Spring Cloud Eureka 全解 （3） - 核心流程-服务注册与取消详解
Spring Cloud Eureka 全解 （3） - 核心流程-服务注册与取消详解
干货满满张哈希
发布于 2021-04-12 15:36:26
发布于 2021-04-12 15:36:26
关于服务注册
开启/关闭服务注册配置：eureka.client.register-with-eureka = true （默认）
什么时候注册？
- 应用第一次启动时，初始化EurekaClient时，应用状态改变：从STARTING变为UP会触发这个Listener，调用instanceInfoReplicator.onDemandUpdate(); 可以推测出，实例状态改变时，也会通过注册接口更新实例状态信息
statusChangeListener = new ApplicationInfoManager.StatusChangeListener() {
@Override
public String getId() {
return "statusChangeListener";
}
@Override
public void notify(StatusChangeEvent statusChangeEvent) {
if (InstanceStatus.DOWN == statusChangeEvent.getStatus() ||
InstanceStatus.DOWN == statusChangeEvent.getPreviousStatus()) {
// log at warn level if DOWN was involved
logger.warn("Saw local status change event {}", statusChangeEvent);
} else {
logger.info("Saw local status change event {}", statusChangeEvent);
}
instanceInfoReplicator.onDemandUpdate();
}
};- 定时任务，如果InstanceInfo发生改变，也会通过注册接口更新信息
public void run() {
try {
discoveryClient.refreshInstanceInfo();
//如果实例信息发生改变，则需要调用register更新InstanceInfo
Long dirtyTimestamp = instanceInfo.isDirtyWithTime();
if (dirtyTimestamp != null) {
discoveryClient.register();
instanceInfo.unsetIsDirty(dirtyTimestamp);
}
} catch (Throwable t) {
logger.warn("There was a problem with the instance info replicator", t);
} finally {
Future next = scheduler.schedule(this, replicationIntervalSeconds, TimeUnit.SECONDS);
scheduledPeriodicRef.set(next);
}
}- 在定时renew时，如果renew接口返回404（代表这个实例在EurekaServer上面找不到），可能是之前注册失败或者注册过期导致的。这时需要调用register重新注册
boolean renew() {
EurekaHttpResponse httpResponse;
try {
httpResponse = eurekaTransport.registrationClient.sendHeartBeat(instanceInfo.getAppName(), instanceInfo.getId(), instanceInfo, null);
logger.debug("{} - Heartbeat status: {}", PREFIX + appPathIdentifier, httpResponse.getStatusCode());
//如果renew接口返回404（代表这个实例在EurekaServer上面找不到），可能是之前注册失败或者注册过期导致的
if (httpResponse.getStatusCode() == 404) {
REREGISTER_COUNTER.increment();
logger.info("{} - Re-registering apps/{}", PREFIX + appPathIdentifier, instanceInfo.getAppName());
long timestamp = instanceInfo.setIsDirtyWithTime();
boolean success = register();
if (success) {
instanceInfo.unsetIsDirty(timestamp);
}
return success;
}
return httpResponse.getStatusCode() == 200;
} catch (Throwable e) {
logger.error("{} - was unable to send heartbeat!", PREFIX + appPathIdentifier, e);
return false;
}
}向Eureka发送注册请求EurekaServer发生了什么？
主要有两个存储，一个是之前提到过的registry，还有一个最近变化队列，后面我们会知道，这个最近变化队列里面就是客户端获取增量实例信息的内容：
# 整体注册信息缓存
private final ConcurrentHashMap<String, Map<String, Lease>> registry = new ConcurrentHashMap<String, Map<String, Lease>>();
# 最近变化队列
private ConcurrentLinkedQueue recentlyChangedQueue = new ConcurrentLinkedQueue(); EurekaServer收到实例注册主要分两步：
- 调用父类方法注册
- 同步到其他EurekaServer实例
public void register(InstanceInfo info, boolean isReplication) {
int leaseDuration = 90;
if (info.getLeaseInfo() != null && info.getLeaseInfo().getDurationInSecs() > 0) {
leaseDuration = info.getLeaseInfo().getDurationInSecs();
}
//调用父类方法注册
super.register(info, leaseDuration, isReplication);
//同步到其他EurekaServer实例
this.replicateToPeers(PeerAwareInstanceRegistryImpl.Action.Register, info.getAppName(), info.getId(), info, (InstanceStatus)null, isReplication);
}我们先看同步到其他EurekaServer实例
其实就是，注册到的EurekaServer再依次调用其他集群内的EurekaServer的Register方法将实例信息同步过去
private void replicateToPeers(Action action, String appName, String id,
InstanceInfo info /* optional */,
InstanceStatus newStatus /* optional */, boolean isReplication) {
Stopwatch tracer = action.getTimer().start();
try {
if (isReplication) {
numberOfReplicationsLastMin.increment();
}
// If it is a replication already, do not replicate again as this will create a poison replication
if (peerEurekaNodes == Collections.EMPTY_LIST || isReplication) {
return;
}
for (final PeerEurekaNode node : peerEurekaNodes.getPeerEurekaNodes()) {
// If the url represents this host, do not replicate to yourself.
if (peerEurekaNodes.isThisMyUrl(node.getServiceUrl())) {
continue;
}
replicateInstanceActionsToPeers(action, appName, id, info, newStatus, node);
}
} finally {
tracer.stop();
}
}
private void replicateInstanceActionsToPeers(Action action, String appName,
String id, InstanceInfo info, InstanceStatus newStatus,
PeerEurekaNode node) {
try {
InstanceInfo infoFromRegistry = null;
CurrentRequestVersion.set(Version.V2);
switch (action) {
case Cancel:
node.cancel(appName, id);
break;
case Heartbeat:
InstanceStatus overriddenStatus = overriddenInstanceStatusMap.get(id);
infoFromRegistry = getInstanceByAppAndId(appName, id, false);
node.heartbeat(appName, id, infoFromRegistry, overriddenStatus, false);
break;
case Register:
node.register(info);
break;
case StatusUpdate:
infoFromRegistry = getInstanceByAppAndId(appName, id, false);
node.statusUpdate(appName, id, newStatus, infoFromRegistry);
break;
case DeleteStatusOverride:
infoFromRegistry = getInstanceByAppAndId(appName, id, false);
node.deleteStatusOverride(appName, id, infoFromRegistry);
break;
}
} catch (Throwable t) {
logger.error("Cannot replicate information to {} for action {}", node.getServiceUrl(), action.name(), t);
}
}然后看看调用父类方法注册：
public void register(InstanceInfo registrant, int leaseDuration, boolean isReplication) {
try {
//register虽然看上去好像是修改，但是这里用的是读锁，后面会解释
read.lock();
//从registry中查看这个app是否存在
Map> gMap = registry.get(registrant.getAppName());
//不存在就创建
if (gMap == null) {
final ConcurrentHashMap> gNewMap = new ConcurrentHashMap>();
gMap = registry.putIfAbsent(registrant.getAppName(), gNewMap);
if (gMap == null) {
gMap = gNewMap;
}
}
//查看这个app的这个实例是否已存在
Lease existingLease = gMap.get(registrant.getId());
if (existingLease != null && (existingLease.getHolder() != null)) {
//如果已存在，对比时间戳，保留比较新的实例信息......
} else {
// 如果不存在，证明是一个新的实例
//更新自我保护监控变量的值的代码.....
}
Lease lease = new Lease(registrant, leaseDuration);
if (existingLease != null) {
lease.setServiceUpTimestamp(existingLease.getServiceUpTimestamp());
}
//放入registry
gMap.put(registrant.getId(), lease);
//加入最近修改的记录队列
recentlyChangedQueue.add(new RecentlyChangedItem(lease));
//初始化状态，记录时间等相关代码......
//主动让Response缓存失效
invalidateCache(registrant.getAppName(), registrant.getVIPAddress(), registrant.getSecureVipAddress());
} finally {
read.unlock();
}
}总结起来，就是主要三件事：
1.将实例注册信息放入或者更新registry
2.将实例注册信息加入最近修改的记录队列
3.主动让Response缓存失效
我们来类比下服务取消
服务取消CANCEL
protected boolean internalCancel(String appName, String id, boolean isReplication) {
try {
//cancel虽然看上去好像是修改，但是这里用的是读锁，后面会解释
read.lock();
//从registry中剔除这个实例
Map> gMap = registry.get(appName);
Lease leaseToCancel = null;
if (gMap != null) {
leaseToCancel = gMap.remove(id);
}
if (leaseToCancel == null) {
logger.warn("DS: Registry: cancel failed because Lease is not registered for: {}/{}", appName, id);
return false;
} else {
//改变状态，记录状态修改时间等相关代码......
if (instanceInfo != null) {
instanceInfo.setActionType(ActionType.DELETED);
//加入最近修改的记录队列
recentlyChangedQueue.add(new RecentlyChangedItem(leaseToCancel));
}
//主动让Response缓存失效
invalidateCache(appName, vip, svip);
logger.info("Cancelled instance {}/{} (replication={})", appName, id, isReplication);
return true;
}
} finally {
read.unlock();
}
}总结起来，也是主要三件事：
1.从registry中剔除这个实例
2.将实例注册信息加入最近修改的记录队列
3.主动让Response缓存失效
这里我们注意到了这个最近修改队列，我们来详细看看
最近修改队列
这个最近修改队列和消费者定时获取服务实例列表有着密切的关系
private TimerTask getDeltaRetentionTask() {
return new TimerTask() {
@Override
public void run() {
Iterator it = recentlyChangedQueue.iterator();
while (it.hasNext()) {
if (it.next().getLastUpdateTime() <
System.currentTimeMillis() - serverConfig.getRetentionTimeInMSInDeltaQueue()) {
it.remove();
} else {
break;
}
}
}
};
}这个RetentionTimeInMSInDeltaQueue默认是180s（配置是eureka.server.retention-time-in-m-s-in-delta-queue,默认是180s，官网写错了），可以看出这个队列是一个长度为180s的滑动窗口，保存最近180s以内的应用实例信息修改，后面我们会看到，客户端调用获取增量信息，实际上就是从这个queue中读取，所以可能一段时间内读取到的信息都是一样的。
Response缓存
Response缓存的实现类是ResponseCacheImpl，主要包括如下缓存field：
private final ConcurrentMap readOnlyCacheMap = new ConcurrentHashMap();
private final LoadingCache readWriteCacheMap;一个是guava的loadingcache，一个是普通的ConcurrentHashMap
这个loadingcache的初始化：
this.readWriteCacheMap = CacheBuilder.newBuilder().initialCapacity(1000)
.expireAfterWrite(serverConfig.getResponseCacheAutoExpirationInSeconds(), TimeUnit.SECONDS)
.removalListener(new RemovalListener() {
@Override
public void onRemoval(RemovalNotification notification) {
Key removedKey = notification.getKey();
if (removedKey.hasRegions()) {
Key cloneWithNoRegions = removedKey.cloneWithoutRegions();
regionSpecificKeys.remove(cloneWithNoRegions, removedKey);
}
}
})
.build(new CacheLoader() {
@Override
public Value load(Key key) throws Exception {
if (key.hasRegions()) {
Key cloneWithNoRegions = key.cloneWithoutRegions();
regionSpecificKeys.put(cloneWithNoRegions, key);
}
Value value = generatePayload(key);
return value;
}
});对于每个不存在的Key，会首先初始化，主要是调用generatePayload这个方法：
private Value generatePayload(Key key) {
Stopwatch tracer = null;
try {
String payload;
switch (key.getEntityType()) {
case Application:
boolean isRemoteRegionRequested = key.hasRegions();
if (ALL_APPS.equals(key.getName())) {
//获取所有应用信息
if (isRemoteRegionRequested) {
tracer = serializeAllAppsWithRemoteRegionTimer.start();
payload = getPayLoad(key, registry.getApplicationsFromMultipleRegions(key.getRegions()));
} else {
tracer = serializeAllAppsTimer.start();
payload = getPayLoad(key, registry.getApplications());
}
} else if (ALL_APPS_DELTA.equals(key.getName())) {
//获取所有应用增量信息
if (isRemoteRegionRequested) {
tracer = serializeDeltaAppsWithRemoteRegionTimer.start();
versionDeltaWithRegions.incrementAndGet();
versionDeltaWithRegionsLegacy.incrementAndGet();
payload = getPayLoad(key,
registry.getApplicationDeltasFromMultipleRegions(key.getRegions()));
} else {
tracer = serializeDeltaAppsTimer.start();
versionDelta.incrementAndGet();
versionDeltaLegacy.incrementAndGet();
payload = getPayLoad(key, registry.getApplicationDeltas());
}
} else {
//获取单个应用信息
tracer = serializeOneApptimer.start();
payload = getPayLoad(key, registry.getApplication(key.getName()));
}
break;
//其他类型我们不关心，先忽略掉相关代码
}
return new Value(payload);
} finally {
if (tracer != null) {
tracer.stop();
}
}
}获取所有应用信息，是从registry中直接拿registry.getApplications()，核心方法是getApplicationsFromMultipleRegions，看下简化过的源码：
public Applications getApplicationsFromMultipleRegions(String[] remoteRegions) {
boolean includeRemoteRegion = null != remoteRegions && remoteRegions.length != 0;
Applications apps = new Applications();
apps.setVersion(1L);
//将registry中的信息封装好放入Applications
for (Entry<String, Map<String, Lease>> entry : registry.entrySet()) {
Application app = null;
if (entry.getValue() != null) {
for (Entry<String, Lease> stringLeaseEntry : entry.getValue().entrySet()) {
Lease lease = stringLeaseEntry.getValue();
if (app == null) {
app = new Application(lease.getHolder().getAppName());
}
app.addInstance(decorateInstanceInfo(lease));
}
}
if (app != null) {
apps.addApplication(app);
}
}
//读取其他Region的Apps信息，我们目前不关心，略过这部分代码......
//设置AppsHashCode，在之后的介绍中，我们会提到，客户端读取到之后会对比这个AppsHashCode
apps.setAppsHashCode(apps.getReconcileHashCode());
return apps;
}获取所有应用增量信息，registry.getApplicationDeltas()：
public Applications getApplicationDeltas() {
Applications apps = new Applications();
apps.setVersion(responseCache.getVersionDelta().get());
Map applicationInstancesMap = new HashMap();
try {
//这里读取用的是写锁，下面我们就会解释为何这么用
write.lock();
//遍历recentlyChangedQueue，获取所有增量信息
Iterator iter = this.recentlyChangedQueue.iterator();
logger.debug("The number of elements in the delta queue is :"
+ this.recentlyChangedQueue.size());
while (iter.hasNext()) {
Lease lease = iter.next().getLeaseInfo();
InstanceInfo instanceInfo = lease.getHolder();
Object[] args = {instanceInfo.getId(),
instanceInfo.getStatus().name(),
instanceInfo.getActionType().name()};
logger.debug(
"The instance id %s is found with status %s and actiontype %s",
args);
Application app = applicationInstancesMap.get(instanceInfo
.getAppName());
if (app == null) {
app = new Application(instanceInfo.getAppName());
applicationInstancesMap.put(instanceInfo.getAppName(), app);
apps.addApplication(app);
}
app.addInstance(decorateInstanceInfo(lease));
}
//读取其他Region的Apps信息，我们目前不关心，略过这部分代码......
Applications allApps = getApplications(!disableTransparentFallback);
//设置AppsHashCode，在之后的介绍中，我们会提到，客户端读取到之后更新好自己的Apps缓存之后会对比这个AppsHashCode，如果不一样，就会进行一次全量Apps信息请求
apps.setAppsHashCode(allApps.getReconcileHashCode());
return apps;
} finally {
write.unlock();
}
}为何这里读写锁这么用，首先我们来分析下这个锁保护的对象是谁，可以很明显的看出，是recentlyChangedQueue这个队列。那么谁在修改这个队列，谁又在读取呢？ 每个服务实例注册，取消的时候，都会修改这个队列，这个队列是多线程修改的。但是读取，只有loadingcache的ALL_APPS_DELTAkey初始化线程会读取，而且在缓存失效前都不会再有线程读取。所以可以归纳为，多线程频繁修改，但是单线程不频繁读取。 如果没有锁，那么recentlyChangedQueue在遍历读取时如果遇到修改，就会抛出并发修改异常。如果用writeLock锁住多线程修改，那么同一时间只有一个线程能修改，效率不好。所以。利用读锁锁住多线程修改，利用写锁锁住单线程读取正好符合这里的场景。
前面提到，EurekaClient的查询请求，都是从ResponseCache中获取（从ResponseCache本身缓存的就是请求）。ResponseCache还包括readOnlyCacheMap，这个默认时启用的，就是用户请求会先从readOnlyCacheMap读取，如果readOnlyCacheMap中不存在，则从上面介绍的readWriteCacheMap中获取，之后再放入readOnlyCacheMap。
Value getValue(final Key key, boolean useReadOnlyCache) {
Value payload = null;
try {
if (useReadOnlyCache) {
final Value currentPayload = readOnlyCacheMap.get(key);
if (currentPayload != null) {
payload = currentPayload;
} else {
payload = readWriteCacheMap.get(key);
readOnlyCacheMap.put(key, payload);
}
} else {
payload = readWriteCacheMap.get(key);
}
} catch (Throwable t) {
logger.error("Cannot get value for key :" + key, t);
}
return payload;
}还有个定时任务：每隔只读缓存刷新时间将ReadWriteMap的信息复制到ReadOnlyMap上面：这个readOnlyCacheMap里面数据是定时从readWriteCacheMap中拷贝出来的：
private TimerTask getCacheUpdateTask() {
return new TimerTask() {
@Override
public void run() {
logger.debug("Updating the client cache from response cache");
for (Key key : readOnlyCacheMap.keySet()) {
if (logger.isDebugEnabled()) {
Object[] args = {key.getEntityType(), key.getName(), key.getVersion(), key.getType()};
logger.debug("Updating the client cache from response cache for key : {} {} {} {}", args);
}
try {
CurrentRequestVersion.set(key.getVersion());
Value cacheValue = readWriteCacheMap.get(key);
Value currentCacheValue = readOnlyCacheMap.get(key);
if (cacheValue != currentCacheValue) {
readOnlyCacheMap.put(key, cacheValue);
}
} catch (Throwable th) {
logger.error("Error while updating the client cache from response cache", th);
}
}
}
};
}在本篇最开始的时候提到register和cancel都会主动失效对应的ResponseCache，这个主动失效的源代码是：
public void invalidate(String appName, @Nullable String vipAddress, @Nullable String secureVipAddress) {
for (Key.KeyType type : Key.KeyType.values()) {
for (Version v : Version.values()) {
//对于任意一个APP缓存失效，都要让对应的APP请求响应，全量APP信息请求响应，增量APP信息请求响应失效
invalidate(
new Key(Key.EntityType.Application, appName, type, v, EurekaAccept.full),
new Key(Key.EntityType.Application, appName, type, v, EurekaAccept.compact),
new Key(Key.EntityType.Application, ALL_APPS, type, v, EurekaAccept.full),
new Key(Key.EntityType.Application, ALL_APPS, type, v, EurekaAccept.compact),
new Key(Key.EntityType.Application, ALL_APPS_DELTA, type, v, EurekaAccept.full),
new Key(Key.EntityType.Application, ALL_APPS_DELTA, type, v, EurekaAccept.compact)
);
if (null != vipAddress) {
invalidate(new Key(Key.EntityType.VIP, vipAddress, type, v, EurekaAccept.full));
}
if (null != secureVipAddress) {
invalidate(new Key(Key.EntityType.SVIP, secureVipAddress, type, v, EurekaAccept.full));
}
}
}
}
public void invalidate(Key... keys) {
for (Key key : keys) {
logger.debug("Invalidating the response cache key : {} {} {} {}, {}",
key.getEntityType(), key.getName(), key.getVersion(), key.getType(), key.getEurekaAccept());
readWriteCacheMap.invalidate(key);
Collection<Key> keysWithRegions = regionSpecificKeys.get(key);
if (null != keysWithRegions && !keysWithRegions.isEmpty()) {
for (Key keysWithRegion : keysWithRegions) {
logger.debug("Invalidating the response cache key : {} {} {} {} {}",
key.getEntityType(), key.getName(), key.getVersion(), key.getType(), key.getEurekaAccept());
readWriteCacheMap.invalidate(keysWithRegion);
}
}
}
}在readWriteCacheMap中使对应的APP请求响应，全量APP信息请求响应，增量APP信息请求响应失效后，下次请求，就会再读取registry生成。对于registry，新加入的应用或者实例会被读取到。对于cancel，退出的应用或者实例也会被去除掉
所以，总结起来，用下面这张图展示下EurekaServer 重要缓存和对应的请求：
image
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原始发表：2017-11-29 ，如有侵权请联系 cloudcommunity@tencent.com 删除
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