Eureka的源码解析

EnableEurekaServer注解作用
通过 @EnableEurekaServer 激活EurekaServer

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

}

此类有一个重要作用：导入EurekaServerMarkerConfiguration配置类实例化了一个Marker的bean对
象，此对象是实例化核心配置类的前提条件

/**
 * Responsible for adding in a marker bean to activate
 * {@link EurekaServerAutoConfiguration}
 *
 * @author Biju Kunjummen
 */
@Configuration
public class EurekaServerMarkerConfiguration {

    @Bean
    public Marker eurekaServerMarkerBean() {
        return new Marker();
    }

    class Marker {
    }
}

自动装载核心配置类
SpringCloud对EurekaServer的封装使得发布一个EurekaServer无比简单，根据自动装载原则可以在
spring-cloud-netflix-eureka-server-2.1.0.RELEASE.jar 下找到 spring.factories

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

@Configuration
@Import(EurekaServerInitializerConfiguration.class)
@ConditionalOnBean(EurekaServerMarkerConfiguration.Marker.class)
@EnableConfigurationProperties({ EurekaDashboardProperties.class,
        InstanceRegistryProperties.class })
@PropertySource("classpath:/eureka/server.properties")
public class EurekaServerAutoConfiguration extends WebMvcConfigurerAdapter {
    /**
     * List of packages containing Jersey resources required by the Eureka server
     */
    private static final String[] EUREKA_PACKAGES = new String[] { "com.netflix.discovery",
            "com.netflix.eureka" };

    @Autowired
    private ApplicationInfoManager applicationInfoManager;

    @Autowired
    private EurekaServerConfig eurekaServerConfig;

    @Autowired
    private EurekaClientConfig eurekaClientConfig;

    @Autowired
    private EurekaClient eurekaClient;

现在我们展开来说这个Eureka服务端的自动配置类;
1. 这个配置类实例化的前提条件是上下文中存在 EurekaServerMarkerConfiguration.Marker 这个
bean,解释了上面的问题

2. 通过@EnableConfigurationProperties({ EurekaDashboardProperties.class,InstanceRegistryProperties.class })导入了两个配置类
1. EurekaDashboardProperties ： 配置 EurekaServer的管控台
2. InstanceRegistryProperties ： 配置期望续约数量和默认的通信数量
3. 通过@Import({EurekaServerInitializerConfiguration.class})引入启动配置类

EurekaServerInitializerConfiguration

@Configuration
public class EurekaServerInitializerConfiguration
        implements ServletContextAware, SmartLifecycle, Ordered {

    private static final Log log = LogFactory.getLog(EurekaServerInitializerConfiguration.class);

    @Autowired
    private EurekaServerConfig eurekaServerConfig;

    private ServletContext servletContext;

    @Autowired
    private ApplicationContext applicationContext;

    @Autowired
    private EurekaServerBootstrap eurekaServerBootstrap;

    private boolean running;

    private int order = 1;

    @Override
    public void setServletContext(ServletContext servletContext) {
        this.servletContext = servletContext;
    }

    @Override
    public void start() {
        new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    //TODO: is this class even needed now?
                    eurekaServerBootstrap.contextInitialized(EurekaServerInitializerConfiguration.this.servletContext);
                    log.info("Started Eureka Server");

                    publish(new EurekaRegistryAvailableEvent(getEurekaServerConfig()));
                    EurekaServerInitializerConfiguration.this.running = true;
                    publish(new EurekaServerStartedEvent(getEurekaServerConfig()));
                }
                catch (Exception ex) {
                    // Help!
                    log.error("Could not initialize Eureka servlet context", ex);
                }
            }
        }).start();
    }

可以看到EurekaServerInitializerConfiguration实现了SmartLifecycle，也就意味着Spring容器启动时
会去执行start()方法。加载所有的EurekaServer的配置

EurekaServerAutoConfiguration

实例化了EurekaServer的管控台的Controller类 EurekaController

 实例化EurekaServerBootstrap类

 实例化jersey相关配置类

jerseyApplication 方法，在容器中存放了一个jerseyApplication对象，jerseyApplication()方法里的
东西和Spring源码里扫描@Component逻辑类似，扫描@Path和@Provider标签，然后封装成
beandefinition，封装到Application的set容器里。通过filter过滤器来过滤url进行映射到对象的Controller

暴露的服务端接口
由于集成了Jersey，我们可以找到在EurekaServer的依赖包中的 eureka-core-1.9.8.jar ,可以看到一些列的XXXResource

 这些类都是通过Jersey发布的供客户端调用的服务接口。

服务端接受客户端的注册
在ApplicationResource.addInstance()方法中可以看到 this.registry.register(info,"true".equals(isReplication));

 继续找到父类的register方法可以看到整个注册的过程

public void register(InstanceInfo registrant, int leaseDuration, boolean isReplication) {
        try {
            read.lock();
            Map<String, Lease<InstanceInfo>> gMap = registry.get(registrant.getAppName());
            REGISTER.increment(isReplication);
            if (gMap == null) {
                final ConcurrentHashMap<String, Lease<InstanceInfo>> gNewMap = new ConcurrentHashMap<String, Lease<InstanceInfo>>();
                gMap = registry.putIfAbsent(registrant.getAppName(), gNewMap);
                if (gMap == null) {
                    gMap = gNewMap;
                }
            }
            Lease<InstanceInfo> existingLease = gMap.get(registrant.getId());
            // Retain the last dirty timestamp without overwriting it, if there is already a lease
            if (existingLease != null && (existingLease.getHolder() != null)) {
                Long existingLastDirtyTimestamp = existingLease.getHolder().getLastDirtyTimestamp();
                Long registrationLastDirtyTimestamp = registrant.getLastDirtyTimestamp();
                logger.debug("Existing lease found (existing={}, provided={}", existingLastDirtyTimestamp, registrationLastDirtyTimestamp);

                // this is a > instead of a >= because if the timestamps are equal, we still take the remote transmitted
                // InstanceInfo instead of the server local copy.
                if (existingLastDirtyTimestamp > registrationLastDirtyTimestamp) {
                    logger.warn("There is an existing lease and the existing lease's dirty timestamp {} is greater" +
                            " than the one that is being registered {}", existingLastDirtyTimestamp, registrationLastDirtyTimestamp);
                    logger.warn("Using the existing instanceInfo instead of the new instanceInfo as the registrant");
                    registrant = existingLease.getHolder();
                }
            } else {
                // The lease does not exist and hence it is a new registration
                synchronized (lock) {
                    if (this.expectedNumberOfClientsSendingRenews > 0) {
                        // Since the client wants to register it, increase the number of clients sending renews
                        this.expectedNumberOfClientsSendingRenews = this.expectedNumberOfClientsSendingRenews + 1;
                        updateRenewsPerMinThreshold();
                    }
                }
                logger.debug("No previous lease information found; it is new registration");
            }
            Lease<InstanceInfo> lease = new Lease<InstanceInfo>(registrant, leaseDuration);
            if (existingLease != null) {
                lease.setServiceUpTimestamp(existingLease.getServiceUpTimestamp());
            }
            gMap.put(registrant.getId(), lease);
            synchronized (recentRegisteredQueue) {
                recentRegisteredQueue.add(new Pair<Long, String>(
                        System.currentTimeMillis(),
                        registrant.getAppName() + "(" + registrant.getId() + ")"));
            }
            // This is where the initial state transfer of overridden status happens
            if (!InstanceStatus.UNKNOWN.equals(registrant.getOverriddenStatus())) {
                logger.debug("Found overridden status {} for instance {}. Checking to see if needs to be add to the "
                                + "overrides", registrant.getOverriddenStatus(), registrant.getId());
                if (!overriddenInstanceStatusMap.containsKey(registrant.getId())) {
                    logger.info("Not found overridden id {} and hence adding it", registrant.getId());
                    overriddenInstanceStatusMap.put(registrant.getId(), registrant.getOverriddenStatus());
                }
            }
            InstanceStatus overriddenStatusFromMap = overriddenInstanceStatusMap.get(registrant.getId());
            if (overriddenStatusFromMap != null) {
                logger.info("Storing overridden status {} from map", overriddenStatusFromMap);
                registrant.setOverriddenStatus(overriddenStatusFromMap);
            }

            // Set the status based on the overridden status rules
            InstanceStatus overriddenInstanceStatus = getOverriddenInstanceStatus(registrant, existingLease, isReplication);
            registrant.setStatusWithoutDirty(overriddenInstanceStatus);

            // If the lease is registered with UP status, set lease service up timestamp
            if (InstanceStatus.UP.equals(registrant.getStatus())) {
                lease.serviceUp();
            }
            registrant.setActionType(ActionType.ADDED);
            recentlyChangedQueue.add(new RecentlyChangedItem(lease));
            registrant.setLastUpdatedTimestamp();
            invalidateCache(registrant.getAppName(), registrant.getVIPAddress(), registrant.getSecureVipAddress());
            logger.info("Registered instance {}/{} with status {} (replication={})",
                    registrant.getAppName(), registrant.getId(), registrant.getStatus(), isReplication);
        } finally {
            read.unlock();
        }
    }

服务端接受客户端的续约
在InstanceResource的renewLease方法中完成客户端的心跳（续约）处理，其中最关键的方法就是
this.registry.renew(this.app.getName(), this.id, isFromReplicaNode)

public boolean renew(String appName, String id, boolean isReplication) {
        RENEW.increment(isReplication);
        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());
                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);

                }
            }
            renewsLastMin.increment();
            leaseToRenew.renew();
            return true;
        }
    }

服务剔除
在AbstractInstanceRegistry.postInit()方法，在此方法里开启了一个每60秒调用一次
EvictionTask.evict()的定时器。

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<>();
        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.
        int registrySize = (int) getLocalRegistrySize();
        int registrySizeThreshold = (int) (registrySize * serverConfig.getRenewalPercentThreshold());
        int evictionLimit = registrySize - registrySizeThreshold;

        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);
                internalCancel(appName, id, false);
            }
        }
    }

自动装载

在服务消费者导入的坐标中有 spring-cloud-netflix-eureka-client-2.1.0.RELEASE.jar 找到其中
的 spring.factories 可以看到所有自动装载的配置类

 服务注册，心跳续约等，感兴趣的可以自己看一下

在renew()这个方法中,首先向注册中心执行了心跳续约的请求,StatusCode为200成功,若为404则执行
register()重新注册操作;
最后总结一下eureka客户端做的事情;
1.根据配置文件初始化bean,创建客户端实例信息 InstanceInfo
2.第一次全量拉取注册中心服务列表(url=/apps),初始化周期任务:
2.1 CacheRefreshThread 定时刷新本地缓存服务列表,若是客户端第一次拉取,则会全量拉取,后面
则增量拉取.若增量拉取失败则全量拉取,配置属性为eureka.client.registryFetchIntervalSeconds=30默
认拉取一次;
2.2 HeartbeatThread 通过renew()续约任务,维持于注册中心的心跳(url=/apps/ {id}),若
返回状态码为404则说明该服务实例没有在注册中心注册,执行register()向注册中心注册实例信息;
2.3 ApplicationInfoManager.StatusChangeListener 注册实例状态监听类,监听服务实例状态变化,
向注册中心同步实例状态;
2.4 InstanceInfoReplicator 定时刷新实例状态,并向注册中心同步,默认
eureka.client.instanceInfoReplicationIntervalSeconds=30执行一次.若实例状态有变更,则重新执行注册