Eureka-Client
注册表抓取都是在初始化DiscoveryClient的时候触发，initScheduledTasks()方法会开始定时任务不间断的抓取。
DiscoveryClient(ApplicationInfoManager applicationInfoManager, EurekaClientConfig config, AbstractDiscoveryClientOptionalArgs args,
Provider<BackupRegistry> backupRegistryProvider) {
// 省略......
// 抓取注册表
if (clientConfig.shouldFetchRegistry() && !fetchRegistry(false)) {
fetchRegistryFromBackup();
}
// call and execute the pre registration handler before all background tasks (inc registration) is started
if (this.preRegistrationHandler != null) {
this.preRegistrationHandler.beforeRegistration();
}
// 初始化调度任务
initScheduledTasks();
// 省略......
}
进入initScheduledTasks()方法
private void initScheduledTasks() {
if (clientConfig.shouldFetchRegistry()) {
// registry cache refresh timer
int registryFetchIntervalSeconds = clientConfig.getRegistryFetchIntervalSeconds();
int expBackOffBound = clientConfig.getCacheRefreshExecutorExponentialBackOffBound();
// 拉取注册表（全量/增量）
scheduler.schedule(
new TimedSupervisorTask(
"cacheRefresh",
scheduler,
cacheRefreshExecutor,
registryFetchIntervalSeconds,
TimeUnit.SECONDS,
expBackOffBound,
new CacheRefreshThread()
),
registryFetchIntervalSeconds, TimeUnit.SECONDS);
}
// 省略......
}
执行抓取注册表的逻辑是在CacheRefreshThread的run方法，然后调用refreshRegistry()方法，默认30s
class CacheRefreshThread implements Runnable {
public void run() {
refreshRegistry();
}
}
@VisibleForTesting
void refreshRegistry() {
try {
// 省略......
boolean success = fetchRegistry(remoteRegionsModified);
if (success) {
registrySize = localRegionApps.get().size();
lastSuccessfulRegistryFetchTimestamp = System.currentTimeMillis();
}
// 省略......
} catch (Throwable e) {
logger.error("Cannot fetch registry from server", e);
}
}
进入refreshRegistry()方法
private boolean fetchRegistry(boolean forceFullRegistryFetch) {
Stopwatch tracer = FETCH_REGISTRY_TIMER.start();
try {
// If the delta is disabled or if it is the first time, get all
// applications
Applications applications = getApplications();
if (clientConfig.shouldDisableDelta()
|| (!Strings.isNullOrEmpty(clientConfig.getRegistryRefreshSingleVipAddress()))
|| forceFullRegistryFetch
|| (applications == null)
|| (applications.getRegisteredApplications().size() == 0)
|| (applications.getVersion() == -1)) //Client application does not have latest library supporting delta
{
logger.info("Disable delta property : {}", clientConfig.shouldDisableDelta());
logger.info("Single vip registry refresh property : {}", clientConfig.getRegistryRefreshSingleVipAddress());
logger.info("Force full registry fetch : {}", forceFullRegistryFetch);
logger.info("Application is null : {}", (applications == null));
logger.info("Registered Applications size is zero : {}",
(applications.getRegisteredApplications().size() == 0));
logger.info("Application version is -1: {}", (applications.getVersion() == -1));
// 全量抓取
getAndStoreFullRegistry();
} else {
// 增量抓取
getAndUpdateDelta(applications);
}
applications.setAppsHashCode(applications.getReconcileHashCode());
logTotalInstances();
} catch (Throwable e) {
logger.error(PREFIX + appPathIdentifier + " - was unable to refresh its cache! status = " + e.getMessage(), e);
return false;
} finally {
if (tracer != null) {
tracer.stop();
}
}
return true;
}
进入getAndStoreFullRegistry()方法
private void getAndStoreFullRegistry() throws Throwable {
long currentUpdateGeneration = fetchRegistryGeneration.get();
logger.info("Getting all instance registry info from the eureka server");
Applications apps = null;
EurekaHttpResponse<Applications> httpResponse = clientConfig.getRegistryRefreshSingleVipAddress() == null
? eurekaTransport.queryClient.getApplications(remoteRegionsRef.get())
: eurekaTransport.queryClient.getVip(clientConfig.getRegistryRefreshSingleVipAddress(), remoteRegionsRef.get());
if (httpResponse.getStatusCode() == Status.OK.getStatusCode()) {
apps = httpResponse.getEntity();
}
logger.info("The response status is {}", httpResponse.getStatusCode());
if (apps == null) {
logger.error("The application is null for some reason. Not storing this information");
} else if (fetchRegistryGeneration.compareAndSet(currentUpdateGeneration, currentUpdateGeneration + 1)) {
localRegionApps.set(this.filterAndShuffle(apps));
logger.debug("Got full registry with apps hashcode {}", apps.getAppsHashCode());
} else {
logger.warn("Not updating applications as another thread is updating it already");
}
}
最后把拉取到的全量Applications放到localRegionApps中。
进入getAndUpdateDelta(Applications applications)方法
private void getAndUpdateDelta(Applications applications) throws Throwable {
long currentUpdateGeneration = fetchRegistryGeneration.get();
Applications delta = null;
EurekaHttpResponse<Applications> httpResponse = eurekaTransport.queryClient.getDelta(remoteRegionsRef.get());
if (httpResponse.getStatusCode() == Status.OK.getStatusCode()) {
delta = httpResponse.getEntity();
}
if (delta == null) {
logger.warn("The server does not allow the delta revision to be applied because it is not safe. "
+ "Hence got the full registry.");
getAndStoreFullRegistry();
} else if (fetchRegistryGeneration.compareAndSet(currentUpdateGeneration, currentUpdateGeneration + 1)) {
logger.debug("Got delta update with apps hashcode {}", delta.getAppsHashCode());
String reconcileHashCode = "";
if (fetchRegistryUpdateLock.tryLock()) {
try {
// 增量更新
updateDelta(delta);
// 计算所有本地服务的hashcode
reconcileHashCode = getReconcileHashCode(applications);
} finally {
fetchRegistryUpdateLock.unlock();
}
} else {
logger.warn("Cannot acquire update lock, aborting getAndUpdateDelta");
}
// There is a diff in number of instances for some reason
if (!reconcileHashCode.equals(delta.getAppsHashCode()) || clientConfig.shouldLogDeltaDiff()) {
// 如果本地服务的hashcode与增量服务的hashcode不同会全量拉取
reconcileAndLogDifference(delta, reconcileHashCode); // this makes a remoteCall
}
} else {
logger.warn("Not updating application delta as another thread is updating it already");
logger.debug("Ignoring delta update with apps hashcode {}, as another thread is updating it already", delta.getAppsHashCode());
}
}
增量服务的hashcode不只是增量服务，而是所拉取的增量服务那台eureka-server所有的本地服务的hashcode，会在eureka-server源码剖析中看到。
进入getReconcileHashCode(Applications applications)方法
private String getReconcileHashCode(Applications applications) {
TreeMap<String, AtomicInteger> instanceCountMap = new TreeMap<String, AtomicInteger>();
if (isFetchingRemoteRegionRegistries()) {
for (Applications remoteApp : remoteRegionVsApps.values()) {
remoteApp.populateInstanceCountMap(instanceCountMap);
}
}
applications.populateInstanceCountMap(instanceCountMap);
return Applications.getReconcileHashCode(instanceCountMap);
}
再进入populateInstanceCountMap(TreeMap<String, AtomicInteger> instanceCountMap)方法中
public void populateInstanceCountMap(TreeMap<String, AtomicInteger> instanceCountMap) {
for (Application app : this.getRegisteredApplications()) {
for (InstanceInfo info : app.getInstancesAsIsFromEureka()) {
AtomicInteger instanceCount = instanceCountMap.get(info.getStatus().name());
if (instanceCount == null) {
instanceCount = new AtomicInteger(0);
instanceCountMap.put(info.getStatus().name(), instanceCount);
}
instanceCount.incrementAndGet();
}
}
}
此处会把info.getStatus().name()作为instanceCountMap的key,在这里曾有个小疑问，为什么不加上服务名称service-name,如果此时一个服务的实例下线，另一个服务的实例上线，服务注册表已经变化，但是Hashcode已经变化，这样不一致，其实这个担心是多余的，所有变化的服务都会变成增量，所以没必要加service-name。
Eureka-Server
全量抓取注册表的代码
增量抓取注册表的代码
增量/全量注册表是从responseCache缓存中获取的，进入responseCache.get(cacheKey)方法
public String get(final Key key) {
return get(key, shouldUseReadOnlyResponseCache);
}
@VisibleForTesting
String get(final Key key, boolean useReadOnlyCache) {
Value payload = getValue(key, useReadOnlyCache);
if (payload == null || payload.getPayload().equals(EMPTY_PAYLOAD)) {
return null;
} else {
return payload.getPayload();
}
}
再进入getValue(key, useReadOnlyCache)方法
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;
}
从该方法中我们可以看到有两个缓存map,readOnlyCacheMap和readWriteCacheMap，可以知道eureka用了两级缓存，这两个map是在ResponseCacheImpl构造方法中初始化的
进入ResponseCacheImpl构造方法
ResponseCacheImpl(EurekaServerConfig serverConfig, ServerCodecs serverCodecs, AbstractInstanceRegistry registry) {
this.serverConfig = serverConfig;
this.serverCodecs = serverCodecs;
this.shouldUseReadOnlyResponseCache = serverConfig.shouldUseReadOnlyResponseCache();
this.registry = registry;
long responseCacheUpdateIntervalMs = serverConfig.getResponseCacheUpdateIntervalMs();
this.readWriteCacheMap =
CacheBuilder.newBuilder().initialCapacity(1000)
.expireAfterWrite(serverConfig.getResponseCacheAutoExpirationInSeconds(), TimeUnit.SECONDS)
.removalListener(new RemovalListener<Key, Value>() {
@Override
public void onRemoval(RemovalNotification<Key, Value> notification) {
Key removedKey = notification.getKey();
if (removedKey.hasRegions()) {
Key cloneWithNoRegions = removedKey.cloneWithoutRegions();
regionSpecificKeys.remove(cloneWithNoRegions, removedKey);
}
}
})
.build(new CacheLoader<Key, Value>() {
@Override
public Value load(Key key) throws Exception {
if (key.hasRegions()) {
Key cloneWithNoRegions = key.cloneWithoutRegions();
regionSpecificKeys.put(cloneWithNoRegions, key);
}
// 抓取注册表（全量/增量）
Value value = generatePayload(key);
return value;
}
});
// 定时更新readOnlyCacheMap
if (shouldUseReadOnlyResponseCache) {
timer.schedule(getCacheUpdateTask(),
new Date(((System.currentTimeMillis() / responseCacheUpdateIntervalMs) * responseCacheUpdateIntervalMs)
+ responseCacheUpdateIntervalMs),
responseCacheUpdateIntervalMs);
}
try {
Monitors.registerObject(this);
} catch (Throwable e) {
logger.warn("Cannot register the JMX monitor for the InstanceRegistry", e);
}
}
此处用了谷歌的LoadingCache，在这里不做分析，
进入generatePayload(key)方法
private Value generatePayload(Key key) {
Stopwatch tracer = null;
try {
String payload;
switch (key.getEntityType()) {
case Application:
boolean isRemoteRegionRequested = key.hasRegions();
// 全量
if (ALL_APPS.equals(key.getName())) {
if (isRemoteRegionRequested) {
tracer = serializeAllAppsWithRemoteRegionTimer.start();
payload = getPayLoad(key, registry.getApplicationsFromMultipleRegions(key.getRegions()));
} else {
tracer = serializeAllAppsTimer.start();
// 全量
payload = getPayLoad(key, registry.getApplications());
}
} else if (ALL_APPS_DELTA.equals(key.getName())) {
// 增量
if (isRemoteRegionRequested) {
tracer = serializeDeltaAppsWithRemoteRegionTimer.start();
versionDeltaWithRegions.incrementAndGet();
versionDeltaWithRegionsLegacy.incrementAndGet();
// 增量
payload = getPayLoad(key,
registry.getApplicationDeltasFromMultipleRegions(key.getRegions()));
} else {
tracer = serializeDeltaAppsTimer.start();
versionDelta.incrementAndGet();
versionDeltaLegacy.incrementAndGet();
payload = getPayLoad(key, registry.getApplicationDeltas());
}
} else {
tracer = serializeOneApptimer.start();
payload = getPayLoad(key, registry.getApplication(key.getName()));
}
break;
// 省略......
}
}
在这个方法里可以看到registry.getApplications()和registry.getApplicationDeltasFromMultipleRegions(key.getRegions())两个方法，一个全量，一个增量，我们只分析增量方法。
进入registry.getApplicationDeltas()方法
public Applications getApplicationDeltas() {
GET_ALL_CACHE_MISS_DELTA.increment();
Applications apps = new Applications();
apps.setVersion(responseCache.getVersionDelta().get());
Map<String, Application> applicationInstancesMap = new HashMap<String, Application>();
try {
write.lock();
Iterator<RecentlyChangedItem> iter = this.recentlyChangedQueue.iterator();
logger.debug("The number of elements in the delta queue is :"
+ this.recentlyChangedQueue.size());
while (iter.hasNext()) {
Lease<InstanceInfo> 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));
}
boolean disableTransparentFallback = serverConfig.disableTransparentFallbackToOtherRegion();
if (!disableTransparentFallback) {
Applications allAppsInLocalRegion = getApplications(false);
for (RemoteRegionRegistry remoteRegistry : this.regionNameVSRemoteRegistry.values()) {
Applications applications = remoteRegistry.getApplicationDeltas();
for (Application application : applications.getRegisteredApplications()) {
Application appInLocalRegistry =
allAppsInLocalRegion.getRegisteredApplications(application.getName());
if (appInLocalRegistry == null) {
apps.addApplication(application);
}
}
}
}
Applications allApps = getApplications(!disableTransparentFallback);
// 此处就是把所有服务的Hashcode赋给增量服务,用户client端的hashcode比对
apps.setAppsHashCode(allApps.getReconcileHashCode());
return apps;
} finally {
write.unlock();
}
}
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来源：https://blog.csdn.net/manongxx/category_10951792.html