org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
  org.springframework.cloud.netflix.eureka.server.EurekaServerAutoConfiguration

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Import(EurekaServerMarkerConfiguration.class)
public @interface EnableEurekaServer {
}

@Configuration(proxyBeanMethods = false)
@Import(EurekaServerInitializerConfiguration.class)
@ConditionalOnBean(EurekaServerMarkerConfiguration.Marker.class)
@EnableConfigurationProperties({ EurekaDashboardProperties.class,
        InstanceRegistryProperties.class })
@PropertySource("classpath:/eureka/server.properties")
public class EurekaServerAutoConfiguration implements WebMvcConfigurer {
    ......
}

@Configuration(proxyBeanMethods = false)
public class EurekaServerInitializerConfiguration
        implements ServletContextAware, SmartLifecycle, Ordered {
    ......
}
    

EurekaServerInitializerConfiguration#start()
    EurekaServerBoostrap#contextInitialized(ServletContext context)
        EurekaServerBoostrap#initEurekaServerContext()
            // Copy registry from neighboring eureka node  此处进行复制相邻eureka注册表的操作
            int registryCount = this.registry.syncUp();

@Bean
@ConditionalOnMissingBean
public EurekaServerContext eurekaServerContext(ServerCodecs serverCodecs,
        PeerAwareInstanceRegistry registry, PeerEurekaNodes peerEurekaNodes) {
    return new DefaultEurekaServerContext(this.eurekaServerConfig, serverCodecs,
            registry, peerEurekaNodes, this.applicationInfoManager);
}

@PostConstruct
@Override
public void initialize() {
    logger.info("Initializing ...");
    //启动一个只拥有一个线程的线程池，第一次进去会更新一下集群其他节点信息。
    peerEurekaNodes.start();
    try {
    //调用PeerAwareInstanceRegistryImpl的init方法
        registry.init(peerEurekaNodes);
    } catch (Exception e) {
        throw new RuntimeException(e);
    }
    logger.info("Initialized");
}

@POST
@Consumes({"application/json", "application/xml"})
public Response addInstance(InstanceInfo info,
                            @HeaderParam(PeerEurekaNode.HEADER_REPLICATION) String isReplication) {
    ......
     //registry是PeerAwareInstanceRegistry类型
    registry.register(info, "true".equals(isReplication));
    ......
}

@PUT
public Response renewLease(
            @HeaderParam(PeerEurekaNode.HEADER_REPLICATION) String isReplication,
            @QueryParam("overriddenstatus") String overriddenStatus,
            @QueryParam("status") String status,
            @QueryParam("lastDirtyTimestamp") String lastDirtyTimestamp) {
    ......
    boolean isSuccess = registry.renew(app.getName(), id, isFromReplicaNode);
    ......
}

public boolean renew(String appName, String id, boolean isReplication) {
        RENEW.increment(isReplication);
     //根据appName获取服务集群的租约集合
        Map<String, Lease<InstanceInfo>> gMap = registry.get(appName);
        Lease<InstanceInfo> leaseToRenew = null;
        if (gMap != null) {
            leaseToRenew = gMap.get(id);
        }
        if (leaseToRenew == null) {
            RENEW_NOT_FOUND.increment(isReplication);
            logger.warn("DS: Registry: lease doesn't exist, registering resource: {} - {}", appName, id);
            return false;
        } else {
            InstanceInfo instanceInfo = leaseToRenew.getHolder();
            if (instanceInfo != null) {
                // touchASGCache(instanceInfo.getASGName());
                //查看服务实例状态
                InstanceStatus overriddenInstanceStatus = this.getOverriddenInstanceStatus(
                        instanceInfo, leaseToRenew, isReplication);
                if (overriddenInstanceStatus == InstanceStatus.UNKNOWN) {
                    logger.info("Instance status UNKNOWN possibly due to deleted override for instance {}"
                            + "; re-register required", instanceInfo.getId());
                    RENEW_NOT_FOUND.increment(isReplication);
                    return false;
                }
                if (!instanceInfo.getStatus().equals(overriddenInstanceStatus)) {
                    logger.info(
                            "The instance status {} is different from overridden instance status {} for instance {}. "
                                    + "Hence setting the status to overridden status", instanceInfo.getStatus().name(),
                                    instanceInfo.getOverriddenStatus().name(),
                                    instanceInfo.getId());
                    instanceInfo.setStatusWithoutDirty(overriddenInstanceStatus);

                }
            }
             //统计每分钟续租次数
            renewsLastMin.increment();
             //更新租约
            leaseToRenew.renew();
            return true;
        }
    }

//isLeaseExpirationEnabled在
public boolean isLeaseExpirationEnabled在() {
    if (!isSelfPreservationModeEnabled()) {
        //此处获取自我保护模式开关状态，最终对应于EurekaServerConfigBean类中的enableSelfPreservation配置项，
        // The self preservation mode is disabled, hence allowing the instances to expire.
        return true;
    }
    return numberOfRenewsPerMinThreshold > 0 && getNumOfRenewsInLastMin() > numberOfRenewsPerMinThreshold;
}

public void evict(long additionalLeaseMs) {
    logger.debug("Running the evict task");

    if (!isLeaseExpirationEnabled()) {
        logger.debug("DS: lease expiration is currently disabled.");
        return;
    }

    // We collect first all expired items, to evict them in random order. For large eviction sets,
    // if we do not that, we might wipe out whole apps before self preservation kicks in. By randomizing it,
    // the impact should be evenly distributed across all applications.
    List<Lease<InstanceInfo>> expiredLeases = new ArrayList<>();
    /*
    遍历注册表register，依次判断租约是否过期。一次性获取所有的过期租约。
    */
    for (Entry<String, Map<String, Lease<InstanceInfo>>> groupEntry : registry.entrySet()) {
        Map<String, Lease<InstanceInfo>> leaseMap = groupEntry.getValue();
        if (leaseMap != null) {
            for (Entry<String, Lease<InstanceInfo>> leaseEntry : leaseMap.entrySet()) {
                Lease<InstanceInfo> lease = leaseEntry.getValue();
                if (lease.isExpired(additionalLeaseMs) && lease.getHolder() != null) {
                    expiredLeases.add(lease);
                }
            }
        }
    }

    // To compensate for GC pauses or drifting local time, we need to use current registry size as a base for
    // triggering self-preservation. Without that we would wipe out full registry.
    //获取注册表租约总数
    int registrySize = (int) getLocalRegistrySize();
    //计算注册表租约的阈值 （总数乘以 续租百分比），得出要续租的数量
    int registrySizeThreshold = (int) (registrySize * serverConfig.getRenewalPercentThreshold());
    //总数减去要续租的数量，就是理论要剔除的数量        
    int evictionLimit = registrySize - registrySizeThreshold;
    //求 上面理论剔除数量，和过期租约总数的最小值。就是最终要提出的数量。
    int toEvict = Math.min(expiredLeases.size(), evictionLimit);
    if (toEvict > 0) {
        logger.info("Evicting {} items (expired={}, evictionLimit={})", toEvict, expiredLeases.size(), evictionLimit);

        Random random = new Random(System.currentTimeMillis());
        for (int i = 0; i < toEvict; i++) {
            // Pick a random item (Knuth shuffle algorithm)
            int next = i + random.nextInt(expiredLeases.size() - i);
            Collections.swap(expiredLeases, i, next);
            Lease<InstanceInfo> lease = expiredLeases.get(i);

            String appName = lease.getHolder().getAppName();
            String id = lease.getHolder().getId();
            EXPIRED.increment();
            logger.warn("DS: Registry: expired lease for {}/{}", appName, id);
            //执行 服务下线将服务从注册表清除掉。
            internalCancel(appName, id, false);
        }
    }
}

EurekaServerInitializerConfiguration#start()
    eurekaServerBootstrap.contextInitialized(EurekaServerInitializerConfiguration.this.servletContext);
        EurekaServerBoostrap#initEurekaServerContext()
            registry.openForTraffic(this.applicationInfoManager, registryCount);
                PeerAwareInstanceRegistryImpl#openForTraffic
                    AbstractInstanceRegistry#postInit()

@DELETE
public Response cancelLease(
        @HeaderParam(PeerEurekaNode.HEADER_REPLICATION) String isReplication) {
    ......
    boolean isSuccess = registry.cancel(app.getName(), id, "true".equals(isReplication));
    ......
}

InstanceResource#cancelLease
    PeerAwareInstanceRegistryImpl#cancel //此方法中还有将取消操作复制给其他eureka节点的逻辑
        AbstractInstanceRegistry#cancel
            AbstractInstanceRegistry#internalCancel

protected boolean internalCancel(String appName, String id, boolean isReplication) {
    try {
        //先获取读锁，防止被其他线程修改
        read.lock();
        CANCEL.increment(isReplication);
        //根据appName获取服务实例集群。
        Map<String, Lease<InstanceInfo>> gMap = registry.get(appName);
        Lease<InstanceInfo> leaseToCancel = null;
        //  在内存中取消实例 id的服务
        if (gMap != null) {
            leaseToCancel = gMap.remove(id);
        }
        //添加到最近下线服务的统计队列
        recentCanceledQueue.add(new Pair<Long, String>(System.currentTimeMillis(), appName + "(" + id + ")"));
        InstanceStatus instanceStatus = overriddenInstanceStatusMap.remove(id);
        if (instanceStatus != null) {
            logger.debug("Removed instance id {} from the overridden map which has value {}", id, instanceStatus.name());
        }
        // 往下判断leaseToCancel是否为空，租约不存在，返回false
        if (leaseToCancel == null) {
            CANCEL_NOT_FOUND.increment(isReplication);
            logger.warn("DS: Registry: cancel failed because Lease is not registered for: {}/{}", appName, id);
            return false;
        } else {
            //若存在，设置租约下线时间
            leaseToCancel.cancel();
            InstanceInfo instanceInfo = leaseToCancel.getHolder();
            String vip = null;
            String svip = null;
            if (instanceInfo != null) {
                //获取持有租约的服务信息，标记服务实例为instanceInfo.setActionType(ActionType.DELETED);
                instanceInfo.setActionType(ActionType.DELETED);
                //添加到租约变更记录队列
                recentlyChangedQueue.add(new RecentlyChangedItem(leaseToCancel));//用于eureka client的增量拉取注册表信息。
                instanceInfo.setLastUpdatedTimestamp();
                vip = instanceInfo.getVIPAddress();
                svip = instanceInfo.getSecureVipAddress();
            }
            invalidateCache(appName, vip, svip);
            logger.info("Cancelled instance {}/{} (replication={})", appName, id, isReplication);
        }
    } finally {
        read.unlock();
    }

    synchronized (lock) {
        if (this.expectedNumberOfClientsSendingRenews > 0) {
            // Since the client wants to cancel it, reduce the number of clients to send renews.
            this.expectedNumberOfClientsSendingRenews = this.expectedNumberOfClientsSendingRenews - 1;
            updateRenewsPerMinThreshold();
        }
    }

    return true;
}

EurekaServerInitializerConfiguration#start()
    eurekaServerBootstrap.contextInitialized(...)
        EurekaServerBootstrap#initEurekaServerContext()
            PeerAwareInstanceRegistryImpl#syncUp();

public int syncUp() {
        // Copy entire entry from neighboring DS node
        int count = 0;

        for (int i = 0; ((i < serverConfig.getRegistrySyncRetries()) && (count == 0)); i++) {
            if (i > 0) {
                try {
                    Thread.sleep(serverConfig.getRegistrySyncRetryWaitMs());
                } catch (InterruptedException e) {
                    logger.warn("Interrupted during registry transfer..");
                    break;
                }
            }
            Applications apps = eurekaClient.getApplications();
            for (Application app : apps.getRegisteredApplications()) {
                for (InstanceInfo instance : app.getInstances()) {
                    try {
                        if (isRegisterable(instance)) {
                            register(instance, instance.getLeaseInfo().getDurationInSecs(), true);
                            count++;
                        }
                    } catch (Throwable t) {
                        logger.error("During DS init copy", t);
                    }
                }
            }
        }
        return count;
    }

。。。
// Copy registry from neighboring eureka node
int registryCount = this.registry.syncUp();
this.registry.openForTraffic(this.applicationInfoManager, registryCount);
。。。

public void openForTraffic(ApplicationInfoManager applicationInfoManager, int count) {
    // Renewals happen every 30 seconds and for a minute it should be a factor of 2.
    this.expectedNumberOfClientsSendingRenews = count;
    updateRenewsPerMinThreshold();
    logger.info("Got {} instances from neighboring DS node", count);
    logger.info("Renew threshold is: {}", numberOfRenewsPerMinThreshold);
    this.startupTime = System.currentTimeMillis();
    //如果count=0，没有拉取到注册表信息，将此值设为true，表示其他peer来取空的实例信息，意味着，将不允许client从此server获取注册表信息。如果count>0，将此值设置为false，允许client来获取注册表。   
    if (count > 0) {
        this.peerInstancesTransferEmptyOnStartup = false;
    }
    DataCenterInfo.Name selfName = applicationInfoManager.getInfo().getDataCenterInfo().getName();
    boolean isAws = Name.Amazon == selfName;
    if (isAws && serverConfig.shouldPrimeAwsReplicaConnections()) {
        logger.info("Priming AWS connections for all replicas..");
        primeAwsReplicas(applicationInfoManager);
    }
    logger.info("Changing status to UP");
    applicationInfoManager.setInstanceStatus(InstanceStatus.UP);
    super.postInit();
}

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();
        }
    }

//示例：PeerEurekaNode
public void cancel(final String appName, final String id) throws Exception {
    long expiryTime = System.currentTimeMillis() + maxProcessingDelayMs;
    batchingDispatcher.process(
        taskId("cancel", appName, id),
        new InstanceReplicationTask(targetHost, Action.Cancel, appName, id) {
            @Override
            public EurekaHttpResponse<Void> execute() {
                return replicationClient.cancel(appName, id);
            }

            @Override
            public void handleFailure(int statusCode, Object responseEntity) throws Throwable {
                super.handleFailure(statusCode, responseEntity);
                if (statusCode == 404) {
                    logger.warn("{}: missing entry.", getTaskName());
                }
            }
        },
        expiryTime
    );
}

@ConditionalOnBean         //   当给定的在bean存在时,则实例化当前Bean
@ConditionalOnMissingBean  //   当给定的在bean不存在时,则实例化当前Bean
@ConditionalOnClass        //   当给定的类名在类路径上存在，则实例化当前Bean
@ConditionalOnMissingClass //   当给定的类名在类路径上不存在，则实例化当前Bean

//服务注册相关
boolean register()
void unregister()

//服务续约
boolean renew()

//关闭eureka client
public synchronized void shutdown()

//检查当前client状态，当client状态发生变化时，将会触发新的注册事件，去更新eureka server的注册表中的服务实例信息。
public void registerHealthCheck(HealthCheckHandler healthCheckHandler)

//注册事件监听器，当实例信息有变时，触发对应的处理事件。
public void registerEventListener(EurekaEventListener eventListener)

DiscoveryClient(ApplicationInfoManager applicationInfoManager, EurekaClientConfig config, AbstractDiscoveryClientOptionalArgs args, Provider<BackupRegistry> backupRegistryProvider, EndpointRandomizer endpointRandomizer) {
      ......
      //shouldFetchRegistry，其实现类为EurekaClientConfigBean，找到它其实对应于：eureka.client.fetch-register，true：表示client从server拉取注册表信息。
     if (config.shouldFetchRegistry()) {
         this.registryStalenessMonitor = new ThresholdLevelsMetric(this, METRIC_REGISTRY_PREFIX + "lastUpdateSec_", new long[]{15L, 30L, 60L, 120L, 240L, 480L});
     } else {
         this.registryStalenessMonitor = ThresholdLevelsMetric.NO_OP_METRIC;
     }
    
    //shouldRegisterWithEureka，点其实现类EurekaClientConfigBean，找到它其实对应于：eureka.client.register-with-eureka：true：表示client将注册到server。
    if (config.shouldRegisterWithEureka()) {
        this.heartbeatStalenessMonitor = new ThresholdLevelsMetric(this, METRIC_REGISTRATION_PREFIX + "lastHeartbeatSec_", new long[]{15L, 30L, 60L, 120L, 240L, 480L});
    } else {
        this.heartbeatStalenessMonitor = ThresholdLevelsMetric.NO_OP_METRIC;
    }
    ......
        
// default size of 2 - 1 each for heartbeat and cacheRefresh
    scheduler = Executors.newScheduledThreadPool(2,
                                                     new ThreadFactoryBuilder()
                                                     .setNameFormat("DiscoveryClient-%d")
                                                     .setDaemon(true)
                                                     .build());
    //用于发送心跳
    heartbeatExecutor = new ThreadPoolExecutor(
        1, clientConfig.getHeartbeatExecutorThreadPoolSize(), 0, TimeUnit.SECONDS,
        new SynchronousQueue<Runnable>(),
        new ThreadFactoryBuilder()
        .setNameFormat("DiscoveryClient-HeartbeatExecutor-%d")
        .setDaemon(true)
        .build()
    );  // use direct handoff
    //用于刷新缓存
    cacheRefreshExecutor = new ThreadPoolExecutor(
        1, clientConfig.getCacheRefreshExecutorThreadPoolSize(), 0, TimeUnit.SECONDS,
        new SynchronousQueue<Runnable>(),
        new ThreadFactoryBuilder()
        .setNameFormat("DiscoveryClient-CacheRefreshExecutor-%d")
        .setDaemon(true)
        .build()
    );  // use direct handoff
    
    //eurekaTransport是eureka Client和eureka server进行http交互jersey客户端。点开EurekaTransport，看到许多httpclient相关的属性。
    eurekaTransport = new EurekaTransport();
    
    if (clientConfig.shouldFetchRegistry()) {
        ....
            //从eureka server拉取注册表中的信息，将注册表缓存到本地，可以就近获取其他服务信息，减少于server的交互。
         boolean primaryFetchRegistryResult = fetchRegistry(false);
         ......
    }
    
    //register()进行注册，若注册失败则抛出异常
    if (clientConfig.shouldRegisterWithEureka() && clientConfig.shouldEnforceRegistrationAtInit()) {
        try {
            if (!register() ) {
                throw new IllegalStateException("Registration error at startup. Invalid server response.");
            }
        } catch (Throwable th) {
            logger.error("Registration error at startup: {}", th.getMessage());
            throw new IllegalStateException(th);
        }
    }
    
    //启动调度任务
    initScheduledTasks();
}

如果增量式拉取被禁止或第一次拉取注册表，则进行全量拉取：getAndStoreFullRegistry()。
否则进行增量拉取注册表信息getAndUpdateDelta(applications)。
一般情况，在Eureka client第一次启动，会进行全量拉取。之后的拉取都尽量尝试只进行增量拉取。

  拉取服务注册表：
  全量拉取：getAndStoreFullRegistry();
  增量拉取：getAndUpdateDelta(applications);

进入getAndStoreFullRegistry() 方法，有一方法：eurekaTransport.queryClient.getApplications。
  通过debug发现 实现类是AbstractJerseyEurekaHttpClient，点开，debug出 
  webResource 地址为：`http://root:root@eureka-7900:7900/eureka/apps/`，此端点用于获取 server 中所有的注册表信息。
  getAndStoreFullRegistry()可能被多个线程同时调用，导致新拉取的注册表被旧的覆盖(如果新拉取的动作设置apps阻塞的情况下）。
  此时用了AutomicLong来进行版本管理，如果更新时版本不一致，不保存apps。
  通过这个判断fetchRegistryGeneration.compareAndSet(currentUpdateGeneration, currentUpdateGeneration + 1)，如果版本一致，并设置新版本（+1），
  接着执行localRegionApps.set(this.filterAndShuffle(apps));过滤并洗牌apps。点开this.filterAndShuffle(apps)实现，继续点apps.shuffleAndIndexInstances，继续点shuffleInstances，继续点application.shuffleAndStoreInstances，继续点_shuffleAndStoreInstances，发现if (filterUpInstances && InstanceStatus.UP != instanceInfo.getStatus())。只保留状态为UP的服务。

回到刚才的fetchRegistry方法中，getAndUpdateDelta，增量拉取。通过getDelta方法，看到实际拉取的地址是：apps/delta，如果获取到的delta为空，则全量拉取。
  通常来讲是3分钟之内注册表的信息变化（在server端判断），获取到delta后，会更新本地注册表。
  增量式拉取是为了维护client和server端 注册表的一致性，防止本地数据过久，而失效，采用增量式拉取的方式，减少了client和server的通信量。
  client有一个注册表缓存刷新定时器，专门负责维护两者之间的信息同步，但是当增量出现意外时，定时器将执行，全量拉取以更新本地缓存信息。更新本地注册表方法updateDelta，有一个细节。
  if (ActionType.ADDED.equals(instance.getActionType())) ，public enum ActionType {
          ADDED, // Added in the discovery server
          MODIFIED, // Changed in the discovery server
          DELETED
          // Deleted from the discovery server
      }，
  在InstanceInfo instance中有一个instance.getActionType()，ADDED和MODIFIED状态的将更新本地注册表applications.addApplication，DELETED将从本地剔除掉existingApp.removeInstance(instance)。

DiscoveryClient构造函数中，拉取fetchRegistry完后进行register注册。由于构造函数开始时已经将服务实例元数据封装好了instanceInfo，所以此处之间向server发送instanceInfo，
通过方法httpResponse = eurekaTransport.registrationClient.register(instanceInfo);看到String urlPath = "apps/" + info.getAppName();又是一个server端点，退上去f7，httpResponse.getStatusCode() == Status.NO_CONTENT.getStatusCode();204状态码，则注册成功。

A scheduler to be used for the following 3 tasks:
- updating service urls
- scheduling a TimedSuperVisorTask。

//心跳定时任务
  new TimedSupervisorTask(
                              "heartbeat",
                              scheduler,
                              heartbeatExecutor,
                              renewalIntervalInSecs,
                              TimeUnit.SECONDS,
                              expBackOffBound,
                              new HeartbeatThread())
  //HeartbeatThread线程内部run方法定义如下：
class CacheRefreshThread implements Runnable{
    public void run() {
        if (renew()) {
            lastSuccessfulHeartbeatTimestamp = System.currentTimeMillis();
        }
    }
}

  
//缓存定时任务
  scheduler.schedule(
                      new TimedSupervisorTask(
                              "cacheRefresh",
                              scheduler,
                              cacheRefreshExecutor,
                              registryFetchIntervalSeconds,
                              TimeUnit.SECONDS,
                              expBackOffBound,
                              new CacheRefreshThread()
                      ),
 //CacheRefreshThread线程内部run方法定义如下：
class CacheRefreshThread implements Runnable {
          public void run() {
              refreshRegistry();
          }
      }

//还有一个定时任务，按需注册。当instanceinfo和status发生变化时，需要向server同步，去更新自己在server中的实例信息。保证server注册表中服务实例信息的有效和可用。
  // InstanceInfo replicator
          instanceInfoReplicator = new InstanceInfoReplicator(
                  this,
                  instanceInfo,
                  clientConfig.getInstanceInfoReplicationIntervalSeconds(),
                  2); // burstSize
  
          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();
              }
          };
          if (clientConfig.shouldOnDemandUpdateStatusChange()) {
              applicationInfoManager.registerStatusChangeListener(statusChangeListener);
          }
      instanceInfoReplicator.start(clientConfig.getInitialInstanceInfoReplicationIntervalSeconds());    
      

//此定时任务有2个部分，
//  1：定时刷新服务实例信息和检查应用状态的变化，在服务实例信息发生改变的情况下向server重新发起注册。InstanceInfoReplicator点进去。看到一个方法    
  
  public void run() {
          try {
              discoveryClient.refreshInstanceInfo();//刷新instanceinfo。
            //如果实例信息有变，返回数据更新时间。
              Long dirtyTimestamp = instanceInfo.isDirtyWithTime();
              if (dirtyTimestamp != null) {
                  discoveryClient.register();//注册服务实例。
                  instanceInfo.unsetIsDirty(dirtyTimestamp);
              }
          } catch (Throwable t) {
              logger.warn("There was a problem with the instance info replicator", t);
          } finally {
          //延时执行下一个检查任务。用于再次调用run方法，继续检查服务实例信息和状态的变化。
              Future next = scheduler.schedule(this, replicationIntervalSeconds, TimeUnit.SECONDS);
              scheduledPeriodicRef.set(next);
          }
      }      

refreshInstanceInfo点进去，看方法注释：如果有变化，在下次心跳时，同步向server。

//2.注册状态改变监听器，在应用状态发生变化时，刷新服务实例信息，在服务实例信息发生改变时向server注册。  看这段            
   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();
              }
          };如果状态发生改变，调用onDemandUpdate（），点onDemandUpdate进去，看到InstanceInfoReplicator.this.run();     
          
//总结：两部分，一部分自己去检查，一部分等待状态监听事件。

//初始化定时任务完成，最后一步启动步骤完成。接下来就是正常服务于业务。然后消亡。          

//此方法上有一个注解，表示：在销毁前执行此方法。unregisterStatusChangeListener注销监听器。
@PreDestroy
@Override
public synchronized void shutdown() {
    ......
        //取消定时任务。
    cancelScheduledTasks();
    ......
    //服务下线。
    unregister();
    //关闭jersy客户端  
    eurekaTransport.shutdown();
    //其他操作
    ......
} 

unregister点进去。cancel点进去。AbstractJerseyEurekaHttpClient。String urlPath = "apps/" + appName + '/' + id;看到url和http请求delete方法。      

org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
org.springframework.cloud.netflix.eureka.config.EurekaClientConfigServerAutoConfiguration,\
org.springframework.cloud.netflix.eureka.config.EurekaDiscoveryClientConfigServiceAutoConfiguration,\
org.springframework.cloud.netflix.eureka.EurekaClientAutoConfiguration,\
org.springframework.cloud.netflix.ribbon.eureka.RibbonEurekaAutoConfiguration,\
org.springframework.cloud.netflix.eureka.EurekaDiscoveryClientConfiguration,\
org.springframework.cloud.netflix.eureka.reactive.EurekaReactiveDiscoveryClientConfiguration,\
org.springframework.cloud.netflix.eureka.loadbalancer.LoadBalancerEurekaAutoConfiguration

org.springframework.cloud.bootstrap.BootstrapConfiguration=\
org.springframework.cloud.netflix.eureka.config.EurekaDiscoveryClientConfigServiceBootstrapConfiguration

@ConditionalOnClass(ConfigServicePropertySourceLocator.class)
@ConditionalOnProperty(value = "spring.cloud.config.discovery.enabled",
        matchIfMissing = false)
@Configuration(proxyBeanMethods = false)
@Import({ EurekaDiscoveryClientConfiguration.class, // this emulates
        // @EnableDiscoveryClient, the import
        // selector doesn't run before the
        // bootstrap phase
        EurekaClientAutoConfiguration.class,
        EurekaReactiveDiscoveryClientConfiguration.class,
        ReactiveCommonsClientAutoConfiguration.class })
public class EurekaDiscoveryClientConfigServiceBootstrapConfiguration {
}

CloudEurekaClient cloudEurekaClient = new CloudEurekaClient(appManager,
                    config, this.optionalArgs, this.context);

public class CloudEurekaClient extends DiscoveryClient {
    ......
}

/*
根据接口类获取其实现类的实例，这个方法返回的是对象列表。
Load and instantiate the factory implementations of the given type from "META-INF/spring.factories", using the given class loader.
The returned factories are sorted through AnnotationAwareOrderComparator.
If a custom instantiation strategy is required, use loadFactoryNames(java.lang.Class<?>, java.lang.ClassLoader) to obtain all registered factory names.
*/
public static <T> List<T> loadFactories(Class<T> factoryType, @Nullable ClassLoader classLoader)

/*
根据接口获取其接口类的名称，这个方法返回的是类名的列表。
Load the fully qualified class names of factory implementations of the given type from "META-INF/spring.factories", using the given class loader.
*/
public static List<String> loadFactoryNames(Class<?> factoryType, @Nullable ClassLoader classLoader)