Raft通过当选的领导者达成共识。筏集群中的服务器是领导者或追随者，并且在选举的精确情况下可以是候选者（领导者不可用）。领导者负责将日志复制到关注者。它通过发送心跳消息定期通知追随者它的存在。每个跟随者都有一个超时（通常在150到300毫秒之间），它期望领导者的心跳。接收心跳时重置超时。如果没有收到心跳，则关注者将其状态更改为候选人并开始领导选举。

详见：Raft算法

二、Nacos中Raft部分源码

Nacos server在启动时，会通过RunningConfig.onApplicationEvent()方法调用RaftCore.init()方法。

init()

public static void init() throws Exception {
Loggers.RAFT.info("initializing Raft sub-system");
// 启动Notifier，轮询Datums，通知RaftListener
executor.submit(notifier);
// 获取Raft集群节点，更新到PeerSet中
peers.add(NamingProxy.getServers());
long start = System.currentTimeMillis();
// 从磁盘加载Datum和term数据进行数据恢复
RaftStore.load();
Loggers.RAFT.info("cache loaded, peer count: {}, datum count: {}, current term: {}",
peers.size(), datums.size(), peers.getTerm());
while (true) {
if (notifier.tasks.size() <= 0) {
break;
}
Thread.sleep(1000L);
System.out.println(notifier.tasks.size());
}
Loggers.RAFT.info("finish to load data from disk, cost: {} ms.", (System.currentTimeMillis() - start));
GlobalExecutor.register(new MasterElection()); // Leader选举
GlobalExecutor.register1(new HeartBeat()); // Raft心跳
GlobalExecutor.register(new AddressServerUpdater(), GlobalExecutor.ADDRESS_SERVER_UPDATE_INTERVAL_MS);
if (peers.size() > 0) {
if (lock.tryLock(INIT_LOCK_TIME_SECONDS, TimeUnit.SECONDS)) {
initialized = true;
lock.unlock();
}
} else {
throw new Exception("peers is empty.");
}
Loggers.RAFT.info("timer started: leader timeout ms: {}, heart-beat timeout ms: {}",
GlobalExecutor.LEADER_TIMEOUT_MS, GlobalExecutor.HEARTBEAT_INTERVAL_MS);
}

在init方法主要做了如下几件事：

1. 获取Raft集群节点 peers.add(NamingProxy.getServers());
2. Raft集群数据恢复 RaftStore.load();
3. Raft选举 GlobalExecutor.register(new MasterElection());
4. Raft心跳 GlobalExecutor.register(new HeartBeat());
5. Raft发布内容
6. Raft保证内容一致性

1. 获取Raft集群节点

NamingProxy.getServers()获取集群节点

NamingProxy.refreshSrvIfNeed()得到节点信息
返回List<String> servers

NamingProxy.refreshSrvIfNeed()得到节点信息

如果单机模式

则本主机的ip:port为Raft节点信息；

否则

调用下面的NamingProxy.refreshServerListFromDisk()获取Raft集群节点信息
获取到Raft集群节点信息之后(即ip:port列表)，更新NamingProxy的List<String> serverlistFromConfig属性和List<String> servers属性。

NamingProxy.refreshServerListFromDisk()获取集群节点信息

从磁盘或系统环境变量种读取Raft集群节点信息，即ip:port列表

2. Raft集群数据恢复

Nacos启动/重启时会从磁盘加载Datum和term数据进行数据恢复。

nacos server端启动后->RaftCore.init()方法->RaftStore.load()方法。

RaftStore.load()

从磁盘获取Datum数据：

将Datum放到RaftCore的ConcurrentMap<String, Datum> datums集合中，key为Datum的key；

将Datum和ApplyAction.CHANGE封装成Pair放到Notifier的tasks队列中，通知相关的RaftListener；
从META_FILE_NAME：<user.home>\nacos\raft\meta.properties获取任期term值(long值)：

调用RaftSet.setTerm(long term)方法更新Raft集群中每个节点的term值

3. Raft选举

GlobalExecutor.register(new MasterElection())注册选举定时任务

Nacos的Raft选举是通过MasterElection这个线程任务完成的。

更新候选节点的election timeout、heart timeout。
调用MasterElection.sendVote()进行投票。

public class MasterElection implements Runnable {
@Override
public void run() {
try {
if (!peers.isReady()) {
return;
}
RaftPeer local = peers.local();
local.leaderDueMs -= GlobalExecutor.TICK_PERIOD_MS;
if (local.leaderDueMs > 0) {
return;
}
// 重置选举超时时间，每次心跳以及收到数据包都会重置
local.resetLeaderDue();
local.resetHeartbeatDue();
// 发起选举
sendVote();
} catch (Exception e) {
Loggers.RAFT.warn("[RAFT] error while master election {}", e);
}
}
}

MasterElection.sendVote()发送定时任务

重置Raft集群数据：

leader置为null；所有Raft节点的voteFor字段置为null；

更新候选节点数据：

任期term自增1；(通过自增1制造和其它节点的term差异，避免所有节点term一样选举不出Leader)

候选节点的voteFor字段设置为自己；

state置为CANDIDATE；

候选节点向除自身之外的所有其它Raft节点的/v1/ns/raft/vote发送HTTP POST请求：

请求内容为vote:JSON.toJSONString(local)

候选节点收到其他节点投的候选节点数据，交给PeerSet.decideLeader()方法处理

把超半数的voteFor对应的RaftPerr设置为Leader。

public void sendVote() {
RaftPeer local = peers.get(NetUtils.localServer());
Loggers.RAFT.info("leader timeout, start voting,leader: {}, term: {}",
JSON.toJSONString(getLeader()), local.term);
//重置Raft集群数据
peers.reset();
//更新候选节点数据
local.term.incrementAndGet();
local.voteFor = local.ip;
local.state = RaftPeer.State.CANDIDATE;
//候选节点向除自身之外的所有其它Raft节点的/v1/ns/raft/vote发送HTTP POST请求
//请求内容为vote:JSON.toJSONString(local)
Map<String, String> params = new HashMap<String, String>(1);
params.put("vote", JSON.toJSONString(local));
for (final String server : peers.allServersWithoutMySelf()) {
final String url = buildURL(server, API_VOTE);
try {
HttpClient.asyncHttpPost(url, null, params, new AsyncCompletionHandler<Integer>() {
@Override
public Integer onCompleted(Response response) throws Exception {
if (response.getStatusCode() != HttpURLConnection.HTTP_OK) {
Loggers.RAFT.error("NACOS-RAFT vote failed: {}, url: {}", response.getResponseBody(), url);
return 1;
}
RaftPeer peer = JSON.parseObject(response.getResponseBody(), RaftPeer.class);
Loggers.RAFT.info("received approve from peer: {}", JSON.toJSONString(peer));
//候选节点收到其他节点投的候选节点数据，交给PeerSet.decideLeader
//方法处理
peers.decideLeader(peer);
return 0;
}
});
} catch (Exception e) {
Loggers.RAFT.warn("error while sending vote to server: {}", server);
}
}
}
}

（1）RaftCommands.vote()处理/v1/ns/raft/vote请求

选举请求的 http 接口

@RestController
@RequestMapping(UtilsAndCommons.NACOS_NAMING_CONTEXT + "/raft")
public class RaftController {
......
@NeedAuth
@RequestMapping(value = "/vote", method = RequestMethod.POST)
public JSONObject vote(HttpServletRequest request, HttpServletResponse response) throws Exception {
// 处理选举请求
RaftPeer peer = raftCore.receivedVote(
JSON.parseObject(WebUtils.required(request, "vote"), RaftPeer.class));
return JSON.parseObject(JSON.toJSONString(peer));
}
......
}

调用RaftCore.MasterElection.receivedVote()方法

如果收到的候选节点term比本地节点term要小，则：

本地节点的voteFor更新为自己；(意思是我自己更适合做leader，这一票我投给自己)

否则：

这个Follower重置它的election timeout；

更新它的voteFor为收到的候选节点ip；(意思是就按你说的做，这一票就投给你了。)

更新它的term为收到的候选节点term；

将本地节点作为http响应返回；

@Component
public class RaftCore {
......
public RaftPeer receivedVote(RaftPeer remote) {
if (!peers.contains(remote)) {
throw new IllegalStateException("can not find peer: " + remote.ip);
}
// 若当前节点的 term 大于等于发送选举请求的节点 term，则选择自己为 leader
RaftPeer local = peers.get(NetUtils.localServer());
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;
}
local.resetLeaderDue();
// 若当前节点的 term 小于发送请求的节点 term，选择发送请求的节点为 leader
local.state = RaftPeer.State.FOLLOWER;
local.voteFor = remote.ip;
local.term.set(remote.term.get());
Loggers.RAFT.info("vote {} as leader, term: {}", remote.ip, remote.term);
return local;
}
}

（2）PeerSet.decideLeader()选举

@Component
@DependsOn("serverListManager")
public class RaftPeerSet implements ServerChangeListener {
......
public RaftPeer decideLeader(RaftPeer candidate) {
peers.put(candidate.ip, candidate);
SortedBag ips = new TreeBag();
int maxApproveCount = 0;
String maxApprovePeer = null;
// 遍历所有的节点，若 voteFor 不为空，则将节点的 voteFor 添加到 ips 中，记录被选举次数最多的节点和次数
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;
}
}
// 将选举出来的节点设置为 leader
if (maxApproveCount >= majorityCount()) {
RaftPeer peer = peers.get(maxApprovePeer);
peer.state = RaftPeer.State.LEADER;
if (!Objects.equals(leader, peer)) {
leader = peer;
Loggers.RAFT.info("{} has become the LEADER", leader.ip);
}
}
return leader;
}
}

4. Raft心跳

GlobalExecutor.register(new HeartBeat())注册心跳定时任务

重置Leader节点的heart timeout、election timeout；
sendBeat()发送心跳包

public class HeartBeat implements Runnable {
@Override
public void run() {
try {
if (!peers.isReady()) {
return;
}
RaftPeer local = peers.local();
// hearbeatDueMs 默认为 5s，TICK_PERIOD_MS 为 500ms，每 500ms 检查一次，每 5s 发送一次心跳
local.heartbeatDueMs -= GlobalExecutor.TICK_PERIOD_MS;
if (local.heartbeatDueMs > 0) {
return;
}
// 重置 heartbeatDueMs
local.resetHeartbeatDue();
// 发送心跳包
sendBeat();
} catch (Exception e) {
Loggers.RAFT.warn("[RAFT] error while sending beat {}", e);
}
}
}

HeartBeat.sendBeat()发送心跳包

重置Leader节点的heart timeout、election timeout；
向除自身之外的其它节点/v1/ns/raft/beat路径发送HTTP POST请求，请求内容如下：

JSONObject packet = new JSONObject();

packet.put("peer", local); //local为Leader节点对应的RaftPeer对象

packet.put("datums", array); //array中封装了RaftCore中所有的Datum的key和timestamp

Map<String, String> params = new HashMap<String, String>(1);

params.put("beat", JSON.toJSONString(packet));

拿到各个节点返回的http响应，即RaftPeer对象，更新PeerSet的Map<String, RaftPeer> peers集合。(保持集群节点数据一致)

public void sendBeat() throws IOException, InterruptedException {
RaftPeer local = peers.local();
// 只有 leader 才发送心跳
if (local.state != RaftPeer.State.LEADER && !STANDALONE_MODE) {
return;
}
Loggers.RAFT.info("[RAFT] send beat with {} keys.", datums.size());
// 重置收不到包就选举 leader 的时间间隔
local.resetLeaderDue();
// 构建心跳包信息，local 为当前 nacos 节点的信息，key 为 peer
JSONObject packet = new JSONObject();
packet.put("peer", local);
JSONArray array = new JSONArray();
// 只发送心跳包，不带数据过去
if (switchDomain.isSendBeatOnly()) {
Loggers.RAFT.info("[SEND-BEAT-ONLY] {}", String.valueOf(switchDomain.isSendBeatOnly()));
}
// 将相关的 key 通过心跳包发送给 follower
if (!switchDomain.isSendBeatOnly()) {
for (Datum datum : datums.values()) {
JSONObject element = new JSONObject();
// 将 key 和对应的版本放入 element 中，最终添加到 array 里
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));
}
element.put("timestamp", datum.timestamp);
array.add(element);
}
} else {
Loggers.RAFT.info("[RAFT] send beat only.");
}
// 将所有 key 组成的 array 放入数据包
packet.put("datums", array);
// 将数据包转换成 json 字符串放入 params 中
Map<String, String> params = new HashMap<String, String>(1);
params.put("beat", JSON.toJSONString(packet));
String content = JSON.toJSONString(params);
// 用 gzip 压缩
ByteArrayOutputStream out = new ByteArrayOutputStream();
GZIPOutputStream gzip = new GZIPOutputStream(out);
gzip.write(content.getBytes("UTF-8"));
gzip.close();
byte[] compressedBytes = out.toByteArray();
String compressedContent = new String(compressedBytes, "UTF-8");
Loggers.RAFT.info("raw beat data size: {}, size of compressed data: {}",
content.length(), compressedContent.length());
// 将心跳包发送给所有的 follower
for (final String server : peers.allServersWithoutMySelf()) {
try {
final String url = buildURL(server, API_BEAT);
Loggers.RAFT.info("send beat to server " + server);
HttpClient.asyncHttpPostLarge(url, null, compressedBytes, new AsyncCompletionHandler<Integer>() {
@Override
public Integer onCompleted(Response response) throws Exception {
if (response.getStatusCode() != HttpURLConnection.HTTP_OK) {
Loggers.RAFT.error("NACOS-RAFT beat failed: {}, peer: {}",
response.getResponseBody(), server);
MetricsMonitor.getLeaderSendBeatFailedException().increment();
return 1;
}
peers.update(JSON.parseObject(response.getResponseBody(), RaftPeer.class));
Loggers.RAFT.info("receive beat response from: {}", url);
return 0;
}
@Override
public void onThrowable(Throwable t) {
Loggers.RAFT.error("NACOS-RAFT error while sending heart-beat to peer: {} {}", server, t);
MetricsMonitor.getLeaderSendBeatFailedException().increment();
}
});
} catch (Exception e) {
Loggers.RAFT.error("error while sending heart-beat to peer: {} {}", server, e);
MetricsMonitor.getLeaderSendBeatFailedException().increment();
}
}
}

（·）RaftCommands.beat()方法处理/v1/ns/raft/beat请求

接收心跳包的 http 接口：

@RestController
@RequestMapping(UtilsAndCommons.NACOS_NAMING_CONTEXT + "/raft")
public class RaftController {
......
@NeedAuth
@RequestMapping(value = "/beat", method = RequestMethod.POST)
public JSONObject beat(HttpServletRequest request, HttpServletResponse response) throws Exception {
String entity = new String(IoUtils.tryDecompress(request.getInputStream()), "UTF-8");
String value = URLDecoder.decode(entity, "UTF-8");
value = URLDecoder.decode(value, "UTF-8");
// 解析心跳包
JSONObject json = JSON.parseObject(value);
JSONObject beat = JSON.parseObject(json.getString("beat"));
// 处理心跳包并将本节点的信息作为 response 返回
RaftPeer peer = raftCore.receivedBeat(beat);
return JSON.parseObject(JSON.toJSONString(peer));
}
......
}

HeartBeat.receivedBeat()处理心跳包

如果收到心跳的节点不是Follower角色，则设置为Follower角色，并把它的voteFor设置为Leader节点的ip；
重置本地节点的heart timeout、election timeout；
调用PeerSet.makeLeader()通知这个节点更新Leader；(也就是说Leader节点会通过心跳通知其它节点更新Leader)
检查Datum：

遍历请求参数中的datums，如果Follwoer不存在这个datumKey或者时间戳比较旧，则收集这个datumKey；

每收集到50个datumKey，则向Leader节点的/v1/ns/raft/get路径发送请求，请求参数为这50个datumKey，获取对应的50个最新的Datum对象；

遍历这些Daum对象，接下来做的是和RaftCore.onPublish()方法中做的事类似：
1.调用RaftStore#write将Datum序列化为json写到cacheFile中
2.将Datum存放到RaftCore的datums集合中，key为上面的datum的key值
3.更新本地节点的election timeout
4.更新本地节点的任期term
5.本地节点的任期term持久化到properties文件中
6.调用notifier.addTask(datum, Notifier.ApplyAction.CHANGE);

通知对应的RaftListener

RaftCore.deleteDatum(String key)用来删除旧的Datum
datums集合中删除key对应的Datum；
RaftStore.delete()，在磁盘上删除这个Datum对应的文件；
notifier.addTask(deleted, Notifier.ApplyAction.DELETE)，通知对应的RaftListener有DELETE事件。

本地节点的RaftPeer作为http响应返回。

@Component
public class RaftCore {
......
public RaftPeer receivedBeat(JSONObject beat) throws Exception {
final RaftPeer local = peers.local();
// 解析发送心跳包的节点信息
final RaftPeer remote = new RaftPeer();
remote.ip = beat.getJSONObject("peer").getString("ip");
remote.state = RaftPeer.State.valueOf(beat.getJSONObject("peer").getString("state"));
remote.term.set(beat.getJSONObject("peer").getLongValue("term"));
remote.heartbeatDueMs = beat.getJSONObject("peer").getLongValue("heartbeatDueMs");
remote.leaderDueMs = beat.getJSONObject("peer").getLongValue("leaderDueMs");
remote.voteFor = beat.getJSONObject("peer").getString("voteFor");
// 若收到的心跳包不是 leader 节点发送的，则抛异常
if (remote.state != RaftPeer.State.LEADER) {
Loggers.RAFT.info("[RAFT] invalid state from master, state: {}, remote peer: {}",
remote.state, JSON.toJSONString(remote));
throw new IllegalArgumentException("invalid state from master, state: " + remote.state);
}
// 本地 term 大于心跳包的 term，则心跳包不进行处理
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(), JSON.toJSONString(remote), local.leaderDueMs);
throw new IllegalArgumentException("out of date beat, beat-from-term: " + remote.term.get()
+ ", beat-to-term: " + local.term.get());
}
// 若当前节点不是 follower 节点，则将其更新为 follower 节点
if (local.state != RaftPeer.State.FOLLOWER) {
Loggers.RAFT.info("[RAFT] make remote as leader, remote peer: {}", JSON.toJSONString(remote));
// mk follower
local.state = RaftPeer.State.FOLLOWER;
local.voteFor = remote.ip;
}
final JSONArray beatDatums = beat.getJSONArray("datums");
// 更新心跳包发送间隔和收不到心跳包的选举间隔
local.resetLeaderDue();
local.resetHeartbeatDue();
// 更新 leader 信息，将 remote 设置为新 leader，更新原有 leader 的节点信息
peers.makeLeader(remote);
// 将当前节点的 key 存放到一个 map 中，value 都为 0
Map<String, Integer> receivedKeysMap = new HashMap<String, Integer>(datums.size());
for (Map.Entry<String, Datum> entry : datums.entrySet()) {
receivedKeysMap.put(entry.getKey(), 0);
}
// 检查接收到的 datum 列表
List<String> batch = new ArrayList<String>();
if (!switchDomain.isSendBeatOnly()) {
int processedCount = 0;
Loggers.RAFT.info("[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;
JSONObject entry = (JSONObject) object;
String key = entry.getString("key");
final String datumKey;
// 构建 datumKey（加上前缀，发送的时候 key 是去掉了前缀的）
if (KeyBuilder.matchServiceMetaKey(key)) {
datumKey = KeyBuilder.detailServiceMetaKey(key);
} else if (KeyBuilder.matchInstanceListKey(key)) {
datumKey = KeyBuilder.detailInstanceListkey(key);
} else {
// ignore corrupted key:
continue;
}
// 获取收到的 key 对应的版本
long timestamp = entry.getLong("timestamp");
// 将收到的 key 在本地 key 的 map 中标记为 1
receivedKeysMap.put(datumKey, 1);
try {
// 收到的 key 在本地存在并且本地的版本大于收到的版本并且还有数据未处理，则直接 continue
if (datums.containsKey(datumKey) && datums.get(datumKey).timestamp.get() >= timestamp && processedCount < beatDatums.size()) {
continue;
}
// 若收到的 key 在本地没有，或者本地的版本小于收到的版本，放入 batch，准备下一步获取数据
if (!(datums.containsKey(datumKey) && datums.get(datumKey).timestamp.get() >= timestamp)) {
batch.add(datumKey);
}
// 只有 batch 的数量超过 50 或已经处理完了，才进行获取数据操作
if (batch.size() < 50 && processedCount < beatDatums.size()) {
continue;
}
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());
// 获取对应 key 的数据
// update datum entry
String url = buildURL(remote.ip, API_GET) + "?keys=" + URLEncoder.encode(keys, "UTF-8");
HttpClient.asyncHttpGet(url, null, null, new AsyncCompletionHandler<Integer>() {
@Override
public Integer onCompleted(Response response) throws Exception {
if (response.getStatusCode() != HttpURLConnection.HTTP_OK) {
return 1;
}
List<Datum> datumList = JSON.parseObject(response.getResponseBody(), new TypeReference<List<Datum>>() {
});
// 更新本地数据
for (Datum datum : datumList) {
OPERATE_LOCK.lock();
try {
Datum oldDatum = getDatum(datum.key);
if (oldDatum != null && datum.timestamp.get() <= oldDatum.timestamp.get()) {
Loggers.RAFT.info("[NACOS-RAFT] timestamp is smaller than that of mine, key: {}, remote: {}, local: {}",
datum.key, datum.timestamp, oldDatum.timestamp);
continue;
}
raftStore.write(datum);
if (KeyBuilder.matchServiceMetaKey(datum.key)) {
Datum<Service> serviceDatum = new Datum<>();
serviceDatum.key = datum.key;
serviceDatum.timestamp.set(datum.timestamp.get());
serviceDatum.value = JSON.parseObject(JSON.toJSONString(datum.value), Service.class);
datum = serviceDatum;
}
if (KeyBuilder.matchInstanceListKey(datum.key)) {
Datum<Instances> instancesDatum = new Datum<>();
instancesDatum.key = datum.key;
instancesDatum.timestamp.set(datum.timestamp.get());
instancesDatum.value = JSON.parseObject(JSON.toJSONString(datum.value), Instances.class);
datum = instancesDatum;
}
datums.put(datum.key, datum);
notifier.addTask(datum.key, ApplyAction.CHANGE);
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: {}",
datum.key, datum.timestamp, JSON.toJSONString(remote), local.term);
} catch (Throwable e) {
Loggers.RAFT.error("[RAFT-BEAT] failed to sync datum from leader, key: {} {}", datum.key, e);
} finally {
OPERATE_LOCK.unlock();
}
}
TimeUnit.MILLISECONDS.sleep(200);
return 0;
}
});
batch.clear();
} catch (Exception e) {
Loggers.RAFT.error("[NACOS-RAFT] failed to handle beat entry, key: {}", datumKey);
}
}
// 若某个 key 在本地存在但收到的 key 列表中没有，则证明 leader 已经删除，那么本地也要删除
List<String> deadKeys = new ArrayList<String>();
for (Map.Entry<String, Integer> 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;
}
}

5. Raft发布内容

注册入口

注册http接口

@RestController
@RequestMapping(UtilsAndCommons.NACOS_NAMING_CONTEXT + "/instance")
public class InstanceController {
......
@CanDistro
@RequestMapping(value = "", method = RequestMethod.POST)
public String register(HttpServletRequest request) throws Exception {
// 获取 namespace 和 serviceName
String serviceName = WebUtils.required(request, CommonParams.SERVICE_NAME);
String namespaceId = WebUtils.optional(request, CommonParams.NAMESPACE_ID, Constants.DEFAULT_NAMESPACE_ID);
// 执行注册逻辑
serviceManager.registerInstance(namespaceId, serviceName, parseInstance(request));
return "ok";
}
}

注册实例

@Component
@DependsOn("nacosApplicationContext")
public class ServiceManager implements RecordListener<Service> {
......
private Map<String, Map<String, Service>> serviceMap = new ConcurrentHashMap<>();
......
// 注册新实例
public void registerInstance(String namespaceId, String serviceName, Instance instance) throws NacosException {
// 创建空 service，所有的 service 都存放在 serviceMap 中，serviceMap 类型为：Map<String, Map<String, Service>>，第一层 map 的 key 为 namespace，第二层 map 的 key 为 serviceName；
// 每个 service 中维护一个 clusterMap，clusterMap 中有两个 set，用来存放 instance
if (ServerMode.AP.name().equals(switchDomain.getServerMode())) {
createEmptyService(namespaceId, serviceName);
}
Service service = getService(namespaceId, serviceName);
if (service == null) {
throw new NacosException(NacosException.INVALID_PARAM,
"service not found, namespace: " + namespaceId + ", service: " + serviceName);
}
// 检查实例是否已存在，通过 ip 进行比较
if (service.allIPs().contains(instance)) {
throw new NacosException(NacosException.INVALID_PARAM, "instance already exist: " + instance);
}
// 添加新实例
addInstance(namespaceId, serviceName, instance.isEphemeral(), instance);
}
// 创建空 service
public void createEmptyService(String namespaceId, String serviceName) throws NacosException {
Service service = getService(namespaceId, serviceName);
if (service == null) {
service = new Service();
service.setName(serviceName);
service.setNamespaceId(namespaceId);
service.setGroupName(Constants.DEFAULT_GROUP);
// now validate the service. if failed, exception will be thrown
service.setLastModifiedMillis(System.currentTimeMillis());
service.recalculateChecksum();
service.validate();
putService(service);
service.init();
// 添加对 service 的监听，用来同步数据
consistencyService.listen(KeyBuilder.buildInstanceListKey(service.getNamespaceId(), service.getName(), true), service);
consistencyService.listen(KeyBuilder.buildInstanceListKey(service.getNamespaceId(), service.getName(), false), service);
}
}
// 添加 instance 到缓存中，并且持久化
public void addInstance(String namespaceId, String serviceName, boolean ephemeral, Instance... ips) throws NacosException {
String key = KeyBuilder.buildInstanceListKey(namespaceId, serviceName, ephemeral);
Service service = getService(namespaceId, serviceName);
// 添加 instance 到本地缓存
List<Instance> instanceList = addIpAddresses(service, ephemeral, ips);
Instances instances = new Instances();
instances.setInstanceList(instanceList);
// 将 instance 信息持久化
consistencyService.put(key, instances);
}
// 添加实例到缓存
public List<Instance> addIpAddresses(Service service, boolean ephemeral, Instance... ips) throws NacosException {
return updateIpAddresses(service, UtilsAndCommons.UPDATE_INSTANCE_ACTION_ADD, ephemeral, ips);
}
// 真正的添加实例到缓存的逻辑
public List<Instance> updateIpAddresses(Service service, String action, boolean ephemeral, Instance... ips) throws NacosException {
Datum datum = consistencyService.get(KeyBuilder.buildInstanceListKey(service.getNamespaceId(), service.getName(), ephemeral));
Map<String, Instance> oldInstanceMap = new HashMap<>(16);
List<Instance> currentIPs = service.allIPs(ephemeral);
Map<String, Instance> map = new ConcurrentHashMap<>(currentIPs.size());
for (Instance instance : currentIPs) {
map.put(instance.toIPAddr(), instance);
}
if (datum != null) {
oldInstanceMap = setValid(((Instances) datum.value).getInstanceList(), map);
}
// use HashMap for deep copy:
HashMap<String, Instance> instanceMap = new HashMap<>(oldInstanceMap.size());
instanceMap.putAll(oldInstanceMap);
for (Instance instance : ips) {
if (!service.getClusterMap().containsKey(instance.getClusterName())) {
Cluster cluster = new Cluster(instance.getClusterName());
cluster.setService(service);
service.getClusterMap().put(instance.getClusterName(), cluster);
Loggers.SRV_LOG.warn("cluster: {} not found, ip: {}, will create new cluster with default configuration.",
instance.getClusterName(), instance.toJSON());
}
if (UtilsAndCommons.UPDATE_INSTANCE_ACTION_REMOVE.equals(action)) {
instanceMap.remove(instance.getDatumKey());
} else {
instanceMap.put(instance.getDatumKey(), instance);
}
}
if (instanceMap.size() <= 0 && UtilsAndCommons.UPDATE_INSTANCE_ACTION_ADD.equals(action)) {
throw new IllegalArgumentException("ip list can not be empty, service: " + service.getName() + ", ip list: "
+ JSON.toJSONString(instanceMap.values()));
}
return new ArrayList<>(instanceMap.values());
}
// 将旧的 instance 列表与新的 instance 合并到一起
private Map<String, Instance> setValid(List<Instance> oldInstances, Map<String, Instance> map) {
Map<String, Instance> instanceMap = new HashMap<>(oldInstances.size());
for (Instance instance : oldInstances) {
Instance instance1 = map.get(instance.toIPAddr());
if (instance1 != null) {
instance.setHealthy(instance1.isHealthy());
instance.setLastBeat(instance1.getLastBeat());
}
instanceMap.put(instance.getDatumKey(), instance);
}
return instanceMap;
}
......
}

实例信息持久化

RaftConsistencyServiceImpl.put() 方法用来做实例信息持久化的工作，即上面提到的consistencyService.put(key, instances);这一步

（1）Service.put()

@Service
public class RaftConsistencyServiceImpl implements PersistentConsistencyService {
......
@Override
public void put(String key, Record value) throws NacosException {
try {
raftCore.signalPublish(key, value);
} catch (Exception e) {
Loggers.RAFT.error("Raft put failed.", e);
throw new NacosException(NacosException.SERVER_ERROR, "Raft put failed, key:" + key + ", value:" + value);
}
}
}

最终调用到 RaftCore 的 signalPublish() 方法：

（2）RaftCore.signalPublish()

@Component
public class RaftCore {
......
public void signalPublish(String key, Record value) throws Exception {
// 若不是 leader，直接将包转发给 leader
if (!isLeader()) {
JSONObject params = new JSONObject();
params.put("key", key);
params.put("value", value);
Map<String, String> parameters = new HashMap<>(1);
parameters.put("key", key);
// 调用 /raft/datum 接口
raftProxy.proxyPostLarge(getLeader().ip, API_PUB, params.toJSONString(), parameters);
return;
}
// 若是 leader，将包发送给所有的 follower
try {
OPERATE_LOCK.lock();
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());
}
JSONObject json = new JSONObject();
json.put("datum", datum);
json.put("source", peers.local());
// 本地 onPublish 方法用来处理持久化逻辑
onPublish(datum, peers.local());
final String content = JSON.toJSONString(json);
final CountDownLatch latch = new CountDownLatch(peers.majorityCount());
// 将包发送给所有的 follower，调用 /raft/datum/commit 接口
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 AsyncCompletionHandler<Integer>() {
@Override
public Integer onCompleted(Response response) throws Exception {
if (response.getStatusCode() != HttpURLConnection.HTTP_OK) {
Loggers.RAFT.warn("[RAFT] failed to publish data to peer, datumId={}, peer={}, http code={}",
datum.key, server, response.getStatusCode());
return 1;
}
latch.countDown();
return 0;
}
@Override
public STATE onContentWriteCompleted() {
return STATE.CONTINUE;
}
});
}
if (!latch.await(UtilsAndCommons.RAFT_PUBLISH_TIMEOUT, TimeUnit.MILLISECONDS)) {
// only majority servers return success can we consider this update success
Loggers.RAFT.info("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();
}
}
}

（3）/raft/datum 接口和 /raft/datum/commit 接口

@RestController
@RequestMapping(UtilsAndCommons.NACOS_NAMING_CONTEXT + "/raft")
public class RaftController {
......
@NeedAuth
@RequestMapping(value = "/datum", method = RequestMethod.POST)
public String publish(HttpServletRequest request, HttpServletResponse response) throws Exception {
response.setHeader("Content-Type", "application/json; charset=" + getAcceptEncoding(request));
response.setHeader("Cache-Control", "no-cache");
response.setHeader("Content-Encode", "gzip");
String entity = IOUtils.toString(request.getInputStream(), "UTF-8");
String value = URLDecoder.decode(entity, "UTF-8");
JSONObject json = JSON.parseObject(value);
// 这里也是调用 RaftConsistencyServiceImpl.put() 进行处理，与服务注册的逻辑在此回合，最终调用到 signalPublish 方法
String key = json.getString("key");
if (KeyBuilder.matchInstanceListKey(key)) {
raftConsistencyService.put(key, JSON.parseObject(json.getString("value"), Instances.class));
return "ok";
}
if (KeyBuilder.matchSwitchKey(key)) {
raftConsistencyService.put(key, JSON.parseObject(json.getString("value"), SwitchDomain.class));
return "ok";
}
if (KeyBuilder.matchServiceMetaKey(key)) {
raftConsistencyService.put(key, JSON.parseObject(json.getString("value"), Service.class));
return "ok";
}
throw new NacosException(NacosException.INVALID_PARAM, "unknown type publish key: " + key);
}
@NeedAuth
@RequestMapping(value = "/datum/commit", method = RequestMethod.POST)
public String onPublish(HttpServletRequest request, HttpServletResponse response) throws Exception {
response.setHeader("Content-Type", "application/json; charset=" + getAcceptEncoding(request));
response.setHeader("Cache-Control", "no-cache");
response.setHeader("Content-Encode", "gzip");
String entity = IOUtils.toString(request.getInputStream(), "UTF-8");
String value = URLDecoder.decode(entity, "UTF-8");
JSONObject jsonObject = JSON.parseObject(value);
String key = "key";
RaftPeer source = JSON.parseObject(jsonObject.getString("source"), RaftPeer.class);
JSONObject datumJson = jsonObject.getJSONObject("datum");
Datum datum = null;
if (KeyBuilder.matchInstanceListKey(datumJson.getString(key))) {
datum = JSON.parseObject(jsonObject.getString("datum"), new TypeReference<Datum<Instances>>() {});
} else if (KeyBuilder.matchSwitchKey(datumJson.getString(key))) {
datum = JSON.parseObject(jsonObject.getString("datum"), new TypeReference<Datum<SwitchDomain>>() {});
} else if (KeyBuilder.matchServiceMetaKey(datumJson.getString(key))) {
datum = JSON.parseObject(jsonObject.getString("datum"), new TypeReference<Datum<Service>>() {});
}
// 该方法最终调用到 onPublish 方法
raftConsistencyService.onPut(datum, source);
return "ok";
}
......
}

发布入口 RaftCommands.publish()

@Component
public class RaftCore {
......
public void onPublish(Datum datum, RaftPeer source) throws Exception {
RaftPeer local = peers.local();
if (datum.value == null) {
Loggers.RAFT.warn("received empty datum");
throw new IllegalStateException("received empty datum");
}
// 若该包不是 leader 发布来的，抛异常
if (!peers.isLeader(source.ip)) {
Loggers.RAFT.warn("peer {} tried to publish data but wasn't leader, leader: {}",
JSON.toJSONString(source), JSON.toJSONString(getLeader()));
throw new IllegalStateException("peer(" + source.ip + ") tried to publish " +
"data but wasn't leader");
}
// 来源 term 小于本地当前 term，抛异常
if (source.term.get() < local.term.get()) {
Loggers.RAFT.warn("out of date publish, pub-term: {}, cur-term: {}",
JSON.toJSONString(source), JSON.toJSONString(local));
throw new IllegalStateException("out of date publish, pub-term:"
+ source.term.get() + ", cur-term: " + local.term.get());
}
// 更新选举超时时间
local.resetLeaderDue();
// 节点信息持久化
// if data should be persistent, usually this is always true:
if (KeyBuilder.matchPersistentKey(datum.key)) {
raftStore.write(datum);
}
// 添加到缓存
datums.put(datum.key, datum);
// 更新 term 信息
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());
// 通知应用程序节点信息有变动
notifier.addTask(datum.key, ApplyAction.CHANGE);
Loggers.RAFT.info("data added/updated, key={}, term={}", datum.key, local.term);
}
}

6. Raft保证内容一致性

Nacos通过Raft发布内容，内容只是存在了Leader节点上，通过Raft心跳机制来保证一致性。

在注册信息的时候，addInstance() 方法将 instance 添加到了本地缓存中，但 raft 在从 leader 到 follower 同步数据的时候，follower 接收到包之后，只是通过 onPublish() 方法进行了持久化，并没有将信息更新到本地缓存，而是通过一个监听器来实现：

在 onPublish 方法最后，有一行：notifier.addTask(datum.key, ApplyAction.CHANGE);，即：将本次的变动，添加到通知任务中，我们来看通知任务将如何被处理：

@Component
public class RaftCore {
......
public class Notifier implements Runnable {
private ConcurrentHashMap<String, String> services = new ConcurrentHashMap<>(10 * 1024);
private BlockingQueue<Pair> tasks = new LinkedBlockingQueue<Pair>(1024 * 1024);
// 添加变更任务到 tasks 队列
public void addTask(String datumKey, ApplyAction action) {
if (services.containsKey(datumKey) && action == ApplyAction.CHANGE) {
return;
}
if (action == ApplyAction.CHANGE) {
services.put(datumKey, StringUtils.EMPTY);
}
tasks.add(Pair.with(datumKey, action));
}
public int getTaskSize() {
return tasks.size();
}
// 处理任务线程
@Override
public void run() {
Loggers.RAFT.info("raft notifier started");
while (true) {
try {
Pair pair = tasks.take();
if (pair == null) {
continue;
}
String datumKey = (String) pair.getValue0();
ApplyAction action = (ApplyAction) pair.getValue1();
// 从服务列表中删除该 key
services.remove(datumKey);
int count = 0;
if (listeners.containsKey(KeyBuilder.SERVICE_META_KEY_PREFIX)) {
if (KeyBuilder.matchServiceMetaKey(datumKey) && !KeyBuilder.matchSwitchKey(datumKey)) {
for (RecordListener listener : listeners.get(KeyBuilder.SERVICE_META_KEY_PREFIX)) {
try {
// 根据变更类型，调用不同的回调方法来进行缓存更新
if (action == ApplyAction.CHANGE) {
listener.onChange(datumKey, getDatum(datumKey).value);
}
if (action == ApplyAction.DELETE) {
listener.onDelete(datumKey);
}
} catch (Throwable e) {
Loggers.RAFT.error("[NACOS-RAFT] error while notifying listener of key: {} {}", datumKey, e);
}
}
}
}
if (!listeners.containsKey(datumKey)) {
continue;
}
for (RecordListener listener : listeners.get(datumKey)) {
count++;
try {
if (action == ApplyAction.CHANGE) {
listener.onChange(datumKey, getDatum(datumKey).value);
continue;
}
if (action == ApplyAction.DELETE) {
listener.onDelete(datumKey);
continue;
}
} catch (Throwable e) {
Loggers.RAFT.error("[NACOS-RAFT] error while notifying listener of key: {} {}", datumKey, e);
}
}
if (Loggers.RAFT.isDebugEnabled()) {
Loggers.RAFT.debug("[NACOS-RAFT] datum change notified, key: {}, listener count: {}", datumKey, count);
}
} catch (Throwable e) {
Loggers.RAFT.error("[NACOS-RAFT] Error while handling notifying task", e);
}
}
}
}
}

码农公寓

Nacos数据一致性

一、Raft算法