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
来源：https://www.cnblogs.com/dalianpai/p/12263438.html