序

本文主要研究一下eureka的delta配置

client端配置

    {"sourceType": "org.springframework.cloud.netflix.eureka.EurekaClientConfigBean","defaultValue": false,"name": "eureka.client.disable-delta","description": "Indicates whether the eureka client should disable fetching of delta and should\n rather resort to getting the full registry information.\n\n Note that the delta fetches can reduce the traffic tremendously, because the rate\n of change with the eureka server is normally much lower than the rate of fetches.\n\n The changes are effective at runtime at the next registry fetch cycle as specified\n by registryFetchIntervalSeconds","type": "java.lang.Boolean"},{"sourceType": "org.springframework.cloud.netflix.eureka.EurekaClientConfigBean","defaultValue": false,"name": "eureka.client.log-delta-diff","description": "Indicates whether to log differences between the eureka server and the eureka\n client in terms of registry information.\n\n Eureka client tries to retrieve only delta changes from eureka server to minimize\n network traffic. After receiving the deltas, eureka client reconciles the\n information from the server to verify it has not missed out some information.\n Reconciliation failures could happen when the client has had network issues\n communicating to server.If the reconciliation fails, eureka client gets the full\n registry information.\n\n While getting the full registry information, the eureka client can log the\n differences between the client and the server and this setting controls that.\n\n The changes are effective at runtime at the next registry fetch cycle as specified\n by registryFetchIntervalSecondsr","type": "java.lang.Boolean"}

DiscoveryClient.fetchRegistry

eureka-client-1.8.8-sources.jar!/com/netflix/discovery/DiscoveryClient.java

    /*** Fetches the registry information.** <p>* This method tries to get only deltas after the first fetch unless there* is an issue in reconciling eureka server and client registry information.* </p>** @param forceFullRegistryFetch Forces a full registry fetch.** @return true if the registry was fetched*/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// applicationsApplications 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));getAndStoreFullRegistry();} else {getAndUpdateDelta(applications);}applications.setAppsHashCode(applications.getReconcileHashCode());logTotalInstances();} catch (Throwable e) {logger.error(PREFIX + "{} - was unable to refresh its cache! status = {}", appPathIdentifier, e.getMessage(), e);return false;} finally {if (tracer != null) {tracer.stop();}}// Notify about cache refresh before updating the instance remote statusonCacheRefreshed();// Update remote status based on refreshed data held in the cacheupdateInstanceRemoteStatus();// registry was fetched successfully, so return truereturn true;}

如果禁用了delta，则client端则调用getAndStoreFullRegistry()全量接口；开启的话，则调用getAndUpdateDelta(applications)，对本地region的applications进行delta更新。

getAndUpdateDelta

    /*** Get the delta registry information from the eureka server and update it locally.* When applying the delta, the following flow is observed:** if (update generation have not advanced (due to another thread))*   atomically try to: update application with the delta and get reconcileHashCode*   abort entire processing otherwise*   do reconciliation if reconcileHashCode clash* fi** @return the client response* @throws Throwable on error*/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 {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 reasonif (!reconcileHashCode.equals(delta.getAppsHashCode()) || clientConfig.shouldLogDeltaDiff()) {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());}}

这里可以看到，如果开启了logDeltaDiff的话，则会调用reconcileAndLogDifference方法 另外这里底层请求的是queryClient.getDelta(remoteRegionsRef.get())方法

DiscoveryClient.updateDelta

eureka-client-1.8.8-sources.jar!/com/netflix/discovery/DiscoveryClient.java

    /*** Updates the delta information fetches from the eureka server into the* local cache.** @param delta*            the delta information received from eureka server in the last*            poll cycle.*/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());}}

可以看到这里根据获取的delta数据的ActionType来修改本地的数据

queryClient.getDelta

eureka-client-1.8.8-sources.jar!/com/netflix/discovery/shared/transport/jersey/AbstractJerseyEurekaHttpClient.java

    @Overridepublic EurekaHttpResponse<Applications> getDelta(String... regions) {return getApplicationsInternal("apps/delta", regions);}

可以看到请求的是/apps/delta接口

server端配置

    {"sourceType": "org.springframework.cloud.netflix.eureka.server.EurekaServerConfigBean","defaultValue": false,"name": "eureka.server.disable-delta","type": "java.lang.Boolean"},{"sourceType": "org.springframework.cloud.netflix.eureka.server.EurekaServerConfigBean","defaultValue": 0,"name": "eureka.server.delta-retention-timer-interval-in-ms","type": "java.lang.Long"},{"sourceType": "org.springframework.cloud.netflix.eureka.server.EurekaServerConfigBean","defaultValue": 0,"name": "eureka.server.retention-time-in-m-s-in-delta-queue","type": "java.lang.Long"}

ApplicationsResource.getContainerDifferential

eureka-core-1.8.8-sources.jar!/com/netflix/eureka/resources/ApplicationsResource.java

    /*** Get information about all delta changes in {@link com.netflix.discovery.shared.Applications}.** <p>* The delta changes represent the registry information change for a period* as configured by* {@link EurekaServerConfig#getRetentionTimeInMSInDeltaQueue()}. The* changes that can happen in a registry include* <em>Registrations,Cancels,Status Changes and Expirations</em>. Normally* the changes to the registry are infrequent and hence getting just the* delta will be much more efficient than getting the complete registry.* </p>** <p>* Since the delta information is cached over a period of time, the requests* may return the same data multiple times within the window configured by* {@link EurekaServerConfig#getRetentionTimeInMSInDeltaQueue()}.The clients* are expected to handle this duplicate information.* <p>** @param version the version of the request.* @param acceptHeader the accept header to indicate whether to serve  JSON or XML data.* @param acceptEncoding the accept header to indicate whether to serve compressed or uncompressed data.* @param eurekaAccept an eureka accept extension, see {@link com.netflix.appinfo.EurekaAccept}* @param uriInfo  the {@link java.net.URI} information of the request made.* @return response containing the delta information of the*         {@link AbstractInstanceRegistry}.*/@Path("delta")@GETpublic Response getContainerDifferential(@PathParam("version") String version,@HeaderParam(HEADER_ACCEPT) String acceptHeader,@HeaderParam(HEADER_ACCEPT_ENCODING) String acceptEncoding,@HeaderParam(EurekaAccept.HTTP_X_EUREKA_ACCEPT) String eurekaAccept,@Context UriInfo uriInfo, @Nullable @QueryParam("regions") String regionsStr) {boolean isRemoteRegionRequested = null != regionsStr && !regionsStr.isEmpty();// If the delta flag is disabled in discovery or if the lease expiration// has been disabled, redirect clients to get all instancesif ((serverConfig.shouldDisableDelta()) || (!registry.shouldAllowAccess(isRemoteRegionRequested))) {return Response.status(Status.FORBIDDEN).build();}String[] regions = null;if (!isRemoteRegionRequested) {EurekaMonitors.GET_ALL_DELTA.increment();} else {regions = regionsStr.toLowerCase().split(",");Arrays.sort(regions); // So we don't have different caches for same regions queried in different order.EurekaMonitors.GET_ALL_DELTA_WITH_REMOTE_REGIONS.increment();}CurrentRequestVersion.set(Version.toEnum(version));KeyType keyType = Key.KeyType.JSON;String returnMediaType = MediaType.APPLICATION_JSON;if (acceptHeader == null || !acceptHeader.contains(HEADER_JSON_VALUE)) {keyType = Key.KeyType.XML;returnMediaType = MediaType.APPLICATION_XML;}Key cacheKey = new Key(Key.EntityType.Application,ResponseCacheImpl.ALL_APPS_DELTA,keyType, CurrentRequestVersion.get(), EurekaAccept.fromString(eurekaAccept), regions);if (acceptEncoding != null&& acceptEncoding.contains(HEADER_GZIP_VALUE)) {return Response.ok(responseCache.getGZIP(cacheKey)).header(HEADER_CONTENT_ENCODING, HEADER_GZIP_VALUE).header(HEADER_CONTENT_TYPE, returnMediaType).build();} else {return Response.ok(responseCache.get(cacheKey)).build();}}

server端提供/apps/delta接口

ResponseCacheImpl.generatePayload

eureka-core-1.8.8-sources.jar!/com/netflix/eureka/registry/ResponseCacheImpl.java

    /** Generate pay load for the given key.*/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())) {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())) {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;case VIP:case SVIP:tracer = serializeViptimer.start();payload = getPayLoad(key, getApplicationsForVip(key, registry));break;default:logger.error("Unidentified entity type: {} found in the cache key.", key.getEntityType());payload = "";break;}return new Value(payload);} finally {if (tracer != null) {tracer.stop();}}}

这里提供了缓存不存在时触发的方法，具体重点看ALL_APPS_DELTA的方法，重点调用了registry.getApplicationDeltas()及registry.getApplicationDeltasFromMultipleRegions方法

registry.getApplicationDeltas()

    /*** Get the registry information about the delta changes. The deltas are* cached for a window specified by* {@link EurekaServerConfig#getRetentionTimeInMSInDeltaQueue()}. Subsequent* requests for delta information may return the same information and client* must make sure this does not adversely affect them.** @return all application deltas.* @deprecated use {@link #getApplicationDeltasFromMultipleRegions(String[])} instead. This method has a* flawed behavior of transparently falling back to a remote region if no instances for an app is available locally.* The new behavior is to explicitly specify if you need a remote region.*/@Deprecatedpublic 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();logger.debug("The instance id {} is found with status {} and actiontype {}",instanceInfo.getId(), instanceInfo.getStatus().name(), instanceInfo.getActionType().name());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);apps.setAppsHashCode(allApps.getReconcileHashCode());return apps;} finally {write.unlock();}}

可以看到这里主要是从recentlyChangedQueue取数据

recentlyChangedQueue

    private ConcurrentLinkedQueue<RecentlyChangedItem> recentlyChangedQueue = new ConcurrentLinkedQueue<RecentlyChangedItem>();

这里存放的是RecentlyChangedItem AbstractInstanceRegistry在register、cancel、statusUpdate、deleteStatus等操作里头都会往该队列添加RecentlyChangedItem

deltaRetentionTimer

eureka-core-1.8.8-sources.jar!/com/netflix/eureka/registry/AbstractInstanceRegistry.java

    protected AbstractInstanceRegistry(EurekaServerConfig serverConfig, EurekaClientConfig clientConfig, ServerCodecs serverCodecs) {this.serverConfig = serverConfig;this.clientConfig = clientConfig;this.serverCodecs = serverCodecs;this.recentCanceledQueue = new CircularQueue<Pair<Long, String>>(1000);this.recentRegisteredQueue = new CircularQueue<Pair<Long, String>>(1000);this.renewsLastMin = new MeasuredRate(1000 * 60 * 1);this.deltaRetentionTimer.schedule(getDeltaRetentionTask(),serverConfig.getDeltaRetentionTimerIntervalInMs(),serverConfig.getDeltaRetentionTimerIntervalInMs());}

这里初始化了DeltaRetentionTask，调度间隔是serverConfig.getDeltaRetentionTimerIntervalInMs()，默认是30 * 1000

DeltaRetentionTask

eureka-core-1.8.8-sources.jar!/com/netflix/eureka/registry/ResponseCacheImpl.java

    private TimerTask getDeltaRetentionTask() {return new TimerTask() {@Overridepublic void run() {Iterator<RecentlyChangedItem> it = recentlyChangedQueue.iterator();while (it.hasNext()) {if (it.next().getLastUpdateTime() <System.currentTimeMillis() - serverConfig.getRetentionTimeInMSInDeltaQueue()) {it.remove();} else {break;}}}};}

该任务主要是距离上次更新时间超过serverConfig.getRetentionTimeInMSInDeltaQueue()的值给remove掉 serverConfig.getRetentionTimeInMSInDeltaQueue()的值默认为3 * MINUTES

小结

eureka提供了delta参数，在client端及server端都有。client端主要是控制刷新registry的时候，是否使用调用/apps/delta接口，然后根据返回数据的ActionType来作用于本地数据。而server端则提供/apps/delta接口，它的主要逻辑是在registry的修改操作都会放recentlyChangedQueue存放RecentlyChangedItem事件，然后有个定时任务去剔除距离上次更新时间超过指定阈值的item；而查询接口则是从recentlyChangedQueue获取数据然后返回。

client端主要是eureka.client.disable-delta、eureka.client.log-delta-diff两个参数；server端主要是eureka.server.disable-delta、eureka.server.delta-retention-timer-interval-in-ms、eureka.server.retention-time-in-m-s-in-delta-queue三个参数。

doc

• Eureka REST operations