nacos cp集群架构解析

nacos cp集群架构解析,第1张

nacos cp集群架构解析

1. cap与base原则详解

2. nacos & zk & eureka的cap架构横向对比

3. raft协议动态图解

4. nacos集群cp架构基于raft协议源码剖析

5. nacos集群cp架构的脑裂问题


1. cap架构

cap并不能同时满足, 通常只能满住ap或者cp

nacos通过改变服务的持久化方法, 即实现了cp(ephemeral = true), 也实现了ap(ephemeral), 默认是ap 

3. raft协议动态图解

Rafthttp://thesecretlivesofdata.com/raft/raft中的三种角色 : leader, candidate,follower

多个节点之间, 通过投票的方式来选取leader

在项目启动时, 多个节点都是处于休眠状态, 最先苏醒的节点先发起投票,  此时其他节点还没有苏醒, 会将票都投给该节点, 该节点就会变成leader, 如果有多个节点同时苏醒, 那么他们的获得的投票数会相同, 则所有节点重新进入休眠, 当选举出一个leader是, leader会向所有的follower发送心跳证明自己还活着,同时发送心跳时还会发送leader中的数据, 所有的follower根据leader发送过来的数据进行对比, 判断自己的数据是否都拥有, 如果多就删除, 如果少就去leader拉数据, 如果leader挂了之后, 剩余的follower会重新投票, 选取新的leader, leader选取成功后, 即使之前的leader恢复过来,那么他也是一个follower

选取流程 : 

 





这样就选出了一个leader, 所有的写 *** 作都是通过leader执行的, leader中写好之后, 会将数据同步到其他的follower中, 如果follower中超过半数数据同步成功, 则认为数据写入成功, 将写入成功的信息返回给客户端  接下来看一下图解的这个过程





 


 



通过两次提交的方式, 来保证数据的一致性 , 第一次将数据发送到follower节点, 节点返回一个ack

半数以上的节点返回了ack, 则进行第二次提交

raft就此结束, 接下来看一下nacos实现的源码

nacos源码实现 : 

 

  

到此为止, 我们已经讲解了nacos如果通过leader进行写数据, 将数据同步给follower, 

并且讲解了如何保证一半以上节点写入成功

接下来讲解一下nacos如果选取leader的源码 : 

查看RaftCore类的init()方法

 进入MasterElection()run方法

到此为止, leader选举完成

接下来看一下心跳是如何发送的, 进入 new HeartBeat()run方法

 到这里发送心跳完成

接下来看一下follower节点如何接受心跳 : 进入raftController类的beat()方法

    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();
        //判断发送心跳的节点是不是leader,不是则抛异常
        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                    .info("[RAFT] out of date beat, beat-from-term: {}, beat-to-term: {}, remote peer: {}, and leaderDueMs: {}",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;
        }
        //获取leader节点的所有key
        final JsonNode beatDatums = beat.get("datums");
        local.resetLeaderDue();
        local.resetHeartbeatDue();
        
        peers.makeLeader(remote);
        
        if (!switchDomain.isSendBeatonly()) {
            
            Map receivedKeysMap = new HashMap<>(datums.size());
            //获取本节点拥有的key的集合,将所有的key放入到map中
            //key : key集合, value : 魔法值0 代表这个key是本节点中有的, 接下来这个value值会在删除key时起作用
            for (Map.Entry entry : datums.entrySet()) {
                receivedKeysMap.put(entry.getKey(), 0);
            }
            
            // now check datums
            List batch = new ArrayList<>();
            
            int processedCount = 0;
            //遍历leader的所有key
            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();
                //如果leader和本节点都有的值, 对应的value为1
                receivedKeysMap.put(datumKey, 1);
                
                try {
                    if (datums.containsKey(datumKey) && datums.get(datumKey).timestamp.get() >= timestamp
                            && processedCount < beatDatums.size()) {
                        continue;
                    }
                    //batch中的数据就是leader节点包含,本节点不包含的key, 获取本届点中也包含但是时间戳小于leader节点的
                    //batch中的key就是本节点需要到leader中拉取的key
                    if (!(datums.containsKey(datumKey) && datums.get(datumKey).timestamp.get() >= timestamp)) {
                        batch.add(datumKey);
                    }
                    //如果比leader少一个key并不会试时去拉取, 到达一定数量时才回去拉取
                    if (batch.size() < 50 && processedCount < beatDatums.size()) {
                        continue;
                    }
                    //拼接所有缺失的key
                    String keys = StringUtils.join(batch, ",");
                    
                    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());
                    
                    //拼接leader的url, 去leader拉取数据
                    String url = buildUrl(remote.ip, API_GET);
                    Map queryParam = new HashMap<>(1);
                    //将上面的keys进行封装, 封装到queryParam中, queryParam作为请求的参数
                    queryParam.put("keys", URLEncoder.encode(keys, "UTF-8"));
                    HttpClient.asyncHttpGet(url, null, queryParam, new Callback() {
                        @Override
                        public void onReceive(RestResult result) {
                            if (!result.ok()) {
                                return;
                            }
                            
                            List datumList = JacksonUtils
                                    .toObj(result.getData(), new TypeReference>() {
                                    });
                            //本节点补充缺失的数据
                            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 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 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() {
                        
                        }
                        
                    });
                    //清空batch
                    batch.clear();
                    
                } catch (Exception e) {
                    Loggers.RAFT.error("[NACOS-RAFT] failed to handle beat entry, key: {}", datumKey);
                }
                
            }
            
            List deadKeys = new ArrayList<>();
            //如果value还有为0的, 则说明leader中没有这个key,而本节点中有这个key, 可能是leader中删除了, 则需要在本节点删除这个key
            for (Map.Entry entry : receivedKeysMap.entrySet()) {
                if (entry.getValue() == 0) {
                    deadKeys.add(entry.getKey());
                }
            }
            
            for (String deadKey : deadKeys) {
                try {
                    deleteDatum(deadKey);
                } catch (Exception e) {
                    Loggers.RAFT.error("[NACOS-RAFT] failed to remove entry, key={} {}", deadKey, e);
                }
            }
            
        }
        
        return local;
    }

 源码讲解完毕

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原文地址: http://outofmemory.cn/zaji/5672383.html

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