微服务组件-----Spring Cloud Alibaba 注册中心Nacos的CP架构Raft协议分析

前言

　　本篇幅是继  注册中心Nacos源码分析 的下半部分。

意义

【1】虽说大部分我们采用注册中心的时候考虑的都是AP架构，为什么呢？因为性能相对于CP架构来说更高，需要等待的时间更少【相对于CP架构，采用的是二段提交，AP架构是直接落盘数据，然后进行数据扩散，来达到最终一致，所以客户端收到响应会更快】；

【2】其次，考虑AP架构会不会存在数据丢失的风险呢？答案是必然的，所以是不是应该考虑CP架构呢？那么问题来了，数据丢失是问题吗？明显不是。基于AP架构的注册中心，明显在客户端那边都会存在重试机制，也就是对于一个集群而言，一台服务器宕机会自动重连到其他机器上去，所以有补充的手段自然也就不考虑CP架构了。

【3】但是对于分布式而言，CP架构确实十分重要的一部分；如zookeeper便是分布式的鼻祖，不过采用的是ZAB强一致性协议，而raft则也是强一致性协议的【两者看似差不多，但也有一些差别】，而且市面上喜欢raft协议的更多。所以研究Raft协议便是比较必要的。

Raft协议详解

【1】演示网站：http://thesecretlivesofdata.com/raft/

【2】Raft定义角色的三种状态

1）Follower state    //追随者
2）Candidate state  //候选者
3）Leader state        //领导者

【3】流程分析

【3.1】所有的节点都以跟随者状态开始的

【3.2】如果追随者没有收到任何领导人的消息，那么他们就可以成为一名候选者【注意：这里的候选者是一个【至于这个候选者是怎么来的还要分析，会不会出现多个的情况，但是能选举成功必然是只有一个候选者】，这也是与ZAB协议的不同之处，ZAB是所有人参与】

【3.3】候选人向其他节点发送投票请求，而节点对投票请求进行回复

【3.4】候选人从大多数节点获得选票，就将成为领导者

【4】数据一致性的流程分析

【4.1】对系统的所有变化现在都要经过领导【哪怕是你请求从节点，从节点也会转发给主节点】，主节点每个更改都将作为节点日志中的一个条目添加，但此日志条目当前未提交，因此不会更新节点的值【注意：此时客户端只是发送了请求还没收到回复】

【4.2】要提交条目，节点首先将其复制到跟踪节点【主节点向从节点发送请求】【一般是通过心跳请求，附带上数据来完成的】

【4.3】领导会等待，直到大多数节点已经写入了条目并回复请求，该条目才会在领导节点上提交【这个时候便会回复客户端的请求】

【4.4】领导再次发送请求通知追随者条目已提交【还是通过心跳进行二次通知】

【4.5】因为标准的Raft中采用的是QUORUM， 即确保至少大部分节点都接收到写操作之后才会返回结果给Client， 而Redis默认采用的实际上是ANY/ONE, 即只要Master节点写入成功后，就立刻返回给Client，然后该写入命令被异步的发送给所有的slave节点，来尽可能地让所有地slave节点与master节点保持一致。

写入类型	解释说明
ZERO	接收到写操作后立即返回，不保证写入成功
ANY/ONE	确保该值被写入至少一个节点
QUORUM	确保至少大多数节点（节点总数/2+1）接受到写操作之后，再返回
ALL	确保所有副本节点都接受到写操作之后，再返回

【5】多节点下出现脑裂问题【Raft如何保持一致】

【5.1】假设有五个分区

【5.2】模拟网络故障导致分区，AB为一组，CDE为一组。【由于分区后，CDE没有了领导者，收不到心跳之后，便会达到选举超时的时间，由于C优先超时便会成为候选者】

【5.3】此时便会出现B和C都成为领导者的情况

【5.4】如果出现数据更新的情况

【5.4.1】人数少的分区收到写入请求是写入不成功的【因为基于大多数写入成功才算是写入成功，所以最终客户端会是写入请求超时】

【5.4.2】相反数目多的分区【在C写入后，通过心跳传递数据给DE，然后收到回复后明显是符合写入节点数大于或等于（节点总数/2+1）】，所以就会返回客户端响应，并在下一次心跳中让DE进行提交。

【5.5】当分区网络恢复后【其实是根据选举周期判断哪个会保留为领导者，其余将回滚未提交的条目，并匹配新领导者的日志】

【5.6】当然这里面还会出现偶数分区【如ABCD，分为AB,CD，那么其实算是两个分区都不可用，毕竟都不满足（4/2+1）为3的写入】

结合源码分析写入数据部分的验证

【1】基于上个篇幅的【1.1.2】分析addInstance注册方法，里面会根据ephemeral字段属性判断是持久节点还是临时节点

【1.1】RaftConsistencyServiceImpl类#put方法

@Override
public void put(String key, Record value) throws NacosException {
    checkIsStopWork();
    try {
        //利用自己实现的raftCore类
        raftCore.signalPublish(key, value);
    } catch (Exception e) {
        Loggers.RAFT.error("Raft put failed.", e);
        throw new NacosException(...);
    }
}

【1.2】raftCore类#signalPublish方法是怎么发送和处理数据的【重点】

/**
 * Signal publish new record. If not leader, signal to leader. If leader, try to commit publish.
 *
 * @param key   key
 * @param value value
 * @throws Exception any exception during publish
 */
public void signalPublish(String key, Record value) throws Exception {
    if (stopWork) {
        throw new IllegalStateException("old raft protocol already stop work");
    }
    //验证了只有领导者才有权利进行写入
    if (!isLeader()) {
        ObjectNode params = JacksonUtils.createEmptyJsonNode();
        params.put("key", key);
        params.replace("value", JacksonUtils.transferToJsonNode(value));
        Map<String, String> parameters = new HashMap<>(1);
        parameters.put("key", key);

        final RaftPeer leader = getLeader();
        //非领导者将利用请求转发给领导者，待领导者回复后回复
        raftProxy.proxyPostLarge(leader.ip, API_PUB, params.toString(), parameters);
        return;
    }

    OPERATE_LOCK.lock();
    try {
        final long start = System.currentTimeMillis();
        final Datum datum = new Datum();
        datum.key = key;
        datum.value = value;
        if (getDatum(key) == null) {
            datum.timestamp.set(1L);
        } else {
            datum.timestamp.set(getDatum(key).timestamp.incrementAndGet());
        }

        ObjectNode json = JacksonUtils.createEmptyJsonNode();
        json.replace("datum", JacksonUtils.transferToJsonNode(datum));
        json.replace("source", JacksonUtils.transferToJsonNode(peers.local()));
        //进行数据的发布【1.3】
        onPublish(datum, peers.local());

        //接下来这一片，便是数据一致性的实现，大体为
        //先将数据转成json，然后是发起异步请求【不阻塞，会有回调处理】
        //利用CountDownLatch阻塞： peers.size() / 2 + 1，来达成raft的大部分节点响应部分。
        //满足就回复客户端，不满足就阻塞至请求超时
        final String content = json.toString();

        final CountDownLatch latch = new CountDownLatch(peers.majorityCount());
        for (final String server : peers.allServersIncludeMyself()) {
            if (isLeader(server)) {
                latch.countDown();
                continue;
            }
            final String url = buildUrl(server, API_ON_PUB);
            HttpClient.asyncHttpPostLarge(url, Arrays.asList("key", key), content, new Callback<String>() {
                @Override
                public void onReceive(RestResult<String> result) {
                    if (!result.ok()) {
                        Loggers.RAFT
                                .warn("[RAFT] failed to publish data to peer, datumId={}, peer={}, http code={}",
                                        datum.key, server, result.getCode());
                        return;
                    }
                    latch.countDown();
                }

                @Override
                public void onError(Throwable throwable) {
                    Loggers.RAFT.error("[RAFT] failed to publish data to peer", throwable);
                }

                @Override
                public void onCancel() {

                }
            });

        }

        if (!latch.await(UtilsAndCommons.RAFT_PUBLISH_TIMEOUT, TimeUnit.MILLISECONDS)) {
            // only majority servers return success can we consider this update success
            Loggers.RAFT.error("data publish failed, caused failed to notify majority, key={}", key);
            throw new IllegalStateException("data publish failed, caused failed to notify majority, key=" + key);
        }

        long end = System.currentTimeMillis();
        Loggers.RAFT.info("signalPublish cost {} ms, key: {}", (end - start), key);
    } finally {
        OPERATE_LOCK.unlock();
    }
}

【1.3】分析数据发布的onPublish方法

/**
 * Do publish. If leader, commit publish to store. If not leader, stop publish because should signal to leader.
 *
 * @param datum  datum
 * @param source source raft peer
 * @throws Exception any exception during publish
 */
public void onPublish(Datum datum, RaftPeer source) throws Exception {
    if (stopWork) {
        throw new IllegalStateException("old raft protocol already stop work");
    }
    RaftPeer local = peers.local();
    if (datum.value == null) {
        Loggers.RAFT.warn("received empty datum");
        throw new IllegalStateException("received empty datum");
    }

    if (!peers.isLeader(source.ip)) {
        Loggers.RAFT
                .warn("peer {} tried to publish data but wasn't leader, leader: {}", JacksonUtils.toJson(source),
                        JacksonUtils.toJson(getLeader()));
        throw new IllegalStateException("peer(" + source.ip + ") tried to publish " + "data but wasn't leader");
    }

    if (source.term.get() < local.term.get()) {
        Loggers.RAFT.warn("out of date publish, pub-term: {}, cur-term: {}", JacksonUtils.toJson(source),
                JacksonUtils.toJson(local));
        throw new IllegalStateException(
                "out of date publish, pub-term:" + source.term.get() + ", cur-term: " + local.term.get());
    }

    local.resetLeaderDue();

    // if data should be persisted, usually this is true:
    if (KeyBuilder.matchPersistentKey(datum.key)) {
        raftStore.write(datum);  //写入磁盘
    }

    datums.put(datum.key, datum);

    if (isLeader()) {
        local.term.addAndGet(PUBLISH_TERM_INCREASE_COUNT);
    } else {
        if (local.term.get() + PUBLISH_TERM_INCREASE_COUNT > source.term.get()) {
            //set leader term:
            getLeader().term.set(source.term.get());
            local.term.set(getLeader().term.get());
        } else {
            local.term.addAndGet(PUBLISH_TERM_INCREASE_COUNT);
        }
    }
    raftStore.updateTerm(local.term.get());
    NotifyCenter.publishEvent(ValueChangeEvent.builder().key(datum.key).action(DataOperation.CHANGE).build());  //发布事件，异步写入内存
    Loggers.RAFT.info("data added/updated, key={}, term={}", datum.key, local.term);
}

【1.4】进行磁盘的写入【同步的】

/**
 * Write datum to cache file.
 *
 * @param datum datum
 * @throws Exception any exception during writing
 */
public synchronized void write(final Datum datum) throws Exception {

    String namespaceId = KeyBuilder.getNamespace(datum.key);

    File cacheFile = new File(cacheFileName(namespaceId, datum.key));

    if (!cacheFile.exists() && !cacheFile.getParentFile().mkdirs() && !cacheFile.createNewFile()) {
        MetricsMonitor.getDiskException().increment();

        throw new IllegalStateException("can not make cache file: " + cacheFile.getName());
    }

    ByteBuffer data;

    data = ByteBuffer.wrap(JacksonUtils.toJson(datum).getBytes(StandardCharsets.UTF_8));

    try (FileChannel fc = new FileOutputStream(cacheFile, false).getChannel()) {
        fc.write(data, data.position());
        fc.force(true);
    } catch (Exception e) {
        MetricsMonitor.getDiskException().increment();
        throw e;
    }

    // remove old format file:
    if (StringUtils.isNoneBlank(namespaceId)) {
        if (datum.key.contains(Constants.DEFAULT_GROUP + Constants.SERVICE_INFO_SPLITER)) {
            String oldDatumKey = datum.key
                    .replace(Constants.DEFAULT_GROUP + Constants.SERVICE_INFO_SPLITER, StringUtils.EMPTY);

            cacheFile = new File(cacheFileName(namespaceId, oldDatumKey));
            if (cacheFile.exists() && !cacheFile.delete()) {
                Loggers.RAFT.error("[RAFT-DELETE] failed to delete old format datum: {}, value: {}", datum.key,
                        datum.value);
                throw new IllegalStateException("failed to delete old format datum: " + datum.key);
            }
        }
    }
}

private String cacheFileName(String namespaceId, String datumKey) {
    String fileName;
    if (StringUtils.isNotBlank(namespaceId)) {
        //对应集群节点下面的data/naming/data/public下面
        fileName = CACHE_DIR + File.separator + namespaceId + File.separator + encodeDatumKey(datumKey);
    } else {
        fileName = CACHE_DIR + File.separator + encodeDatumKey(datumKey);
    }
    return fileName;
}

【1.5】发布事件写入内存【异步的】

//使用快捷键 Ctrl+Shift+f 或 通过 Edit —> Find —>Find In Path 检索 ValueChangeEvent 看对应的 onEvent处理
PersistentNotifier类#onEvent方法
@Override
public void onEvent(ValueChangeEvent event) {
    notify(event.getKey(), event.getAction(), find.apply(event.getKey()));
}

public <T extends Record> void notify(final String key, final DataOperation action, final T value) {
    if (listenerMap.containsKey(KeyBuilder.SERVICE_META_KEY_PREFIX)) {
        if (KeyBuilder.matchServiceMetaKey(key) && !KeyBuilder.matchSwitchKey(key)) {
            for (RecordListener listener : listenerMap.get(KeyBuilder.SERVICE_META_KEY_PREFIX)) {
                try {
                    if (action == DataOperation.CHANGE) {
                        listener.onChange(key, value);
                    }
                    if (action == DataOperation.DELETE) {
                        listener.onDelete(key);
                    }
                } catch (Throwable e) {
                    Loggers.RAFT.error("[NACOS-RAFT] error while notifying listener of key: {}", key, e);
                }
            }
        }
    }

    if (!listenerMap.containsKey(key)) {
        return;
    }

    for (RecordListener listener : listenerMap.get(key)) {
        try {
            if (action == DataOperation.CHANGE) {
                listener.onChange(key, value);
                continue;
            }
            if (action == DataOperation.DELETE) {
                listener.onDelete(key);
            }
        } catch (Throwable e) {
            Loggers.RAFT.error("[NACOS-RAFT] error while notifying listener of key: {}", key, e);
        }
    }
}

Service类#onChange方法
@Override
public void onChange(String key, Instances value) throws Exception {

    Loggers.SRV_LOG.info("[NACOS-RAFT] datum is changed, key: {}, value: {}", key, value);

    for (Instance instance : value.getInstanceList()) {

        if (instance == null) {
            // Reject this abnormal instance list:
            throw new RuntimeException("got null instance " + key);
        }

        if (instance.getWeight() > 10000.0D) {
            instance.setWeight(10000.0D);
        }

        if (instance.getWeight() < 0.01D && instance.getWeight() > 0.0D) {
            instance.setWeight(0.01D);
        }
    }

    updateIPs(value.getInstanceList(), KeyBuilder.matchEphemeralInstanceListKey(key));

    recalculateChecksum();
}

结合源码分析选举部分的验证

【1】核心类RaftCore类#init()

【1.1】重点说明：该方法利用的是Spring的特性@PostConstruct注解，在初始化类的时候自动启动了两个重要的定时任务【选举任务（MasterElection）和心跳任务（HeartBeat）】

【1.2】代码展示

【2】选举任务的分析

【2.1】选举定时器代码展示

//对选举任务进行注册
public static ScheduledFuture registerMasterElection(Runnable runnable) {
    return NAMING_TIMER_EXECUTOR.scheduleAtFixedRate(runnable, 0, TICK_PERIOD_MS, TimeUnit.MILLISECONDS);
}

//从GlobalExecutor类中可以看出，默认的线程数量为JVM可用超线程的两倍
private static final ScheduledExecutorService NAMING_TIMER_EXECUTOR = ExecutorFactory.Managed
            .newScheduledExecutorService(ClassUtils.getCanonicalName(NamingApp.class),
                    Runtime.getRuntime().availableProcessors() * 2,
                    new NameThreadFactory("com.alibaba.nacos.naming.timer"));

【2.2】选举任务代码展示【在这里你会发现，一个bug，如果先苏醒的节点是缺失数据的节点呢，那么节点必然会丢失，但是这个问题并不严重，就和AP架构是一样的，客户端会重新建立连接补全数据】

public class MasterElection implements Runnable {

    @Override
    public void run() {
        try {
            if (stopWork) {
                return;
            }
            if (!peers.isReady()) {
                return;
            }

            //这个实在选举的时候会产生
            //（而其中的休眠时间是，随机时间是0-15s，与数据量无关，所以选举出来的leader不一定是数据最全的）
            RaftPeer local = peers.local();
            //定时任务默认是500MS
            local.leaderDueMs -= GlobalExecutor.TICK_PERIOD_MS;

            if (local.leaderDueMs > 0) {
                return;
            }

            // reset timeout
            //重置选举时间【15s-20s】
            local.resetLeaderDue();
            //重置心跳时间5s
            local.resetHeartbeatDue();
            //发起投票
            sendVote();
        } catch (Exception e) {
            Loggers.RAFT.warn("[RAFT] error while master election {}", e);
        }

    }

    private void sendVote() {

        RaftPeer local = peers.get(NetUtils.localServer());
        Loggers.RAFT.info(...);

        //将之前的选票信息清空
        peers.reset();
        //增加选举周期
        local.term.incrementAndGet();
        local.voteFor = local.ip;
        //设置当前节点为候选者
        local.state = RaftPeer.State.CANDIDATE;

        Map<String, String> params = new HashMap<>(1);
        params.put("vote", JacksonUtils.toJson(local));
        //遍历集群
        for (final String server : peers.allServersWithoutMySelf()) {
            final String url = buildUrl(server, API_VOTE);
            try {
                //发送异步请求
                HttpClient.asyncHttpPost(url, null, params, new Callback<String>() {
                    @Override
                    public void onReceive(RestResult<String> result) {
                        if (!result.ok()) {
                            Loggers.RAFT.error("NACOS-RAFT vote failed: {}, url: {}", result.getCode(), url);
                            return;
                        }

                        RaftPeer peer = JacksonUtils.toObj(result.getData(), RaftPeer.class);

                        Loggers.RAFT.info("received approve from peer: {}", JacksonUtils.toJson(peer));

                        peers.decideLeader(peer);

                    }

                    @Override
                    public void onError(Throwable throwable) {...}

                    @Override
                    public void onCancel() {}
                });
            } catch (Exception e) {...}
        }
    }
}

//异步情况下对于受到回复
public RaftPeer decideLeader(RaftPeer candidate) {
    peers.put(candidate.ip, candidate);

    SortedBag ips = new TreeBag();
    int maxApproveCount = 0;
    String maxApprovePeer = null;
    for (RaftPeer peer : peers.values()) {
        if (StringUtils.isEmpty(peer.voteFor)) {
            continue;
        }

        ips.add(peer.voteFor);
        if (ips.getCount(peer.voteFor) > maxApproveCount) {
            maxApproveCount = ips.getCount(peer.voteFor);
            maxApprovePeer = peer.voteFor;
        }
    }

    if (maxApproveCount >= majorityCount()) {
        RaftPeer peer = peers.get(maxApprovePeer);
        peer.state = RaftPeer.State.LEADER;

        if (!Objects.equals(leader, peer)) {
            leader = peer;
            ApplicationUtils.publishEvent(new LeaderElectFinishedEvent(this, leader, local()));
            Loggers.RAFT.info("{} has become the LEADER", leader.ip);
        }
    }

    return leader;
}

【2.3】接收到选票的处理

//RaftController类
@PostMapping("/vote")
public JsonNode vote(HttpServletRequest request, HttpServletResponse response) throws Exception {
    if (versionJudgement.allMemberIsNewVersion()) {
        throw new IllegalStateException("old raft protocol already stop");
    }
    RaftPeer peer = raftCore.receivedVote(JacksonUtils.toObj(WebUtils.required(request, "vote"), RaftPeer.class));

    return JacksonUtils.transferToJsonNode(peer);
}

public synchronized RaftPeer receivedVote(RaftPeer remote) {
    if (stopWork) {
        throw new IllegalStateException("old raft protocol already stop work");
    }
    if (!peers.contains(remote)) {
        throw new IllegalStateException("can not find peer: " + remote.ip);
    }

    RaftPeer local = peers.get(NetUtils.localServer());
    //这种其实是应对两个节点都发送了选票环节，那么肯定不会去选对方
    if (remote.term.get() <= local.term.get()) {
        String msg = "received illegitimate vote" + ", voter-term:" + remote.term + ", votee-term:" + local.term;

        Loggers.RAFT.info(msg);
        if (StringUtils.isEmpty(local.voteFor)) {
            local.voteFor = local.ip;
        }

        return local;
    }
    //将选举时间重置，保证这次选举不成功会进入下一轮休眠
    local.resetLeaderDue();

    local.state = RaftPeer.State.FOLLOWER;
    local.voteFor = remote.ip;
    //这里的周期变更的原因是，如果这轮选举不成功的话，下一轮万一我先醒了保证选举周期是最大的
    local.term.set(remote.term.get());

    Loggers.RAFT.info("vote {} as leader, term: {}", remote.ip, remote.term);

    return local;
}

【3】心跳任务的分析

【3.1】心跳定时器代码展示

//定义了心跳任务500ms一次，而且与选举任务是同一个定时器
public static ScheduledFuture registerHeartbeat(Runnable runnable) {
    return NAMING_TIMER_EXECUTOR.scheduleWithFixedDelay(runnable, 0, TICK_PERIOD_MS, TimeUnit.MILLISECONDS);
}

【3.2】心跳任务代码展示【说白了也就是会发送列表的key值【减少数据量，而对应从节点自动拉取来补全数据】过去，采用时间戳作为版本号】

public class HeartBeat implements Runnable {

    //非领导者不可发心跳
    @Override
    public void run() {
        try {
            if (stopWork) {
                return;
            }
            if (!peers.isReady()) {
                return;
            }

            RaftPeer local = peers.local();
            //心跳时间设置在5s内的随机数值
            local.heartbeatDueMs -= GlobalExecutor.TICK_PERIOD_MS;
            if (local.heartbeatDueMs > 0) {
                return;
            }

            local.resetHeartbeatDue();

            sendBeat();
        } catch (Exception e) {...}

    }

    private void sendBeat() throws IOException, InterruptedException {
        RaftPeer local = peers.local();
        if (EnvUtil.getStandaloneMode() || local.state != RaftPeer.State.LEADER) {
            return;
        }
        if (Loggers.RAFT.isDebugEnabled()) {..日志部分忽略..}

        local.resetLeaderDue();

        // build data
        ObjectNode packet = JacksonUtils.createEmptyJsonNode();
        packet.replace("peer", JacksonUtils.transferToJsonNode(local));

        ArrayNode array = JacksonUtils.createEmptyArrayNode();

        if (switchDomain.isSendBeatOnly()) {
            Loggers.RAFT.info("[SEND-BEAT-ONLY] {}", switchDomain.isSendBeatOnly());
        }

        if (!switchDomain.isSendBeatOnly()) {
            for (Datum datum : datums.values()) {

                ObjectNode element = JacksonUtils.createEmptyJsonNode();

                if (KeyBuilder.matchServiceMetaKey(datum.key)) {
                    element.put("key", KeyBuilder.briefServiceMetaKey(datum.key));
                } else if (KeyBuilder.matchInstanceListKey(datum.key)) {
                    element.put("key", KeyBuilder.briefInstanceListkey(datum.key));
                }
                //利用时间戳来当版本号
                element.put("timestamp", datum.timestamp.get());

                array.add(element);
            }
        }

        packet.replace("datums", array);
        // broadcast
        Map<String, String> params = new HashMap<String, String>(1);
        params.put("beat", JacksonUtils.toJson(packet));

        String content = JacksonUtils.toJson(params);

        ByteArrayOutputStream out = new ByteArrayOutputStream();
        GZIPOutputStream gzip = new GZIPOutputStream(out);
        gzip.write(content.getBytes(StandardCharsets.UTF_8));
        gzip.close();

        byte[] compressedBytes = out.toByteArray();
        String compressedContent = new String(compressedBytes, StandardCharsets.UTF_8);

        if (Loggers.RAFT.isDebugEnabled()) {
            Loggers.RAFT.debug("raw beat data size: {}, size of compressed data: {}", content.length(),
                    compressedContent.length());
        }

        for (final String server : peers.allServersWithoutMySelf()) {
            try {
                final String url = buildUrl(server, API_BEAT);
                if (Loggers.RAFT.isDebugEnabled()) {
                    Loggers.RAFT.debug("send beat to server " + server);
                }
                HttpClient.asyncHttpPostLarge(url, null, compressedBytes, new Callback<String>() {
                    @Override
                    public void onReceive(RestResult<String> result) {
                        if (!result.ok()) {
                            Loggers.RAFT.error("NACOS-RAFT beat failed: {}, peer: {}", result.getCode(), server);
                            MetricsMonitor.getLeaderSendBeatFailedException().increment();
                            return;
                        }

                        peers.update(JacksonUtils.toObj(result.getData(), RaftPeer.class));
                        if (Loggers.RAFT.isDebugEnabled()) {
                            Loggers.RAFT.debug("receive beat response from: {}", url);
                        }
                    }

                    @Override
                    public void onError(Throwable throwable) {
                        Loggers.RAFT.error("NACOS-RAFT error while sending heart-beat to peer: {} {}", server,
                                throwable);
                        MetricsMonitor.getLeaderSendBeatFailedException().increment();
                    }

                    @Override
                    public void onCancel() {

                    }
                });
            } catch (Exception e) {
                Loggers.RAFT.error("error while sending heart-beat to peer: {} {}", server, e);
                MetricsMonitor.getLeaderSendBeatFailedException().increment();
            }
        }

    }
}

【3.3】接收到心跳的处理

//RaftController类
@PostMapping("/beat")
public JsonNode beat(HttpServletRequest request, HttpServletResponse response) throws Exception {
    if (versionJudgement.allMemberIsNewVersion()) {
        throw new IllegalStateException("old raft protocol already stop");
    }
    //解压，转义
    String entity = new String(IoUtils.tryDecompress(request.getInputStream()), StandardCharsets.UTF_8);
    String value = URLDecoder.decode(entity, "UTF-8");
    value = URLDecoder.decode(value, "UTF-8");

    JsonNode json = JacksonUtils.toObj(value);

    RaftPeer peer = raftCore.receivedBeat(JacksonUtils.toObj(json.get("beat").asText()));

    return JacksonUtils.transferToJsonNode(peer);
}

//处理心跳请求
public RaftPeer receivedBeat(JsonNode beat) throws Exception {
    if (stopWork) {
        throw new IllegalStateException("old raft protocol already stop work");
    }
    final RaftPeer local = peers.local();
    final RaftPeer remote = new RaftPeer();
    JsonNode peer = beat.get("peer");
    remote.ip = peer.get("ip").asText();
    remote.state = RaftPeer.State.valueOf(peer.get("state").asText());
    remote.term.set(peer.get("term").asLong());
    remote.heartbeatDueMs = peer.get("heartbeatDueMs").asLong();
    remote.leaderDueMs = peer.get("leaderDueMs").asLong();
    remote.voteFor = peer.get("voteFor").asText();

    if (remote.state != RaftPeer.State.LEADER) {
        Loggers.RAFT.info("[RAFT] invalid state from master, state: {}, remote peer: {}", remote.state,
                JacksonUtils.toJson(remote));
        throw new IllegalArgumentException("invalid state from master, state: " + remote.state);
    }

    if (local.term.get() > remote.term.get()) {
        Loggers.RAFT
                .info("[RAFT] out of date beat, beat-from-term: {}, beat-to-term: {}, remote peer: {}, and leaderDueMs: {}",
                        remote.term.get(), local.term.get(), JacksonUtils.toJson(remote), local.leaderDueMs);
        throw new IllegalArgumentException(
                "out of date beat, beat-from-term: " + remote.term.get() + ", beat-to-term: " + local.term.get());
    }

    if (local.state != RaftPeer.State.FOLLOWER) {

        Loggers.RAFT.info("[RAFT] make remote as leader, remote peer: {}", JacksonUtils.toJson(remote));
        // mk follower
        local.state = RaftPeer.State.FOLLOWER;
        local.voteFor = remote.ip;
    }

    final JsonNode beatDatums = beat.get("datums");
    //重置心跳和选举任务的时间，这一步确保当领导者宕机后，集群节点因为没有收到领导者的心跳而重新发起选举
    local.resetLeaderDue();
    local.resetHeartbeatDue();

    peers.makeLeader(remote);

    if (!switchDomain.isSendBeatOnly()) {

        Map<String, Integer> receivedKeysMap = new HashMap<>(datums.size());
        //先将本地数据设置为0，后面将领导有的设置为1，最后面根据设置还为0的便是要删除的
        for (Map.Entry<String, Datum> entry : datums.entrySet()) {
            receivedKeysMap.put(entry.getKey(), 0);
        }

        // now check datums
        List<String> batch = new ArrayList<>();

        int processedCount = 0;
        if (Loggers.RAFT.isDebugEnabled()) {
            Loggers.RAFT
                    .debug("[RAFT] received beat with {} keys, RaftCore.datums' size is {}, remote server: {}, term: {}, local term: {}",
                            beatDatums.size(), datums.size(), remote.ip, remote.term, local.term);
        }
        for (Object object : beatDatums) {
            processedCount = processedCount + 1;

            JsonNode entry = (JsonNode) object;
            String key = entry.get("key").asText();
            final String datumKey;

            if (KeyBuilder.matchServiceMetaKey(key)) {
                datumKey = KeyBuilder.detailServiceMetaKey(key);
            } else if (KeyBuilder.matchInstanceListKey(key)) {
                datumKey = KeyBuilder.detailInstanceListkey(key);
            } else {
                // ignore corrupted key:
                continue;
            }

            long timestamp = entry.get("timestamp").asLong();

            receivedKeysMap.put(datumKey, 1);

            try {
                if (datums.containsKey(datumKey) && datums.get(datumKey).timestamp.get() >= timestamp
                        && processedCount < beatDatums.size()) {
                    continue;
                }

                if (!(datums.containsKey(datumKey) && datums.get(datumKey).timestamp.get() >= timestamp)) {
                    batch.add(datumKey);
                }

                //利用批处理来提高性能，满五十条进行一次处理
                //或者不满但是，现在已经到了最后了，就再一批次全部处理
                if (batch.size() < 50 && processedCount < beatDatums.size()) {
                    continue;
                }

                String keys = StringUtils.join(batch, ",");

                //如果批次里面没有数据就不进行处理
                if (batch.size() <= 0) {
                    continue;
                }

                Loggers.RAFT.info("get datums from leader: {}, batch size is {}, processedCount is {}"
                                + ", datums' size is {}, RaftCore.datums' size is {}", getLeader().ip, batch.size(),
                        processedCount, beatDatums.size(), datums.size());

                // update datum entry
                String url = buildUrl(remote.ip, API_GET);
                Map<String, String> queryParam = new HashMap<>(1);
                queryParam.put("keys", URLEncoder.encode(keys, "UTF-8"));
                HttpClient.asyncHttpGet(url, null, queryParam, new Callback<String>() {
                    @Override
                    public void onReceive(RestResult<String> result) {
                        if (!result.ok()) {
                            return;
                        }

                        List<JsonNode> datumList = JacksonUtils
                                .toObj(result.getData(), new TypeReference<List<JsonNode>>() {
                                });

                        for (JsonNode datumJson : datumList) {
                            Datum newDatum = null;
                            OPERATE_LOCK.lock();
                            try {

                                Datum oldDatum = getDatum(datumJson.get("key").asText());

                                if (oldDatum != null && datumJson.get("timestamp").asLong() <= oldDatum.timestamp
                                        .get()) {
                                    Loggers.RAFT
                                            .info("[NACOS-RAFT] timestamp is smaller than that of mine, key: {}, remote: {}, local: {}",
                                                    datumJson.get("key").asText(),
                                                    datumJson.get("timestamp").asLong(), oldDatum.timestamp);
                                    continue;
                                }

                                if (KeyBuilder.matchServiceMetaKey(datumJson.get("key").asText())) {
                                    Datum<Service> serviceDatum = new Datum<>();
                                    serviceDatum.key = datumJson.get("key").asText();
                                    serviceDatum.timestamp.set(datumJson.get("timestamp").asLong());
                                    serviceDatum.value = JacksonUtils
                                            .toObj(datumJson.get("value").toString(), Service.class);
                                    newDatum = serviceDatum;
                                }

                                if (KeyBuilder.matchInstanceListKey(datumJson.get("key").asText())) {
                                    Datum<Instances> instancesDatum = new Datum<>();
                                    instancesDatum.key = datumJson.get("key").asText();
                                    instancesDatum.timestamp.set(datumJson.get("timestamp").asLong());
                                    instancesDatum.value = JacksonUtils
                                            .toObj(datumJson.get("value").toString(), Instances.class);
                                    newDatum = instancesDatum;
                                }

                                if (newDatum == null || newDatum.value == null) {
                                    Loggers.RAFT.error("receive null datum: {}", datumJson);
                                    continue;
                                }

                                raftStore.write(newDatum);

                                datums.put(newDatum.key, newDatum);
                                notifier.notify(newDatum.key, DataOperation.CHANGE, newDatum.value);

                                local.resetLeaderDue();

                                if (local.term.get() + 100 > remote.term.get()) {
                                    getLeader().term.set(remote.term.get());
                                    local.term.set(getLeader().term.get());
                                } else {
                                    local.term.addAndGet(100);
                                }

                                raftStore.updateTerm(local.term.get());

                                Loggers.RAFT.info("data updated, key: {}, timestamp: {}, from {}, local term: {}",
                                        newDatum.key, newDatum.timestamp, JacksonUtils.toJson(remote), local.term);

                            } catch (Throwable e) {
                                Loggers.RAFT
                                        .error("[RAFT-BEAT] failed to sync datum from leader, datum: {}", newDatum,
                                                e);
                            } finally {
                                OPERATE_LOCK.unlock();
                            }
                        }
                        try {
                            TimeUnit.MILLISECONDS.sleep(200);
                        } catch (InterruptedException e) {
                            Loggers.RAFT.error("[RAFT-BEAT] Interrupted error ", e);
                        }
                        return;
                    }

                    @Override
                    public void onError(Throwable throwable) {
                        Loggers.RAFT.error("[RAFT-BEAT] failed to sync datum from leader", throwable);
                    }

                    @Override
                    public void onCancel() {

                    }

                });

                batch.clear();

            } catch (Exception e) {
                Loggers.RAFT.error("[NACOS-RAFT] failed to handle beat entry, key: {}", datumKey);
            }

        }

        List<String> deadKeys = new ArrayList<>();
        for (Map.Entry<String, Integer> entry : receivedKeysMap.entrySet()) {
            if (entry.getValue() == 0) {
                deadKeys.add(entry.getKey());
            }
        }
        //批量删除
        for (String deadKey : deadKeys) {
            try {
                deleteDatum(deadKey);
            } catch (Exception e) {
                Loggers.RAFT.error("[NACOS-RAFT] failed to remove entry, key={} {}", deadKey, e);
            }
        }

    }

    return local;
}

Nacos集群数据一致性(持久化实例CP模式Raft协议实现)

注册中心CAP架构剖析