {
                        BrokerData brokerDataClone = new BrokerData(brokerData.getCluster(), brokerData.getBrokerName(), (HashMap<Long, String>) brokerData
                            .getBrokerAddrs().clone());
                        brokerDataList.add(brokerDataClone);
                        foundBrokerData = true;
                        for (final String brokerAddr : brokerDataClone.getBrokerAddrs().values()) {
                            List<String> filterServerList = this.filterServerTable.get(brokerAddr);
                            filterServerMap.put(brokerAddr, filterServerList);
                        }
                    }
                }
            }
        } finally {
            this.lock.readLock().unlock();
        }
    } catch (Exception e) {
        log.error("pickupTopicRouteData Exception", e);
    }
    log.debug("pickupTopicRouteData {} {}", topic, topicRouteData);
    if (foundBrokerData && foundQueueData) {
        return topicRouteData;
    }
    return null;
}

备注：

这段代码都不好意思写注释了，其实就是从topicQueueTable、brokerAddrTable、filterServerTable这些Map中查询数据，组装给TopicRouteData，然后返回给客户端使用。

下面列出TopicRouteData简单介绍下的属性，你会发现原来可以如此简单：

public class TopicRouteData extends RemotingSerializable {
    //topic排序的配置，和"ORDER_TOPIC_CONFIG"这个NameSpace有关，参照DefaultRequestProcessor#getRouteInfoByTopic，后续可讲解此小知识点
    private String orderTopicConf;
    // topic 队列元数据
    private List<QueueData> queueDatas;
    // topic分布的 broker元数据
    private List<BrokerData> brokerDatas;
    // broker上过滤服务器地址列表
    private HashMap<String/* brokerAddr */, List<String>/* Filter Server */> filterServerTable;
    ...省略...
}

其实NameServer里面提供了很多其他功能方法，例如：> getBrokerClusterInfo(获取集群信息)，

getAllTopicListFromNameserver(获取所有topic)等，

但大部分都是围绕> clusterAddrTable

brokerAddrTable

topicQueueTable

brokerLiveTable

filterServerTable

这几个hashMap来转。

四、结论

从功能作用角度上总结：NameServer作为RocketMQ的“大脑”，保存着集群MQ的路由信息，具体就是记录维护Topic、Broker的信息，及监控Broker的运行状态，为client提供路由能力；而从源代码的角度总结：NameServer就是维护了多个HashMap，Broker的注册，Client的查询都是围绕其Map操作，当然为了解决并发问题添加了ReentrantReadWriteLock(读写锁). 其实本节只描述了NameServer部分关键代码，其NameServer的启动流程等多处源代码都值得分析和学习，最后我们再通过一张总结图再次回顾一下“NameServer”！

五、问题

细心的你，有没有发现NameServer存在下面这种缺陷:

假设Broker异常宕机，NameServer至少等120s才将该Broker从路由信息中剔除，在Broker故障期间，消息生产者Producer根据topic获取到的路由信息包含已经宕机的Broker，会导致消息在短时间内发送失败，那这种情况怎么办？岂不是消息发送不是高可用的? 消费端消费消息是否存在影响？ 请带着问题解析来将会在发送端和消费端一一为你讲解.

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文章来源：https://mp.weixin.qq.com/s/slu-yS4mrcGEgfOMCCqWNg