服务注册和发现之Eureka原理篇
概念
在传统应用组件间调用，通过接口规范约束来实现的，从而实现不同模块间良好协作；但是被拆分成微服务后，每个微服务实例的数量和网络地址都可能动态变化，使得原来硬编码的地址极不方便，故需要一个中心化的组件来进行服务的登记和管理。
服务注册中心：实现服务治理，管理所有的服务信息和状态。
注册中心好处：不用关心服务提供方数量、地址等细节。
注册中心技术栈：Eureka、Nacos、Consul、Zookeeper等。
服务注册与发现包括两部分：一个是服务器端，另一个是客户端
Server是一个公共服务，为Client提供服务注册和发现的功能，维护注册到自身的Client的相关信息，同时提供接口给Client获取注册表中其他服务的信息，使得动态变化的Client能够进行服务间的相互调用。
Client将自己的服务信息通过一定的方式登记到Server上，并在正常范围内维护自己信息一致性，方便其他服务发现自己，同时可以通过Server获取到自己依赖的其他服务信息，完成服务调用，还内置了负载均衡器，用来进行基本的负载均衡。
Spring Cloud以Eureka作为服务注册中心，是一个RESTful风格服务，是服务注册和发现的基础组件，它屏蔽了Server和Client的交互细节，使得开发者将精力放在业务上。
使用
Eureka单节点搭建
服务端
-
引入pom
<dependency> <groupId>org.springframework.cloud</groupId> <artifactId>spring-cloud-starter-netflix-eureka-server</artifactId> </dependency> -
application.yml
eureka: client: #是否将自己注册到Eureka Server,默认为true，由于当前就是server，故而设置成false，表明该服务不会向eureka注册自己的信息 register-with-eureka: false #是否从eureka server获取注册信息，由于单节点，不需要同步其他节点数据，用false fetch-registry: false #设置服务注册中心的URL，用于client和server端交流 service-url: defaultZone: http://username:pwd@localhost:7901/eureka/ -
代码
//启动类增加@EnableEurekaServer 标识该服务为注册中心服务端 @SpringBootApplication public class EurekaServerApplication { public static void main(String[] args) { SpringApplication.run(EurekaServerApplication.class, args); } }
客户端
-
引入pom
<dependency> <groupId>org.springframework.cloud</groupId> <artifactId>spring-cloud-starter-netflix-eureka-client</artifactId> </dependency> -
application.yml
#注册中心 eureka: client: #设置服务注册中心的URL service-url: defaultZone: http://username:pwd@localhost:7901/eureka/
Eureka也支持高可用，集群环境 搭建与单节点环境类似，需要注意客户端配置地址defaultZone时候，尽量写多个地址(写一个也行，EurekaServer注册表会自动同步，避免极端情况数据同步(Eureka是AP模型)不及时)
原理
注册中心本质：存储每个客户端的注册信息，EurekaClient从EurekaServer同步获取服务注册列表，通过一定的规则选择一个服务进行调用。Eureka架构图如下：
服务提供者：是一个Eureka client，向 Eureka Server注册和更细自己的信息，同时能从Eureka Server注册表中获取到其他服务的信息。
服务注册中心：提供服务注册和发现的功能。每个Eureka Client向Eureka Server注册自己的信息，也可以通过Eureka Server获取到其他服务的信息达到发现和调用其他服务的目的。
服务消费者：是一个Eureka client，通过Eureka Server获取注册的其他服务信息，从而找到所需要的服务发起远程调用。
注册：服务提供者向Eureka Server端注册自身的元数据以供服务发现。
续约：通过发送心跳到Server以维持和更新注册表中服务实例元数据的有效性。在一定时长内，Server没有收到Client的心跳信息，将默认下线，会把服务实例信息从注册表中删除。
下线：服务提供方在关闭时候主动向Server注销服务实例元数据，这时服务提供方实例数据将从Server的注册表中删除。
获取注册表：服务消费者Client向Server请求注册表信息，用于服务发现，从而发起远程调用。
源码
Eureka Client
Eureka Client工作流程
- Eureka Client通过SpringBoot自动装配，加载相关类，META-INF/spring.factories如下配置：
EurekaClientAutoConfiguration:Eureka client自动配置类，负责client中关键beans的配置和初始化
RibbonEurekaAutoConfiguration:Ribbon负载均衡相关配置
EurekaDiscoveryClientConfiguration:配置自动注册和应用的健康检查器
- Eureka 相关配置类
//EurekaClientConfigBean：封装了Eureka Client和Eureka Server交互所需要的配置信息
//EurekaInstanceConfigBean：封装了EurekaClient自身服务实例的配置信息，主要用于构建InstanceInfo
public void initComponent(EurekaInstanceConfig config) {
try {
this.config = config;
this.instanceInfo = new EurekaConfigBasedInstanceInfoProvider(config).get();
} catch (Throwable e) {
throw new RuntimeException("Failed to initialize ApplicationInfoManager", e);
}
}
-
Eureka客户端com.netflix.discovery.DiscoveryClient
该类是Eureka Client核心类 实现了EurekaClient接口(EurekaClient继承LookupService接口)，关键代码如下：
//构造方法
DiscoveryClient(ApplicationInfoManager applicationInfoManager,EurekaClientConfig config, AbstractDiscoveryClientOptionalArgs args,Provider<BackupRegistry> backupRegistryProvider, EndpointRandomizer endpointRandomizer) {
//初始化一些参数线程池等
...
//1.根据fetch-registry配置参数拉取注册表信息
if (clientConfig.shouldFetchRegistry() && !fetchRegistry(false)) {
fetchRegistryFromBackup();
}
//2.根据register-with-eureka配置参数向服务端注册
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);
}
}
//3.初始化定时任务 ①用于发送心跳 ②用于刷新缓存 ③按需注册事件向server注册
initScheduledTasks();
...
}
拉取注册表信息
private boolean fetchRegistry(boolean forceFullRegistryFetch) {
if (clientConfig.shouldDisableDelta()
|| (!Strings.isNullOrEmpty(clientConfig.getRegistryRefreshSingleVipAddress()))
|| forceFullRegistryFetch
|| (applications == null)
|| (applications.getRegisteredApplications().size() == 0)
|| (applications.getVersion() == -1))
{
...
//全量拉取
getAndStoreFullRegistry();
} else {
//增量拉取
getAndUpdateDelta(applications);
}
applications.setAppsHashCode(applications.getReconcileHashCode());
logTotalInstances();
...
}
//拉取方式有两种：全量和增量
//1.全量拉取
private void getAndStoreFullRegistry() throws Throwable {
long currentUpdateGeneration = fetchRegistryGeneration.get();
logger.info("Getting all instance registry info from the eureka server");
Applications apps = null;
EurekaHttpResponse<Applications> httpResponse = clientConfig.getRegistryRefreshSingleVipAddress() == null
? eurekaTransport.queryClient.getApplications(remoteRegionsRef.get())
: eurekaTransport.queryClient.getVip(clientConfig.getRegistryRefreshSingleVipAddress(), remoteRegionsRef.get());
if (httpResponse.getStatusCode() == Status.OK.getStatusCode()) {
apps = httpResponse.getEntity();
}
logger.info("The response status is {}", httpResponse.getStatusCode());
if (apps == null) {
logger.error("The application is null for some reason. Not storing this information");
//注意：AtomicLong cas进行版本管理
} else if (fetchRegistryGeneration.compareAndSet(currentUpdateGeneration, currentUpdateGeneration + 1)) {
//保留UP状态服务
localRegionApps.set(this.filterAndShuffle(apps));
logger.debug("Got full registry with apps hashcode {}", apps.getAppsHashCode());
} else {
logger.warn("Not updating applications as another thread is updating it already");
}
}
//2.增量拉取
private void getAndUpdateDelta(Applications applications) throws Throwable {
long currentUpdateGeneration = fetchRegistryGeneration.get();
Applications delta = null;
EurekaHttpResponse<Applications> httpResponse = eurekaTransport.queryClient.getDelta(remoteRegionsRef.get());
if (httpResponse.getStatusCode() == Status.OK.getStatusCode()) {
delta = httpResponse.getEntity();
}
if (delta == null) {
logger.warn("The server does not allow the delta revision to be applied because it is not safe. "
+ "Hence got the full registry.");
getAndStoreFullRegistry();
} else if (fetchRegistryGeneration.compareAndSet(currentUpdateGeneration, currentUpdateGeneration + 1)) {
logger.debug("Got delta update with apps hashcode {}", delta.getAppsHashCode());
String reconcileHashCode = "";
if (fetchRegistryUpdateLock.tryLock()) {
try {
updateDelta(delta);
reconcileHashCode = getReconcileHashCode(applications);
} finally {
fetchRegistryUpdateLock.unlock();
}
} else {
logger.warn("Cannot acquire update lock, aborting getAndUpdateDelta");
}
// There is a diff in number of instances for some reason
if (!reconcileHashCode.equals(delta.getAppsHashCode()) || clientConfig.shouldLogDeltaDiff()) {
reconcileAndLogDifference(delta, reconcileHashCode); // this makes a remoteCall
}
} else {
logger.warn("Not updating application delta as another thread is updating it already");
logger.debug("Ignoring delta update with apps hashcode {}, as another thread is updating it already", delta.getAppsHashCode());
}
}
服务注册
boolean register() throws Throwable {
logger.info(PREFIX + "{}: registering service...", appPathIdentifier);
EurekaHttpResponse<Void> httpResponse;
try {
//发送InstanceInfo信息到Server端
httpResponse = eurekaTransport.registrationClient.register(instanceInfo);
} catch (Exception e) {
logger.warn(PREFIX + "{} - registration failed {}", appPathIdentifier, e.getMessage(), e);
throw e;
}
if (logger.isInfoEnabled()) {
logger.info(PREFIX + "{} - registration status: {}", appPathIdentifier, httpResponse.getStatusCode());
}
return httpResponse.getStatusCode() == Status.NO_CONTENT.getStatusCode();
}
初始化三个定时任务
private void initScheduledTasks() {
//1.根据fetch-registry配置参数开启定时任务刷新client注册表缓存
if (clientConfig.shouldFetchRegistry()) {
// registry cache refresh timer
int registryFetchIntervalSeconds = clientConfig.getRegistryFetchIntervalSeconds();
int expBackOffBound = clientConfig.getCacheRefreshExecutorExponentialBackOffBound();
cacheRefreshTask = new TimedSupervisorTask(
"cacheRefresh",
scheduler,
cacheRefreshExecutor,
registryFetchIntervalSeconds,
TimeUnit.SECONDS,
expBackOffBound,
new CacheRefreshThread()
);
scheduler.schedule(
cacheRefreshTask,
registryFetchIntervalSeconds, TimeUnit.SECONDS);
}
//2.根据register-with-eureka配置参数开启心跳监测
if (clientConfig.shouldRegisterWithEureka()) {
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);
//3.1 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
// 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);
}
//3.2 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.start(clientConfig.getInitialInstanceInfoReplicationIntervalSeconds());
} else {
logger.info("Not registering with Eureka server per configuration");
}
}
续租
boolean renew() {
EurekaHttpResponse<InstanceInfo> httpResponse;
try {
//服务端发送心跳包
httpResponse = eurekaTransport.registrationClient.sendHeartBeat(instanceInfo.getAppName(), instanceInfo.getId(), instanceInfo, null);
logger.debug(PREFIX + "{} - Heartbeat status: {}", appPathIdentifier, httpResponse.getStatusCode());
if (httpResponse.getStatusCode() == Status.NOT_FOUND.getStatusCode()) {
REREGISTER_COUNTER.increment();
logger.info(PREFIX + "{} - Re-registering apps/{}", appPathIdentifier, instanceInfo.getAppName());
long timestamp = instanceInfo.setIsDirtyWithTime();
//若不存在 则发送注册
boolean success = register();
if (success) {
instanceInfo.unsetIsDirty(timestamp);
}
return success;
}
return httpResponse.getStatusCode() == Status.OK.getStatusCode();
} catch (Throwable e) {
logger.error(PREFIX + "{} - was unable to send heartbeat!", appPathIdentifier, e);
return false;
}
}
服务下线
@PreDestroy
@Override
public synchronized void shutdown() {
if (isShutdown.compareAndSet(false, true)) {
logger.info("Shutting down DiscoveryClient ...");
if (statusChangeListener != null && applicationInfoManager != null) {
applicationInfoManager.unregisterStatusChangeListener(statusChangeListener.getId());
}
//清除定时任务
cancelScheduledTasks();
//取消注册
// If APPINFO was registered
if (applicationInfoManager != null
&& clientConfig.shouldRegisterWithEureka()
&& clientConfig.shouldUnregisterOnShutdown()) {
applicationInfoManager.setInstanceStatus(InstanceStatus.DOWN);
unregister();
}
//关闭与服务端通讯连接
if (eurekaTransport != null) {
eurekaTransport.shutdown();
}
heartbeatStalenessMonitor.shutdown();
registryStalenessMonitor.shutdown();
Monitors.unregisterObject(this);
logger.info("Completed shut down of DiscoveryClient");
}
}
Eureka Server
Server主要有以下几个功能：接受服务注册、接受服务心跳、服务剔除、服务下线、集群同步、获取注册表中服务实例信息
Eureka Server同时也是一个Eureka Client，在不禁止Eureka Server的客户端行为时，它会向它配置文件中的其他Eureka Server进行拉取注册表、服务注册和发送心跳等操作。
- Eureka Server通过SpringBoot自动装配，加载相关类，META-INF/spring.factories如下配置：
EurekaServerAutoConfiguration:向spring的bean工厂添加eureka-server相关功能的bean
@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 {
}
EurekaServerAutoConfiguration生效条件 EurekaServerMarkerConfiguration.Marker所以服务端需要加上@EnableEurekaServer注解
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Import(EurekaServerMarkerConfiguration.class)
public @interface EnableEurekaServer {
}
- Eureka Server初始化类 EurekaServerInitializerConfiguration
public void start() {
new Thread(() -> {
try {
//初始化eureka的上下文环境
eurekaServerBootstrap.contextInitialized(
EurekaServerInitializerConfiguration.this.servletContext);
log.info("Started Eureka Server");
//发布服务端可注册事件通知
publish(new EurekaRegistryAvailableEvent(getEurekaServerConfig()));
EurekaServerInitializerConfiguration.this.running = true;
//发布Eureka Server已启动事件通知
publish(new EurekaServerStartedEvent(getEurekaServerConfig()));
}
catch (Exception ex) {
// Help!
log.error("Could not initialize Eureka servlet context", ex);
}
}).start();
}
EurekaServerBootstrap：启动类
public void contextInitialized(ServletContext context) {
try {
//初始化eureka环境
initEurekaEnvironment();
//初始化eureka context 其中两个主要功能如下
initEurekaServerContext();
context.setAttribute(EurekaServerContext.class.getName(), this.serverContext);
}
catch (Throwable e) {
log.error("Cannot bootstrap eureka server :", e);
throw new RuntimeException("Cannot bootstrap eureka server :", e);
}
}
protected void initEurekaServerContext() throws Exception {
// For backward compatibility
JsonXStream.getInstance().registerConverter(new V1AwareInstanceInfoConverter(),
XStream.PRIORITY_VERY_HIGH);
XmlXStream.getInstance().registerConverter(new V1AwareInstanceInfoConverter(),
XStream.PRIORITY_VERY_HIGH);
if (isAws(this.applicationInfoManager.getInfo())) {
this.awsBinder = new AwsBinderDelegate(this.eurekaServerConfig,
this.eurekaClientConfig, this.registry, this.applicationInfoManager);
this.awsBinder.start();
}
EurekaServerContextHolder.initialize(this.serverContext);
log.info("Initialized server context");
//从相邻的eureka节点复制注册表
int registryCount = this.registry.syncUp();
//与client 交换信息 其中包括 服务剔除定时任务开启 openForTraffic()>super.postInit()>EvictionTask
this.registry.openForTraffic(this.applicationInfoManager, registryCount);
// Register all monitoring statistics.
EurekaMonitors.registerAllStats();
}
- Server是围绕注册表管理的，有两个InstanceRegistry
com.netflix.eureka.registry.InstanceRegistry是euraka server中注册表管理的核心接口。职责是在内存中管理注册到Eureka Server中的服务实例信息。实现类有PeerAwareInstanceRegistryImpl。
org.springframework.cloud.netflix.eureka.server.InstanceRegistry对PeerAwareInstanceRegistryImpl进行了继承和扩展，使其适配Spring cloud的使用环境，主要的实现由PeerAwareInstanceRegistryImpl提供
com.netflix.eureka.registry.InstanceRegistry extends LeaseManager<InstanceInfo>, LookupService<String>
LookupService
LeaseManager
PeerAwareInstanceRegistryImpl关键代码如下：
- 服务注册
public void register(final InstanceInfo info, final boolean isReplication) {
int leaseDuration = Lease.DEFAULT_DURATION_IN_SECS;
if (info.getLeaseInfo() != null && info.getLeaseInfo().getDurationInSecs() > 0) {
leaseDuration = info.getLeaseInfo().getDurationInSecs();
}
//具体注册方法
super.register(info, leaseDuration, isReplication);
//注册完成后同步到它的peer节点
replicateToPeers(Action.Register, info.getAppName(), info.getId(), info, null, isReplication);
}
//super.register 注册核心逻辑
public void register(InstanceInfo registrant, int leaseDuration, boolean isReplication) {
try {
read.lock();
//构建注册信息 Map集合 从当前注册表查询 若不存在重新创建
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);
//修改数据保存到最近队列 用于客户端增量更新
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);
//修改数据保存到最近队列 用于客户端增量更新
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();
}
}
- 心跳续约
public boolean renew(final String appName, final String id, final boolean isReplication) {
//续约
if (super.renew(appName, id, isReplication)) {
//续约完成后同步到它的peer节点
replicateToPeers(Action.Heartbeat, appName, id, null, null, isReplication);
return true;
}
return false;
}
//super.renew() 续约核算逻辑
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();
//更新租期
leaseToRenew.renew();
return true;
}
}
//leaseToRenew.renew();
public void renew() {
lastUpdateTimestamp = System.currentTimeMillis() + duration;
}
- 服务下线
public boolean cancel(final String appName, final String id,
final boolean isReplication) {
//下线逻辑
if (super.cancel(appName, id, isReplication)) {
//下线完成后同步到它的peer节点
replicateToPeers(Action.Cancel, appName, id, null, null, isReplication);
return true;
}
return false;
}
public boolean cancel(String appName, String id, boolean isReplication) {
return internalCancel(appName, id, isReplication);
}
protected boolean internalCancel(String appName, String id, boolean isReplication) {
try {
read.lock();
CANCEL.increment(isReplication);
Map<String, Lease<InstanceInfo>> gMap = registry.get(appName);
Lease<InstanceInfo> leaseToCancel = null;
if (gMap != null) {
//从Map注册表中移除当前删除实例
leaseToCancel = gMap.remove(id);
}
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());
}
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 {
leaseToCancel.cancel();
InstanceInfo instanceInfo = leaseToCancel.getHolder();
String vip = null;
String svip = null;
if (instanceInfo != null) {
instanceInfo.setActionType(ActionType.DELETED);
recentlyChangedQueue.add(new RecentlyChangedItem(leaseToCancel));
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;
}
- 服务剔除
public void evict(long additionalLeaseMs) {
logger.debug("Running the evict task");
//自我保护策略判断 决定是否剔除服务 防止网络分区问题
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.
//遍历服务注册表获取租约到期服务列表
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.
//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 默认85%），得出要续租的数量
int registrySizeThreshold = (int) (registrySize * serverConfig.getRenewalPercentThreshold());
//理论要剔除的数量 = 总数-要续租的数量
int evictionLimit = registrySize - registrySizeThreshold;
//实际剔除的数量 = min(实际租期到期服务实例个数，理论剔除数量)
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);
internalCancel(appName, id, false);
}
}
}
//自我保护判断逻辑
public boolean isLeaseExpirationEnabled() {
//是否开通自我保护开关
if (!isSelfPreservationModeEnabled()) {
// The self preservation mode is disabled, hence allowing the instances to expire.
return true;
}
//续约数量 > 阀值 可以剔除
return numberOfRenewsPerMinThreshold > 0 && getNumOfRenewsInLastMin() > numberOfRenewsPerMinThreshold;
}
自我保护触发：
当每分钟心跳次数( renewsLastMin ) 小于 numberOfRenewsPerMinThreshold 时，并且开启自动保护模式开关( eureka.server.enable-self-preservation = true ) 时，触发自我保护机制，不再自动过期租约。
numberOfRenewsPerMinThreshold = expectedNumberOfRenewsPerMin * 续租百分比( eureka.server.renewalPercentThreshold, 默认0.85 )
expectedNumberOfRenewsPerMin = 当前注册的应用实例数 x 2
默认情况下，注册的应用实例每半分钟续租一次，那么一分钟心跳两次，因此 x 2 。
服务实例数：10个，期望每分钟续约数：10 * 2=20，期望阈值：20*0.85=17，自我保护少于17时 触发。
- 服务同步
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;
}
//具体同步方法
replicateInstanceActionsToPeers(action, appName, id, info, newStatus, node);
}
} finally {
tracer.stop();
}
}
-
Eureka事件
EurekaInstanceCanceledEvent 服务下线事件
EurekaInstanceRegisteredEvent 服务注册事件
EurekaInstanceRenewedEvent 服务续约事件
EurekaRegistryAvailableEvent 注册中心可用事件
EurekaServerStartedEvent 注册中心启动
注意：由于集群间的同步复制是通过HTTP的方式进行，基于网络的不可靠性，集群中的Eureka Server间的注册表信息难免存在不同步的时间节点，不满足CAP中的C(数据一致性)。
