咱们从上面的图能够看出，作为一个client端，他有以下性能：
- Register（服务注册）：向Eureka Server注册本身的信息，比方IP地址、端口等。
- Renew（服务续约）：服务启动后，每隔30秒会向Eureka Server发送心跳进行服务续约。
- Get（服务发现）：获取向Eureka Server注册的服务列表，并缓存本地，默认30秒。
- Cancel（服务下线）：向Eureka Server发送下线信息，Eureka Server会把这个服务标记为下线。
服务启动
springboot的主动拆卸读取Eureka Client的spring.factories文件，咱们看到他外面有多个EnableAutoConfiguration，次要的类是EurekaClientAutoConfiguration。EurekaClientAutoConfiguration类中有多个bean的加载，咱们先看看EurekaInstanceConfigBean的加载。
EurekaInstanceConfigBean
EurekaInstanceConfigBean有个@ConfigurationProperties("eureka.instance")注解，所以咱们在配置文件里写的eureka.instance.instanceId这类的信息最终都在赋值给这个类。还有比拟重要的leaseRenewalIntervalInSeconds续约频率（默认每30秒）、leaseExpirationDurationInSeconds续约过期工夫（默认90秒）都是在这个类配置的。
@Bean@ConditionalOnMissingBean(value = EurekaInstanceConfig.class, search = SearchStrategy.CURRENT)public EurekaInstanceConfigBean eurekaInstanceConfigBean(InetUtils inetUtils, ManagementMetadataProvider managementMetadataProvider) { // 省略局部代码 EurekaInstanceConfigBean instance = new EurekaInstanceConfigBean(inetUtils); // 省略局部代码 return instance;}ApplicationInfoManager
ApplicationInfoManager也是在EurekaClientAutoConfiguration类中。
创立eurekaApplicationInfoManager对象的时候，会先创立InstanceInfo对象，InstanceInfo对象的值大部分是从EurekaInstanceConfig复制过去的，另外租约信息是寄存在InstanceInfo的leaseInfo中。
所以初始化ApplicationInfoManager的时候，就是赋值EurekaInstanceConfig和InstanceInfo。
@Bean@ConditionalOnMissingBean(value = ApplicationInfoManager.class, search = SearchStrategy.CURRENT)@org.springframework.cloud.context.config.annotation.RefreshScope@Lazypublic ApplicationInfoManager eurekaApplicationInfoManager( EurekaInstanceConfig config) { InstanceInfo instanceInfo = new InstanceInfoFactory().create(config); return new ApplicationInfoManager(config, instanceInfo);}EurekaClientConfigBean
EurekaClientConfigBean也是一个配置信息的bean，他次要是EurekaClient和EurekaServer相干的信息，比方EurekaServer的地址defaultZone、是否从注册核心拉取注册信息fetchRegistry（默认true），拉取的频率registryFetchIntervalSeconds（默认每30秒）、是否向注册核心注册registerWithEureka（默认true）等。
@Bean@ConditionalOnMissingBean(value = EurekaClientConfig.class, search = SearchStrategy.CURRENT)public EurekaClientConfigBean eurekaClientConfigBean(ConfigurableEnvironment env) { return new EurekaClientConfigBean();}EurekaClient
创立一个EurekaClient类，这个类就是负责服务的注册、续约、勾销、获取注册列表。
@Bean(destroyMethod = "shutdown")@ConditionalOnMissingBean(value = EurekaClient.class, search = SearchStrategy.CURRENT)@org.springframework.cloud.context.config.annotation.RefreshScope@Lazypublic EurekaClient eurekaClient(ApplicationInfoManager manager, EurekaClientConfig config, EurekaInstanceConfig instance, @Autowired(required = false) HealthCheckHandler healthCheckHandler) { ApplicationInfoManager appManager; if (AopUtils.isAopProxy(manager)) { appManager = ProxyUtils.getTargetObject(manager); } else { appManager = manager; } CloudEurekaClient cloudEurekaClient = new CloudEurekaClient(appManager, config, this.optionalArgs, this.context); cloudEurekaClient.registerHealthCheck(healthCheckHandler); return cloudEurekaClient;}联合下面几个类的加载以及EurekaClient的加载，咱们能够晓得这几个类的关系如下：
在DiscoveryClient的构造函数里，次要是初始化一些配置参数，以及为拉取注册表信息、初始化定时工作。
@InjectDiscoveryClient(ApplicationInfoManager applicationInfoManager, EurekaClientConfig config, AbstractDiscoveryClientOptionalArgs args, Provider<BackupRegistry> backupRegistryProvider, EndpointRandomizer endpointRandomizer) { // 初始化applicationInfoManager、config等略 try { // 创立外围数为2的线程池，一个用于heartbeat，一个用于cacheRefresh // default size of 2 - 1 each for heartbeat and cacheRefresh scheduler = Executors.newScheduledThreadPool(2, new ThreadFactoryBuilder() .setNameFormat("DiscoveryClient-%d") .setDaemon(true) .build()); heartbeatExecutor = new ThreadPoolExecutor( 1, clientConfig.getHeartbeatExecutorThreadPoolSize(), 0, TimeUnit.SECONDS, new SynchronousQueue<Runnable>(), new ThreadFactoryBuilder() .setNameFormat("DiscoveryClient-HeartbeatExecutor-%d") .setDaemon(true) .build() ); // use direct handoff cacheRefreshExecutor = new ThreadPoolExecutor( 1, clientConfig.getCacheRefreshExecutorThreadPoolSize(), 0, TimeUnit.SECONDS, new SynchronousQueue<Runnable>(), new ThreadFactoryBuilder() .setNameFormat("DiscoveryClient-CacheRefreshExecutor-%d") .setDaemon(true) .build() ); // use direct handoff // 与EurekaServer网络通信用的 eurekaTransport = new EurekaTransport(); scheduleServerEndpointTask(eurekaTransport, args); //其余的略 } catch (Throwable e) { throw new RuntimeException("Failed to initialize DiscoveryClient!", e); } if (clientConfig.shouldFetchRegistry()) { try { // 拉取注册表信息 boolean primaryFetchRegistryResult = fetchRegistry(false); //其余的略，没有拉取胜利从备份注册核心获取 } } //其余的略 // 初始化定时工作 initScheduledTasks(); //其余的略}initScheduledTasks，用来开启更新服务注册列表和续租的定时工作，以及对EurekaServer的注册。
private void initScheduledTasks() { if (clientConfig.shouldFetchRegistry()) { // registry cache refresh timer // 这个定时工作是更新服务注册列表 // 更新频率 int registryFetchIntervalSeconds = clientConfig.getRegistryFetchIntervalSeconds(); // 提早最大乘数，比方更新频率是5s，那最大延迟时间就是50s，这个前面讲线程的时候会具体说 int expBackOffBound = clientConfig.getCacheRefreshExecutorExponentialBackOffBound(); cacheRefreshTask = new TimedSupervisorTask( "cacheRefresh", scheduler, cacheRefreshExecutor, registryFetchIntervalSeconds, TimeUnit.SECONDS, expBackOffBound, new CacheRefreshThread() ); scheduler.schedule( cacheRefreshTask, registryFetchIntervalSeconds, TimeUnit.SECONDS); } instanceInfoReplicator = new InstanceInfoReplicator( this, instanceInfo, clientConfig.getInstanceInfoReplicationIntervalSeconds(), 2); if (clientConfig.shouldRegisterWithEureka()) { // 这个定时工作是续租 // 续约频率 int renewalIntervalInSecs = instanceInfo.getLeaseInfo().getRenewalIntervalInSecs(); int expBackOffBound = clientConfig.getHeartbeatExecutorExponentialBackOffBound(); logger.info("Starting heartbeat executor: " + "renew interval is: {}", renewalIntervalInSecs); // Heartbeat timer heartbeatTask = new TimedSupervisorTask( "heartbeat", scheduler, heartbeatExecutor, renewalIntervalInSecs, TimeUnit.SECONDS, expBackOffBound, new HeartbeatThread() ); scheduler.schedule( heartbeatTask, renewalIntervalInSecs, TimeUnit.SECONDS); // 其余的略 // 注册到注册核心 instanceInfoReplicator.start(clientConfig.getInitialInstanceInfoReplicationIntervalSeconds()); } else { logger.info("Not registering with Eureka server per configuration"); }}好了，以上对EurekaServer的注册、续租、注册表获取都提及到了，前面再具体的解说这些内容。