eureka client增量抓取机制
每隔30S抓取注册表
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private void initScheduledTasks() {
//初始化抓取注册表定时任务
if (clientConfig.shouldFetchRegistry()) {
// registry cache refresh timer
//抓取注册表间隔-秒
int registryFetchIntervalSeconds = clientConfig.getRegistryFetchIntervalSeconds();
//重试最大次数
int expBackOffBound = clientConfig.getCacheRefreshExecutorExponentialBackOffBound();
//创建并执行延时任务-每隔30S抓取注册表
scheduler.schedule(
new TimedSupervisorTask(
"cacheRefresh",
scheduler,
cacheRefreshExecutor,
registryFetchIntervalSeconds,
TimeUnit.SECONDS,
expBackOffBound,
new CacheRefreshThread()
),
registryFetchIntervalSeconds, TimeUnit.SECONDS);
}
...
增量抓取策略
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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 (...)
{
...
//全量抓取策略
getAndStoreFullRegistry();
} else {
//增量抓取策略
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();
}
}
// Notify about cache refresh before updating the instance remote status
onCacheRefreshed();
// Update remote status based on refreshed data held in the cache
updateInstanceRemoteStatus();
// registry was fetched successfully, so return true
return true;
}
调用restful接口
使用EurekaHttpClient.getDelta()，GET请求http://localhost:8080/v2/apps/delta。
eureka server端查询增量数据
ApplicationsResource中getContainerDifferential()方法为获取增量数据。使用ALL_APPS_DELTA从readOnlyCacheMap中获取数据，而ALL_APPS_DELTA的数据放入readWriteCacheMap时做区分。
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Key cacheKey = new Key(Key.EntityType.Application,
ResponseCacheImpl.ALL_APPS_DELTA,
keyType, CurrentRequestVersion.get(), EurekaAccept.fromString(eurekaAccept), regions
);
readWriteCacheMap加载数据
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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())) {
...
} else if (ALL_APPS_DELTA.equals(key.getName())) {
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 {
tracer = serializeOneApptimer.start();
payload = getPayLoad(key, registry.getApplication(key.getName()));
}
break;
...
}
return new Value(payload);
} finally {
if (tracer != null) {
tracer.stop();
}
}
}
recentlyChangedQueue增量更新机制
recentlyChangedQueue中存放新注册、下线等服务实例。在Registry构造时定义一个Timer定时任务，每隔30S查看服务实例变更记录，是否在队列中停留超过180S，如果超过就删除。这个queue只保留3分钟的服务实例变更记录。
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private ConcurrentLinkedQueue<RecentlyChangedItem> recentlyChangedQueue = new ConcurrentLinkedQueue<RecentlyChangedItem>();
//定时器执行每隔30S
this.deltaRetentionTimer.schedule(getDeltaRetentionTask(),
serverConfig.getDeltaRetentionTimerIntervalInMs(),
serverConfig.getDeltaRetentionTimerIntervalInMs());
//剔除超过3分钟的服务实例信息
private TimerTask getDeltaRetentionTask() {
return new TimerTask() {
@Override
public void run() {
Iterator<RecentlyChangedItem> it = recentlyChangedQueue.iterator();
while (it.hasNext()) {
if (it.next().getLastUpdateTime() <
System.currentTimeMillis() - serverConfig.getRetentionTimeInMSInDeltaQueue()) {
it.remove();
} else {
break;
}
}
}
};
}
增量更新合并至本地注册表
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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) {
...
getAndStoreFullRegistry();
} else if (fetchRegistryGeneration.compareAndSet(currentUpdateGeneration, currentUpdateGeneration + 1)) {
logger.debug("Got delta update with apps hashcode {}", delta.getAppsHashCode());
String reconcileHashCode = "";
if (fetchRegistryUpdateLock.tryLock()) {
try {
//增量更新合并至本地注册表
updateDelta(delta);
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
//对比hashcode
if (!reconcileHashCode.equals(delta.getAppsHashCode()) || clientConfig.shouldLogDeltaDiff()) {
reconcileAndLogDifference(delta, reconcileHashCode); // this makes a remoteCall
}
} else {
}
}
private void updateDelta(Applications delta) {
int deltaCount = 0;
for (Application app : delta.getRegisteredApplications()) {
for (InstanceInfo instance : app.getInstances()) {
Applications applications = getApplications();
String instanceRegion = instanceRegionChecker.getInstanceRegion(instance);
if (!instanceRegionChecker.isLocalRegion(instanceRegion)) {
Applications remoteApps = remoteRegionVsApps.get(instanceRegion);
if (null == remoteApps) {
remoteApps = new Applications();
remoteRegionVsApps.put(instanceRegion, remoteApps);
}
applications = remoteApps;
}
++deltaCount;
if (ActionType.ADDED.equals(instance.getActionType())) {
Application existingApp = applications.getRegisteredApplications(instance.getAppName());
if (existingApp == null) {
applications.addApplication(app);
}
logger.debug("Added instance {} to the existing apps in region {}", instance.getId(), instanceRegion);
applications.getRegisteredApplications(instance.getAppName()).addInstance(instance);
} else if (ActionType.MODIFIED.equals(instance.getActionType())) {
Application existingApp = applications.getRegisteredApplications(instance.getAppName());
if (existingApp == null) {
applications.addApplication(app);
}
logger.debug("Modified instance {} to the existing apps ", instance.getId());
applications.getRegisteredApplications(instance.getAppName()).addInstance(instance);
} else if (ActionType.DELETED.equals(instance.getActionType())) {
Application existingApp = applications.getRegisteredApplications(instance.getAppName());
if (existingApp == null) {
applications.addApplication(app);
}
logger.debug("Deleted instance {} to the existing apps ", instance.getId());
applications.getRegisteredApplications(instance.getAppName()).removeInstance(instance);
}
}
}
logger.debug("The total number of instances fetched by the delta processor : {}", deltaCount);
getApplications().setVersion(delta.getVersion());
getApplications().shuffleInstances(clientConfig.shouldFilterOnlyUpInstances());
for (Applications applications : remoteRegionVsApps.values()) {
applications.setVersion(delta.getVersion());
applications.shuffleInstances(clientConfig.shouldFilterOnlyUpInstances());
}
}
对比hashcode
增量更新合并至本地注册表后，计算hashcode与eureka server端返回的delta里的appsHashCode进行对比，如果不一样会重新从eureka server拉取全量注册表更新到本地缓存。
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// There is a diff in number of instances for some reason
if (!reconcileHashCode.equals(delta.getAppsHashCode()) || clientConfig.shouldLogDeltaDiff()) {
reconcileAndLogDifference(delta, reconcileHashCode); // this makes a remoteCall
}
//全量抓取注册表并记录对比异常信息
private void reconcileAndLogDifference(Applications delta, String reconcileHashCode) throws Throwable {
EurekaHttpResponse<Applications> httpResponse = clientConfig.getRegistryRefreshSingleVipAddress() == null
? eurekaTransport.queryClient.getApplications(remoteRegionsRef.get())
: eurekaTransport.queryClient.getVip(clientConfig.getRegistryRefreshSingleVipAddress(), remoteRegionsRef.get());
Applications serverApps = httpResponse.getEntity();
...
if (fetchRegistryGeneration.compareAndSet(currentUpdateGeneration, currentUpdateGeneration + 1)) {
localRegionApps.set(this.filterAndShuffle(serverApps));
getApplications().setVersion(delta.getVersion());
...
} else {
...
}
}
亮点
增量数据
如果保存一份增量的最新变更数据，可以基于LinkedQuueue，将最新变更的数据放入这个queue中，然后后台使用定时任务，每隔一定时间，将在队列中存放超过一定时间的数据移除，保持队列中就是最近几分钟内的变更的增量数据。
数据同步的hash值比对机制
在分布式系统里，进行数据的同步，可以采用Hash值的思想：从一个地方的数据计算一个hash值，到另外一个地方，计算一个hash值，保证两个hash值是一样的，确保这个数据传输过程中，没有出什么问题。
