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注册中心 Eureka 源码解析 —— 应用实例注册发现(六)之全量获取

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本文主要基于 Eureka 1.8.X 版本


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1. 概述

本文主要分享 Eureka-Client 向 Eureka-Server 获取全量注册信息的过程

FROM 《深度剖析服务发现组件Netflix Eureka》

Eureka-Client 获取注册信息,分成全量获取增量获取。默认配置下,Eureka-Client 启动时,首先执行一次全量获取进行本地缓存注册信息,而后每 30增量获取刷新本地缓存( 非“正常”情况下会是全量获取 )。

本文重点在于全量获取

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2. Eureka-Client 发起全量获取

本小节调用关系如下:

2.1 初始化全量获取

Eureka-Client 启动时,首先执行一次全量获取进行本地缓存注册信息,首先代码如下:

// DiscoveryClient.java
/**
* Applications 在本地的缓存
*/
private final AtomicReference<Applications> localRegionApps = new AtomicReference<Applications>();

DiscoveryClient(ApplicationInfoManager applicationInfoManager, EurekaClientConfig config, AbstractDiscoveryClientOptionalArgs args,
                    Provider<BackupRegistry> backupRegistryProvider) {
                    
     // ... 省略无关代码
     
    // 【3.2.5】初始化应用集合在本地的缓存
    localRegionApps.set(new Applications());
     
    // ... 省略无关代码     
     
    // 【3.2.12】从 Eureka-Server 拉取注册信息
    if (clientConfig.shouldFetchRegistry() && !fetchRegistry(false)) {
        fetchRegistryFromBackup();
    }
     
     // ... 省略无关代码       
}
复制代码
  • com.netflix.discovery.shared.Applications,注册的应用集合。较为容易理解,点击 链接 链接查看带中文注释的类,这里就不啰嗦了。Applications 与 InstanceInfo 类关系如下:

  • 配置 eureka.shouldFetchRegistry = true,开启从 Eureka-Server 获取注册信息。默认值:true

  • 调用 #fetchRegistry(false) 方法,从 Eureka-Server 全量获取注册信息,在 「2.4 发起获取注册信息」 详细解析。

2.2 定时获取

Eureka-Client 在初始化过程中,创建获取注册信息线程,固定间隔向 Eureka-Server 发起获取注册信息( fetch ),刷新本地注册信息缓存。实现代码如下:

// DiscoveryClient.java
DiscoveryClient(ApplicationInfoManager applicationInfoManager, EurekaClientConfig config, AbstractDiscoveryClientOptionalArgs args,
               Provider<BackupRegistry> backupRegistryProvider) {
    // ... 省略无关代码
               
    // 【3.2.9】初始化线程池
    // default size of 2 - 1 each for heartbeat and cacheRefresh
    scheduler = Executors.newScheduledThreadPool(2,
         new ThreadFactoryBuilder()
                 .setNameFormat("DiscoveryClient-%d")
                 .setDaemon(true)
                 .build());
    
    cacheRefreshExecutor = new ThreadPoolExecutor(
         1, clientConfig.getCacheRefreshExecutorThreadPoolSize(), 0, TimeUnit.SECONDS,
         new SynchronousQueue<Runnable>(),
         new ThreadFactoryBuilder()
                 .setNameFormat("DiscoveryClient-CacheRefreshExecutor-%d")
                 .setDaemon(true)
                 .build()
     );  // use direct handoff
    
    // ... 省略无关代码
    
    // 【3.2.14】初始化定时任务
    initScheduledTasks();
    
    // ... 省略无关代码
}

private void initScheduledTasks() {
    // 向 Eureka-Server 心跳(续租)执行器
    if (clientConfig.shouldFetchRegistry()) {
       // registry cache refresh timer
       int registryFetchIntervalSeconds = clientConfig.getRegistryFetchIntervalSeconds();
       int expBackOffBound = clientConfig.getCacheRefreshExecutorExponentialBackOffBound();
       scheduler.schedule(
               new TimedSupervisorTask(
                       "cacheRefresh",
                       scheduler,
                       cacheRefreshExecutor,
                       registryFetchIntervalSeconds,
                       TimeUnit.SECONDS,
                       expBackOffBound,
                       new CacheRefreshThread()
               ),
               registryFetchIntervalSeconds, TimeUnit.SECONDS);
     }
     // ... 省略无关代码
}
复制代码

2.3 刷新注册信息缓存

调用 #refreshRegistry(false) 方法,刷新注册信息缓存,实现代码如下:

// DiscoveryClient.java
  1: void refreshRegistry() {
  2:     try {
  3:         // TODO 芋艿:TODO[0009]:RemoteRegionRegistry
  4:         boolean isFetchingRemoteRegionRegistries = isFetchingRemoteRegionRegistries();
  5: 
  6:         boolean remoteRegionsModified = false;
  7:         // This makes sure that a dynamic change to remote regions to fetch is honored.
  8:         String latestRemoteRegions = clientConfig.fetchRegistryForRemoteRegions();
  9:         if (null != latestRemoteRegions) {
 10:             String currentRemoteRegions = remoteRegionsToFetch.get();
 11:             if (!latestRemoteRegions.equals(currentRemoteRegions)) {
 12:                 // Both remoteRegionsToFetch and AzToRegionMapper.regionsToFetch need to be in sync
 13:                 synchronized (instanceRegionChecker.getAzToRegionMapper()) {
 14:                     if (remoteRegionsToFetch.compareAndSet(currentRemoteRegions, latestRemoteRegions)) {
 15:                         String[] remoteRegions = latestRemoteRegions.split(",");
 16:                         remoteRegionsRef.set(remoteRegions);
 17:                         instanceRegionChecker.getAzToRegionMapper().setRegionsToFetch(remoteRegions);
 18:                         remoteRegionsModified = true;
 19:                     } else {
 20:                         logger.info("Remote regions to fetch modified concurrently," +
 21:                                 " ignoring change from {} to {}", currentRemoteRegions, latestRemoteRegions);
 22:                     }
 23:                 }
 24:             } else {
 25:                 // Just refresh mapping to reflect any DNS/Property change
 26:                 instanceRegionChecker.getAzToRegionMapper().refreshMapping();
 27:             }
 28:         }
 29: 
 30:         boolean success = fetchRegistry(remoteRegionsModified);
 31:         if (success) {
 32:             // 设置 注册信息的应用实例数
 33:             registrySize = localRegionApps.get().size();
 34:             // 设置 最后获取注册信息时间
 35:             lastSuccessfulRegistryFetchTimestamp = System.currentTimeMillis();
 36:         }
 37: 
 38:         // 打印日志
 39:         if (logger.isDebugEnabled()) {
 40:             StringBuilder allAppsHashCodes = new StringBuilder();
 41:             allAppsHashCodes.append("Local region apps hashcode: ");
 42:             allAppsHashCodes.append(localRegionApps.get().getAppsHashCode());
 43:             allAppsHashCodes.append(", is fetching remote regions? ");
 44:             allAppsHashCodes.append(isFetchingRemoteRegionRegistries);
 45:             for (Map.Entry<String, Applications> entry : remoteRegionVsApps.entrySet()) {
 46:                 allAppsHashCodes.append(", Remote region: ");
 47:                 allAppsHashCodes.append(entry.getKey());
 48:                 allAppsHashCodes.append(" , apps hashcode: ");
 49:                 allAppsHashCodes.append(entry.getValue().getAppsHashCode());
 50:             }
 51:             logger.debug("Completed cache refresh task for discovery. All Apps hash code is {} ",
 52:                     allAppsHashCodes.toString());
 53:         }
 54:     } catch (Throwable e) {
 55:         logger.error("Cannot fetch registry from server", e);
 56:     }        
 57: }
复制代码
  • 第 3 至 28 行 :TODO[0009]:RemoteRegionRegistry

  • 第 30 行 :调用 #fetchRegistry(false) 方法,从 Eureka-Server 获取注册信息,在 「2.4 发起获取注册信息」 详细解析。

  • 第 31 至 36 行 :获取注册信息成功,设置注册信息的应用实例数,最后获取注册信息时间。变量代码如下:

    /**
    * 注册信息的应用实例数
    */
    private volatile int registrySize = 0;
    /**
    * 最后成功从 Eureka-Server 拉取注册信息时间戳
    */
    private volatile long lastSuccessfulRegistryFetchTimestamp = -1;
    复制代码
  • 第 38 至 53 行 :打印调试日志。

  • 第 54 至 56 行 :打印异常日志。

2.4 发起获取注册信息

调用 #fetchRegistry(false) 方法,从 Eureka-Server 获取注册信息( 根据条件判断,可能是全量,也可能是增量 ),实现代码如下:

  1: private boolean fetchRegistry(boolean forceFullRegistryFetch) {
  2:     Stopwatch tracer = FETCH_REGISTRY_TIMER.start();
  3: 
  4:     try {
  5:         // 获取 本地缓存的注册的应用实例集合
  6:         // If the delta is disabled or if it is the first time, get all
  7:         // applications
  8:         Applications applications = getApplications();
  9: 
 10:         // 全量获取
 11:         if (clientConfig.shouldDisableDelta() // 禁用增量获取
 12:                 || (!Strings.isNullOrEmpty(clientConfig.getRegistryRefreshSingleVipAddress()))
 13:                 || forceFullRegistryFetch
 14:                 || (applications == null) // 空
 15:                 || (applications.getRegisteredApplications().size() == 0) // 空
 16:                 || (applications.getVersion() == -1)) //Client application does not have latest library supporting delta
 17:         {
 18:             logger.info("Disable delta property : {}", clientConfig.shouldDisableDelta());
 19:             logger.info("Single vip registry refresh property : {}", clientConfig.getRegistryRefreshSingleVipAddress());
 20:             logger.info("Force full registry fetch : {}", forceFullRegistryFetch);
 21:             logger.info("Application is null : {}", (applications == null));
 22:             logger.info("Registered Applications size is zero : {}",
 23:                     (applications.getRegisteredApplications().size() == 0));
 24:             logger.info("Application version is -1: {}", (applications.getVersion() == -1));
 25:             // 执行 全量获取
 26:             getAndStoreFullRegistry();
 27:         } else {
 28:             // 执行 增量获取
 29:             getAndUpdateDelta(applications);
 30:         }
 31:         // 设置 应用集合 hashcode
 32:         applications.setAppsHashCode(applications.getReconcileHashCode());
 33:         // 打印 本地缓存的注册的应用实例数量
 34:         logTotalInstances();
 35:     } catch (Throwable e) {
 36:         logger.error(PREFIX + appPathIdentifier + " - was unable to refresh its cache! status = " + e.getMessage(), e);
 37:         return false;
 38:     } finally {
 39:         if (tracer != null) {
 40:             tracer.stop();
 41:         }
 42:     }
 43: 
 44:     // Notify about cache refresh before updating the instance remote status
 45:     onCacheRefreshed();
 46: 
 47:     // Update remote status based on refreshed data held in the cache
 48:     updateInstanceRemoteStatus();
 49: 
 50:     // registry was fetched successfully, so return true
 51:     return true;
 52: }
复制代码
  • 第 5 至 8 行 :获取本地缓存的注册的应用实例集合,实现代码如下:

    public Applications getApplications() {
       return localRegionApps.get();
    }
    复制代码
  • 第 10 至 26 行 :全量获取注册信息。

    • 第 11 行 :配置 eureka.disableDelta = true ,禁用增量获取注册信息。默认值:false
    • 第 12 行 :只获得一个 vipAddress 对应的应用实例们的注册信息。
    • 第 13 行 :方法参数 forceFullRegistryFetch 强制全量获取注册信息。
    • 第 14 至 15 行 :本地缓存为空。
    • 第 25 至 26 行 :调用 #getAndStoreFullRegistry() 方法,全量获取注册信息,并设置到本地缓存。下文详细解析。
  • 第 27 至 30 行 :增量获取注册信息,并刷新本地缓存,在 《Eureka 源码解析 —— 应用实例注册发现 (七)之增量获取》 详细解析。

  • 第 31 至 32 行 :计算应用集合 hashcode 。该变量用于校验增量获取的注册信息和 Eureka-Server 全量的注册信息是否一致( 完整 ),在 《Eureka 源码解析 —— 应用实例注册发现 (七)之增量获取》 详细解析。

  • 第 33 至 34 行 :打印调试日志,输出本地缓存的注册的应用实例数量。实现代码如下:

    private void logTotalInstances() {
       if (logger.isDebugEnabled()) {
           int totInstances = 0;
           for (Application application : getApplications().getRegisteredApplications()) {
               totInstances += application.getInstancesAsIsFromEureka().size();
           }
           logger.debug("The total number of all instances in the client now is {}", totInstances);
       }
    }
    复制代码
  • 第 44 至 45 行 :触发 CacheRefreshedEvent 事件,事件监听器执行。目前 Eureka 未提供默认的该事件监听器。

    • #onCacheRefreshed() 方法,实现代码如下:

      /**
       * Eureka 事件监听器
       */
      private final CopyOnWriteArraySet<EurekaEventListener> eventListeners = new CopyOnWriteArraySet<>();
      
      protected void onCacheRefreshed() {
          fireEvent(new CacheRefreshedEvent());
      }
      
      protected void fireEvent(final EurekaEvent event) {
          for (EurekaEventListener listener : eventListeners) {
              listener.onEvent(event);
          }
      }
      复制代码
      • x
    • 笔者的YY :你可以实现自定义的事件监听器监听 CacheRefreshedEvent 事件,以达到持久化最新的注册信息到存储器( 例如,本地文件 ),通过这样的方式,配合实现 BackupRegistry 接口读取存储器。BackupRegistry 接口调用如下:

      // 【3.2.12】从 Eureka-Server 拉取注册信息
      if (clientConfig.shouldFetchRegistry() && !fetchRegistry(false)) {
          fetchRegistryFromBackup();
      }
      复制代码
  • 第47 至 48 行 :更新本地缓存的当前应用实例在 Eureka-Server 的状态。

      1: private volatile InstanceInfo.InstanceStatus lastRemoteInstanceStatus = InstanceInfo.InstanceStatus.UNKNOWN; 
      2: 
      3: private synchronized void updateInstanceRemoteStatus() {
      4:     // Determine this instance's status for this app and set to UNKNOWN if not found
      5:     InstanceInfo.InstanceStatus currentRemoteInstanceStatus = null;
      6:     if (instanceInfo.getAppName() != null) {
      7:         Application app = getApplication(instanceInfo.getAppName());
      8:         if (app != null) {
      9:             InstanceInfo remoteInstanceInfo = app.getByInstanceId(instanceInfo.getId());
     10:             if (remoteInstanceInfo != null) {
     11:                 currentRemoteInstanceStatus = remoteInstanceInfo.getStatus();
     12:             }
     13:         }
     14:     }
     15:     if (currentRemoteInstanceStatus == null) {
     16:         currentRemoteInstanceStatus = InstanceInfo.InstanceStatus.UNKNOWN;
     17:     }
     18: 
     19:     // Notify if status changed
     20:     if (lastRemoteInstanceStatus != currentRemoteInstanceStatus) {
     21:         onRemoteStatusChanged(lastRemoteInstanceStatus, currentRemoteInstanceStatus);
     22:         lastRemoteInstanceStatus = currentRemoteInstanceStatus;
     23:     }
     24: }
    复制代码
    • 第 4 至 14 行 :从注册信息中获取当前应用在 Eureka-Server 的状态。

    • 第 19 至 23 行 :对比本地缓存最新的的当前应用实例在 Eureka-Server 的状态,若不同,更新本地缓存( 注意,只更新该缓存变量,不更新本地当前应用实例的状态( instanceInfo.status ) ),触发 StatusChangeEvent 事件,事件监听器执行。目前 Eureka 未提供默认的该事件监听器。#onRemoteStatusChanged(...) 实现代码如下:

      protected void onRemoteStatusChanged(InstanceInfo.InstanceStatus oldStatus, InstanceInfo.InstanceStatus newStatus) {
         fireEvent(new StatusChangeEvent(oldStatus, newStatus));
      }
      复制代码

2.4.1 全量获取注册信息,并设置到本地缓存

调用 #getAndStoreFullRegistry() 方法,全量获取注册信息,并设置到本地缓存。下实现代码如下:

  1: private void getAndStoreFullRegistry() throws Throwable {
  2:     long currentUpdateGeneration = fetchRegistryGeneration.get();
  3: 
  4:     logger.info("Getting all instance registry info from the eureka server");
  5: 
  6:     // 全量获取注册信息
  7:     Applications apps = null;
  8:     EurekaHttpResponse<Applications> httpResponse = clientConfig.getRegistryRefreshSingleVipAddress() == null
  9:             ? eurekaTransport.queryClient.getApplications(remoteRegionsRef.get())
 10:             : eurekaTransport.queryClient.getVip(clientConfig.getRegistryRefreshSingleVipAddress(), remoteRegionsRef.get());
 11:     if (httpResponse.getStatusCode() == Status.OK.getStatusCode()) {
 12:         apps = httpResponse.getEntity();
 13:     }
 14:     logger.info("The response status is {}", httpResponse.getStatusCode());
 15: 
 16:     // 设置到本地缓存
 17:     if (apps == null) {
 18:         logger.error("The application is null for some reason. Not storing this information");
 19:     } else if (fetchRegistryGeneration.compareAndSet(currentUpdateGeneration, currentUpdateGeneration + 1)) {
 20:         localRegionApps.set(this.filterAndShuffle(apps));
 21:         logger.debug("Got full registry with apps hashcode {}", apps.getAppsHashCode());
 22:     } else {
 23:         logger.warn("Not updating applications as another thread is updating it already");
 24:     }
 25: }
复制代码
  • 第 6 至 14 行 :全量获取注册信息,实现代码如下:

    // AbstractJerseyEurekaHttpClient.java
    @Override
    public EurekaHttpResponse<Applications> getApplications(String... regions) {
       return getApplicationsInternal("apps/", regions);
    }
    
    private EurekaHttpResponse<Applications> getApplicationsInternal(String urlPath, String[] regions) {
       ClientResponse response = null;
       String regionsParamValue = null;
       try {
           WebResource webResource = jerseyClient.resource(serviceUrl).path(urlPath);
           if (regions != null && regions.length > 0) {
               regionsParamValue = StringUtil.join(regions);
               webResource = webResource.queryParam("regions", regionsParamValue);
           }
           Builder requestBuilder = webResource.getRequestBuilder();
           addExtraHeaders(requestBuilder);
           response = requestBuilder.accept(MediaType.APPLICATION_JSON_TYPE).get(ClientResponse.class); // JSON
    
           Applications applications = null;
           if (response.getStatus() == Status.OK.getStatusCode() && response.hasEntity()) {
               applications = response.getEntity(Applications.class);
           }
           return anEurekaHttpResponse(response.getStatus(), Applications.class)
                   .headers(headersOf(response))
                   .entity(applications)
                   .build();
       } finally {
           if (logger.isDebugEnabled()) {
               logger.debug("Jersey HTTP GET {}/{}?{}; statusCode={}",
                       serviceUrl, urlPath,
                       regionsParamValue == null ? "" : "regions=" + regionsParamValue,
                       response == null ? "N/A" : response.getStatus()
               );
           }
           if (response != null) {
               response.close();
           }
       }
    }
    复制代码
    • 调用 AbstractJerseyEurekaHttpClient#getApplications(...) 方法,GET 请求 Eureka-Server 的 apps/ 接口,参数为 regions ,返回格式为 JSON ,实现全量获取注册信息
  • 第 16 至 24 行 :设置到本地注册信息缓存

    • 第 19 行 :TODO[0025] :并发更新的情况???
    • 第 20 行 :调用 #filterAndShuffle(...) 方法,根据配置 eureka.shouldFilterOnlyUpInstances = true ( 默认值 :true ) 过滤只保留状态为开启( UP )的应用实例,并随机打乱应用实例顺序。打乱后,实现调用应用服务的随机性。代码比较易懂,点击链接查看方法实现。

3. Eureka-Server 接收全量获取

3.1 接收全量获取请求

com.netflix.eureka.resources.ApplicationsResource,处理所有应用的请求操作的 Resource ( Controller )。

接收全量获取请求,映射 ApplicationsResource#getContainers() 方法,实现代码如下:

  1: @GET
  2: public Response getContainers(@PathParam("version") String version,
  3:                               @HeaderParam(HEADER_ACCEPT) String acceptHeader,
  4:                               @HeaderParam(HEADER_ACCEPT_ENCODING) String acceptEncoding,
  5:                               @HeaderParam(EurekaAccept.HTTP_X_EUREKA_ACCEPT) String eurekaAccept,
  6:                               @Context UriInfo uriInfo,
  7:                               @Nullable @QueryParam("regions") String regionsStr) {
  8:     // TODO[0009]:RemoteRegionRegistry
  9:     boolean isRemoteRegionRequested = null != regionsStr && !regionsStr.isEmpty();
 10:     String[] regions = null;
 11:     if (!isRemoteRegionRequested) {
 12:         EurekaMonitors.GET_ALL.increment();
 13:     } else {
 14:         regions = regionsStr.toLowerCase().split(",");
 15:         Arrays.sort(regions); // So we don't have different caches for same regions queried in different order.
 16:         EurekaMonitors.GET_ALL_WITH_REMOTE_REGIONS.increment();
 17:     }
 18: 
 19:     // 判断是否可以访问
 20:     // Check if the server allows the access to the registry. The server can
 21:     // restrict access if it is not
 22:     // ready to serve traffic depending on various reasons.
 23:     if (!registry.shouldAllowAccess(isRemoteRegionRequested)) {
 24:         return Response.status(Status.FORBIDDEN).build();
 25:     }
 26: 
 27:     // API 版本
 28:     CurrentRequestVersion.set(Version.toEnum(version));
 29: 
 30:     // 返回数据格式
 31:     KeyType keyType = Key.KeyType.JSON;
 32:     String returnMediaType = MediaType.APPLICATION_JSON;
 33:     if (acceptHeader == null || !acceptHeader.contains(HEADER_JSON_VALUE)) {
 34:         keyType = Key.KeyType.XML;
 35:         returnMediaType = MediaType.APPLICATION_XML;
 36:     }
 37: 
 38:     // 响应缓存键( KEY )
 39:     Key cacheKey = new Key(Key.EntityType.Application,
 40:             ResponseCacheImpl.ALL_APPS,
 41:             keyType, CurrentRequestVersion.get(), EurekaAccept.fromString(eurekaAccept), regions
 42:     );
 43: 
 44:     //
 45:     Response response;
 46:     if (acceptEncoding != null && acceptEncoding.contains(HEADER_GZIP_VALUE)) {
 47:         response = Response.ok(responseCache.getGZIP(cacheKey))
 48:                 .header(HEADER_CONTENT_ENCODING, HEADER_GZIP_VALUE)
 49:                 .header(HEADER_CONTENT_TYPE, returnMediaType)
 50:                 .build();
 51:     } else {
 52:         response = Response.ok(responseCache.get(cacheKey))
 53:                 .build();
 54:     }
 55:     return response;
 56: }
复制代码
  • 第 8 至 17 行 :TODO[0009]:RemoteRegionRegistry

  • 第 19 至 25 行 :Eureka-Server 启动完成,但是未处于就绪( Ready )状态,不接受请求全量应用注册信息的请求,例如,Eureka-Server 启动时,未能从其他 Eureka-Server 集群的节点获取到应用注册信息。

  • 第 27 至 28 行 :设置 API 版本号。默认最新 API 版本为 V2。实现代码如下:

    public enum Version {
        V1, V2;
    
        public static Version toEnum(String v) {
            for (Version version : Version.values()) {
                if (version.name().equalsIgnoreCase(v)) {
                    return version;
                }
            }
            //Defaults to v2
            return V2;
        }
    }
    复制代码
  • 第 30 至 36 行 :设置返回数据格式,默认 JSON 。

  • 第 38 至 42 行 :创建响应缓存( ResponseCache ) 的键( KEY ),在 「3.2.1 缓存键」详细解析。

  • 第 44 至 55 行 :从响应缓存读取全量注册信息,在 「3.3 缓存读取」详细解析。

3.2 响应缓存 ResponseCache

com.netflix.eureka.registry.ResponseCache,响应缓存接口,接口代码如下:

public interface ResponseCache {

    String get(Key key);
    
    byte[] getGZIP(Key key);
    
    void invalidate(String appName, @Nullable String vipAddress, @Nullable String secureVipAddress);

    AtomicLong getVersionDelta();
    
    AtomicLong getVersionDeltaWithRegions();

}
复制代码
  • 其中,#getVersionDelta()#getVersionDeltaWithRegions() 已经废弃。这里保留的原因主要是考虑兼容性。判断依据来自如下代码:

    // Applications.java
    @Deprecated
    public void setVersion(Long version) {
       this.versionDelta = version;
    }
    
    // AbstractInstanceRegistry.java
    public Applications getApplicationDeltas() {
        // ... 省略其它无关代码
        apps.setVersion(responseCache.getVersionDelta().get()); // 唯一调用到 ResponseCache#getVersionDelta() 方法的地方
        // ... 省略其它无关代码
    }
    复制代码
  • #get() :获得缓存。

  • #getGZIP() :获得缓存,并 GZIP 。

  • #invalidate() :过期缓存。

3.2.1 缓存键

com.netflix.eureka.registry.Key,缓存键。实现代码如下:

public class Key {

    public enum KeyType {
        JSON, XML
    }

    /**
     * An enum to define the entity that is stored in this cache for this key.
     */
    public enum EntityType {
        Application, VIP, SVIP
    }

    /**
     * 实体名
     */
    private final String entityName;
    /**
     * TODO[0009]:RemoteRegionRegistry
     */
    private final String[] regions;
    /**
     * 请求参数类型
     */
    private final KeyType requestType;
    /**
     * 请求 API 版本号
     */
    private final Version requestVersion;
    /**
     * hashKey
     */
    private final String hashKey;
    /**
     * 实体类型
     *
     * {@link EntityType}
     */
    private final EntityType entityType;
    /**
     * {@link EurekaAccept}
     */
    private final EurekaAccept eurekaAccept;
    
    public Key(EntityType entityType, String entityName, KeyType type, Version v, EurekaAccept eurekaAccept, @Nullable String[] regions) {
        this.regions = regions;
        this.entityType = entityType;
        this.entityName = entityName;
        this.requestType = type;
        this.requestVersion = v;
        this.eurekaAccept = eurekaAccept;
        hashKey = this.entityType + this.entityName + (null != this.regions ? Arrays.toString(this.regions) : "")
                + requestType.name() + requestVersion.name() + this.eurekaAccept.name();
    }
    
    public Key(EntityType entityType, String entityName, KeyType type, Version v, EurekaAccept eurekaAccept, @Nullable String[] regions) {
        this.regions = regions;
        this.entityType = entityType;
        this.entityName = entityName;
        this.requestType = type;
        this.requestVersion = v;
        this.eurekaAccept = eurekaAccept;
        hashKey = this.entityType + this.entityName + (null != this.regions ? Arrays.toString(this.regions) : "")
                + requestType.name() + requestVersion.name() + this.eurekaAccept.name();
    }
    
    @Override
    public int hashCode() {
        String hashKey = getHashKey();
        return hashKey.hashCode();
    }

    @Override
    public boolean equals(Object other) {
        if (other instanceof Key) {
            return getHashKey().equals(((Key) other).getHashKey());
        } else {
            return false;
        }
    }
    
}
复制代码

3.2.2 响应缓存实现类

com.netflix.eureka.registry.ResponseCacheImpl,响应缓存实现类。

在 ResponseCacheImpl 里,将缓存拆分成两层 :

  • 只读缓存( readOnlyCacheMap )
  • 固定过期 + 固定大小读写缓存( readWriteCacheMap )

默认配置下,缓存读取策略如下:

缓存过期策略如下:

  • 应用实例注册、下线、过期时,只只只过期 readWriteCacheMap
  • readWriteCacheMap 写入一段时间( 可配置 )后自动过期。
  • 定时任务对比 readWriteCacheMapreadOnlyCacheMap 的缓存值,若不一致,以前者为主。通过这样的方式,实现了 readOnlyCacheMap 的定时过期。

注意:应用实例注册、下线、过期时,不会很快刷新到 readWriteCacheMap 缓存里。默认配置下,最大延迟在 30 秒。

为什么可以使用缓存?

CAP 的选择上,Eureka 选择了 AP ,不同于 Zookeeper 选择了 CP 。

推荐阅读:

3.3 缓存读取

调用 ResponseCacheImpl#get(...) 方法( #getGzip(...) 类似 ),读取缓存,实现代码如下:

  1: private final ConcurrentMap<Key, Value> readOnlyCacheMap = new ConcurrentHashMap<Key, Value>();
  2: 
  3: private final LoadingCache<Key, Value> readWriteCacheMap;
  4: 
  5: public String get(final Key key) {
  6:     return get(key, shouldUseReadOnlyResponseCache);
  7: }
  8: 
  9: String get(final Key key, boolean useReadOnlyCache) {
 10:     Value payload = getValue(key, useReadOnlyCache);
 11:     if (payload == null || payload.getPayload().equals(EMPTY_PAYLOAD)) {
 12:         return null;
 13:     } else {
 14:         return payload.getPayload();
 15:     }
 16: }
 17: 
 18: Value getValue(final Key key, boolean useReadOnlyCache) {
 19:     Value payload = null;
 20:     try {
 21:         if (useReadOnlyCache) {
 22:             final Value currentPayload = readOnlyCacheMap.get(key);
 23:             if (currentPayload != null) {
 24:                 payload = currentPayload;
 25:             } else {
 26:                 payload = readWriteCacheMap.get(key);
 27:                 readOnlyCacheMap.put(key, payload);
 28:             }
 29:         } else {
 30:             payload = readWriteCacheMap.get(key);
 31:         }
 32:     } catch (Throwable t) {
 33:         logger.error("Cannot get value for key :" + key, t);
 34:     }
 35:     return payload;
 36: }
复制代码
  • 第 5 至 7 行 :调用 #get(key, useReadOnlyCache) 方法,读取缓存。其中 shouldUseReadOnlyResponseCache 通过配置 eureka.shouldUseReadOnlyResponseCache = true (默认值 :true ) 开启只读缓存。如果你对数据的一致性有相对高的要求,可以关闭这个开关,当然因为少了 readOnlyCacheMap ,性能会有一定的下降。

  • 第 9 至 16 行 :调用 getValue(key, useReadOnlyCache) 方法,读取缓存。从 readOnlyCacheMapreadWriteCacheMap 变量可以看到缓存值的类为 com.netflix.eureka.registry.ResponseCacheImpl.Value ,实现代码如下:

    public class Value {
    
       /**
        * 原始值
        */
       private final String payload;
       /**
        * GZIP 压缩后的值
        */
       private byte[] gzipped;
    
       public Value(String payload) {
           this.payload = payload;
           if (!EMPTY_PAYLOAD.equals(payload)) {
               // ... 省略 GZIP 压缩代码
               gzipped = bos.toByteArray();
           } else {
               gzipped = null;
           }
       }
    
       public String getPayload() {
           return payload;
       }
    
       public byte[] getGzipped() {
           return gzipped;
       }
    
    }
    复制代码
  • 第 21 至 31 行 :读取缓存。

    • 第 21 至 28 行 :先读取 readOnlyCacheMap 。读取不到,读取 readWriteCacheMap ,并设置到 readOnlyCacheMap

    • 第 29 至 31 行 :读取 readWriteCacheMap

    • readWriteCacheMap 实现代码如下:

      this.readWriteCacheMap =
            CacheBuilder.newBuilder().initialCapacity(1000)
                    .expireAfterWrite(serverConfig.getResponseCacheAutoExpirationInSeconds(), TimeUnit.SECONDS)
                    .removalListener(new RemovalListener<Key, Value>() {
                        @Override
                        public void onRemoval(RemovalNotification<Key, Value> notification) {
                            // TODO[0009]:RemoteRegionRegistry
                            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 {
                            // // TODO[0009]:RemoteRegionRegistry
                            if (key.hasRegions()) {
                                Key cloneWithNoRegions = key.cloneWithoutRegions();
                                regionSpecificKeys.put(cloneWithNoRegions, key);
                            }
                            Value value = generatePayload(key);
                            return value;
                        }
                    });
      复制代码
      • readWriteCacheMap 最大缓存数量为 1000 。
      • 调用 #generatePayload(key) 方法,生成缓存值。
  • #generatePayload(key) 方法,实现代码如下:

      1: private Value generatePayload(Key key) {
      2:     Stopwatch tracer = null;
      3:     try {
      4:         String payload;
      5:         switch (key.getEntityType()) {
      6:             case Application:
      7:                 boolean isRemoteRegionRequested = key.hasRegions();
      8: 
      9:                 if (ALL_APPS.equals(key.getName())) {
     10:                     if (isRemoteRegionRequested) { // TODO[0009]:RemoteRegionRegistry
     11:                         tracer = serializeAllAppsWithRemoteRegionTimer.start();
     12:                         payload = getPayLoad(key, registry.getApplicationsFromMultipleRegions(key.getRegions()));
     13:                     } else {
     14:                         tracer = serializeAllAppsTimer.start();
     15:                         payload = getPayLoad(key, registry.getApplications());
     16:                     }
     17:                 } else if (ALL_APPS_DELTA.equals(key.getName())) {
     18:                     // ... 省略增量获取相关的代码
     19:                  } else {
     20:                     tracer = serializeOneApptimer.start();
     21:                     payload = getPayLoad(key, registry.getApplication(key.getName()));
     22:                 }
     23:                 break;
     24:             // ... 省略部分代码 
     25:         }
     26:         return new Value(payload);
     27:     } finally {
     28:         if (tracer != null) {
     29:             tracer.stop();
     30:         }
     31:     }
     32: }
    复制代码
    • 第 10 至 12 行 :TODO[0009]:RemoteRegionRegistry
    • 第 13 至 16 行 :调用 AbstractInstanceRegistry#getApplications() 方法,获得注册的应用集合。后调用 #getPayLoad() 方法,将注册的应用集合转换成缓存值。🙂 这两个方法代码较多,下面详细解析。
    • 第 17 至 18 行 :获取增量注册信息的缓存值,在 《Eureka 源码解析 —— 应用实例注册发现 (七)之增量获取》 详细解析。

3.3.1 获得注册的应用集合

调用 AbstractInstanceRegistry#getApplications() 方法,获得注册的应用集合,实现代码如下:

  1: // AbstractInstanceRegistry.java
  2: 
  3: private static final String[] EMPTY_STR_ARRAY = new String[0];
  4: 
  5: public Applications getApplications() {
  6:    boolean disableTransparentFallback = serverConfig.disableTransparentFallbackToOtherRegion();
  7:    if (disableTransparentFallback) { // TODO[0009]:RemoteRegionRegistry
  8:        return getApplicationsFromLocalRegionOnly();
  9:    } else {
 10:        return getApplicationsFromAllRemoteRegions();  // Behavior of falling back to remote region can be disabled.
 11:    }
 12: }
 13: 
 14: public Applications getApplicationsFromLocalRegionOnly() {
 15:    return getApplicationsFromMultipleRegions(EMPTY_STR_ARRAY);
 16: }
复制代码
  • 第 6 至 8 行 :TODO[0009]:RemoteRegionRegistry

  • 第 9 至 16 行 :调用 #getApplicationsFromMultipleRegions(...) 方法,获得注册的应用集合,实现代码如下:

      1: public Applications getApplicationsFromMultipleRegions(String[] remoteRegions) {
      2:     // TODO[0009]:RemoteRegionRegistry
      3:     boolean includeRemoteRegion = null != remoteRegions && remoteRegions.length != 0;
      4:     logger.debug("Fetching applications registry with remote regions: {}, Regions argument {}",
      5:             includeRemoteRegion, Arrays.toString(remoteRegions));
      6:     if (includeRemoteRegion) {
      7:         GET_ALL_WITH_REMOTE_REGIONS_CACHE_MISS.increment();
      8:     } else {
      9:         GET_ALL_CACHE_MISS.increment();
     10:     }
     11:     // 获得获得注册的应用集合
     12:     Applications apps = new Applications();
     13:     apps.setVersion(1L);
     14:     for (Entry<String, Map<String, Lease<InstanceInfo>>> entry : registry.entrySet()) {
     15:         Application app = null;
     16: 
     17:         if (entry.getValue() != null) {
     18:             for (Entry<String, Lease<InstanceInfo>> stringLeaseEntry : entry.getValue().entrySet()) {
     19:                 Lease<InstanceInfo> lease = stringLeaseEntry.getValue();
     20:                 if (app == null) {
     21:                     app = new Application(lease.getHolder().getAppName());
     22:                 }
     23:                 app.addInstance(decorateInstanceInfo(lease));
     24:             }
     25:         }
     26:         if (app != null) {
     27:             apps.addApplication(app);
     28:         }
     29:     }
     30:     // TODO[0009]:RemoteRegionRegistry
     31:     if (includeRemoteRegion) {
     32:         for (String remoteRegion : remoteRegions) {
     33:             RemoteRegionRegistry remoteRegistry = regionNameVSRemoteRegistry.get(remoteRegion);
     34:             if (null != remoteRegistry) {
     35:                 Applications remoteApps = remoteRegistry.getApplications();
     36:                 for (Application application : remoteApps.getRegisteredApplications()) {
     37:                     if (shouldFetchFromRemoteRegistry(application.getName(), remoteRegion)) {
     38:                         logger.info("Application {}  fetched from the remote region {}",
     39:                                 application.getName(), remoteRegion);
     40: 
     41:                         Application appInstanceTillNow = apps.getRegisteredApplications(application.getName());
     42:                         if (appInstanceTillNow == null) {
     43:                             appInstanceTillNow = new Application(application.getName());
     44:                             apps.addApplication(appInstanceTillNow);
     45:                         }
     46:                         for (InstanceInfo instanceInfo : application.getInstances()) {
     47:                             appInstanceTillNow.addInstance(instanceInfo);
     48:                         }
     49:                     } else {
     50:                         logger.debug("Application {} not fetched from the remote region {} as there exists a "
     51:                                         + "whitelist and this app is not in the whitelist.",
     52:                                 application.getName(), remoteRegion);
     53:                     }
     54:                 }
     55:             } else {
     56:                 logger.warn("No remote registry available for the remote region {}", remoteRegion);
     57:             }
     58:         }
     59:     }
     60:     // 设置 应用集合 hashcode
     61:     apps.setAppsHashCode(apps.getReconcileHashCode());
     62:     return apps;
     63: }
    复制代码
    • 第 2 至 第 10 行 :TODO[0009]:RemoteRegionRegistry
    • 第 11 至 29 行 :获得获得注册的应用集合。
    • 第 30 至 59 行 :TODO[0009]:RemoteRegionRegistry
    • 第 61 行 :计算应用集合 hashcode 。该变量用于校验增量获取的注册信息和 Eureka-Server 全量的注册信息是否一致( 完整 ),在 《Eureka 源码解析 —— 应用实例注册发现 (七)之增量获取》 详细解析。

3.3.2 转换成缓存值

调用 #getPayLoad() 方法,将注册的应用集合转换成缓存值,实现代码如下:

/**
* Generate pay load with both JSON and XML formats for all applications.
*/
private String getPayLoad(Key key, Applications apps) {
   // 获得编码器
   EncoderWrapper encoderWrapper = serverCodecs.getEncoder(key.getType(), key.getEurekaAccept());
   String result;
   try {
       // 编码
       result = encoderWrapper.encode(apps);
   } catch (Exception e) {
       logger.error("Failed to encode the payload for all apps", e);
       return "";
   }
   if(logger.isDebugEnabled()) {
       logger.debug("New application cache entry {} with apps hashcode {}", key.toStringCompact(), apps.getAppsHashCode());
   }
   return result;
}
复制代码

3.4 主动过期读写缓存

应用实例注册、下线、过期时,调用 ResponseCacheImpl#invalidate() 方法,主动过期读写缓存( readWriteCacheMap ),实现代码如下:

public void invalidate(String appName, @Nullable String vipAddress, @Nullable String secureVipAddress) {
   for (Key.KeyType type : Key.KeyType.values()) {
       for (Version v : Version.values()) {
           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));
           }
       }
   }
}
复制代码
  • 调用 #invalidate(keys) 方法,逐个过期每个缓存键值,实现代码如下:

    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());
           // 过期读写缓存
           readWriteCacheMap.invalidate(key);
           // TODO[0009]:RemoteRegionRegistry
           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);
               }
           }
       }
    }
    复制代码

3.5 被动过期读写缓存

读写缓存( readWriteCacheMap ) 写入后,一段时间自动过期,实现代码如下:

expireAfterWrite(serverConfig.getResponseCacheAutoExpirationInSeconds())
复制代码
  • 配置 eureka.responseCacheAutoExpirationInSeconds ,设置写入过期时长。默认值 :180 秒。

3.6 定时刷新只读缓存

定时任务对比 readWriteCacheMapreadOnlyCacheMap 的缓存值,若不一致,以前者为主。通过这样的方式,实现了 readOnlyCacheMap 的定时过期。实现代码如下:

  1: ResponseCacheImpl(EurekaServerConfig serverConfig, ServerCodecs serverCodecs, AbstractInstanceRegistry registry) {
  2:     // ... 省略无关代码 
  3: 
  4:     long responseCacheUpdateIntervalMs = serverConfig.getResponseCacheUpdateIntervalMs();
  5:     // ... 省略无关代码
  6: 
  7:     if (shouldUseReadOnlyResponseCache) {
  8:         timer.schedule(getCacheUpdateTask(),
  9:                 new Date(((System.currentTimeMillis() / responseCacheUpdateIntervalMs) * responseCacheUpdateIntervalMs)
 10:                         + responseCacheUpdateIntervalMs),
 11:                 responseCacheUpdateIntervalMs);
 12:     }
 13: 
 14:     // ... 省略无关代码
 15: }
 16: 
 17: private TimerTask getCacheUpdateTask() {
 18:     return new TimerTask() {
 19:         @Override
 20:         public void run() {
 21:             logger.debug("Updating the client cache from response cache");
 22:             for (Key key : readOnlyCacheMap.keySet()) { // 循环 readOnlyCacheMap 的缓存键
 23:                 if (logger.isDebugEnabled()) {
 24:                     Object[] args = {key.getEntityType(), key.getName(), key.getVersion(), key.getType()};
 25:                     logger.debug("Updating the client cache from response cache for key : {} {} {} {}", args);
 26:                 }
 27:                 try {
 28:                     CurrentRequestVersion.set(key.getVersion());
 29:                     Value cacheValue = readWriteCacheMap.get(key);
 30:                     Value currentCacheValue = readOnlyCacheMap.get(key);
 31:                     if (cacheValue != currentCacheValue) { // 不一致时,进行替换
 32:                         readOnlyCacheMap.put(key, cacheValue);
 33:                     }
 34:                 } catch (Throwable th) {
 35:                     logger.error("Error while updating the client cache from response cache for key {}", key.toStringCompact(), th);
 36:                 }
 37:             }
 38:         }
 39:     };
 40: }
复制代码
  • 第 7 至 12 行 :初始化定时任务。配置 eureka.responseCacheUpdateIntervalMs,设置任务执行频率,默认值 :30 * 1000 毫秒。
  • 第 17 至 39 行 :创建定时任务。
    • 第 22 行 :循环 readOnlyCacheMap 的缓存键。为什么不循环 readWriteCacheMapreadOnlyCacheMap 的缓存过期依赖 readWriteCacheMap,因此缓存键会更多。
    • 第 28 行 至 33 行 :对比 readWriteCacheMapreadOnlyCacheMap 的缓存值,若不一致,以前者为主。通过这样的方式,实现了 readOnlyCacheMap 的定时过期。

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