? 注册中心到底是什么？从学习微服务的时候就一直在想，又有什么作用？从开始的单机服务器，到多台服务器的协同调用。渐渐地明白了注册中心的重要性。
? 在小型项目中，用单台服务器完全可以满足需求；再大一点的项目，单台服务器可以通过扩展服务器的配置满足需求，直至到服务器的瓶颈；当超过了单台服务器的瓶颈后，可以使用多个服务器的请求来进行协同。
? 因为spring-cloud使用的是http请求来进行多服务器的协同合作，这里也只用http来进行说明。当我们通过http请求进行多个服务器来进行合作的时候，可能出现被请求的服务器宕机尔无响应，可能出现被请求的服务器服务器线程满了无法处理请求等，这时候就体现到了注册中心的重要性了。
? eureka作为注册中心之一，只是将将每台服务器的信息的存入到eureka-server中，通过eureka-client来连接eureka-server，其中所有的请求都是通过http来完成。当需要远程调用的时候，直接获取client中存放的需要调用的服务器地址，实现远程调用即可。
@EnableEurekaServer
//次注解只是向容器中注入一个Bean
//EurekaServerMarkerConfiguration类中的
@Bean
public EurekaServerMarkerConfiguration.Marker eurekaServerMarkerBean() {
return new EurekaServerMarkerConfiguration.Marker();
}
//在通过eureka-server的jar包中的spring.factory文件的配置
//org.springframework.boot.autoconfigure.EnableAutoConfiguration=//org.springframework.cloud.netflix.eureka.server.EurekaServerAutoConfiguration
//启动eureka服务器。
//EurekaServerAutoConfiguration中，
//配置了http的入口controlller
@Bean
@ConditionalOnProperty(
prefix = "eureka.dashboard",
name = {"enabled"},
matchIfMissing = true
)
public EurekaController eurekaController() {
return new EurekaController(this.applicationInfoManager);
}
//配置了实例注册器，内部维护的就是eureka-client的信息
@Bean
public PeerAwareInstanceRegistry peerAwareInstanceRegistry(ServerCodecs serverCodecs) {
this.eurekaClient.getApplications();
return new InstanceRegistry(this.eurekaServerConfig, this.eurekaClientConfig, serverCodecs, this.eurekaClient, this.instanceRegistryProperties.getExpectedNumberOfClientsSendingRenews(), this.instanceRegistryProperties.getDefaultOpenForTrafficCount());
}
//jersy应用，eureka-client可以通过http请求，修改eureka维护的注册信息。
//jersy也是一个web框架，专注于restFull，eureka作为注册中心将会使用到两个web框架
//一个webMvc提供dashboar，一个jersy提供了以http请求方式维护注册信息
@Bean
public Application jerseyApplication(Environment environment, ResourceLoader resourceLoader) {
ClassPathScanningCandidateComponentProvider provider = new ClassPathScanningCandidateComponentProvider(false, environment);
provider.addIncludeFilter(new AnnotationTypeFilter(Path.class));
provider.addIncludeFilter(new AnnotationTypeFilter(Provider.class));
Set<Class<?>> classes = new HashSet();
String[] var5 = EUREKA_PACKAGES;
int var6 = var5.length;
for(int var7 = 0; var7 < var6; ++var7) {
String basePackage = var5[var7];
Set<BeanDefinition> beans = provider.findCandidateComponents(basePackage);
Iterator var10 = beans.iterator();
while(var10.hasNext()) {
BeanDefinition bd = (BeanDefinition)var10.next();
Class<?> cls = ClassUtils.resolveClassName(bd.getBeanClassName(), resourceLoader.getClassLoader());
classes.add(cls);
}
}
Map<String, Object> propsAndFeatures = new HashMap();
propsAndFeatures.put("com.sun.jersey.config.property.WebPageContentRegex", "/eureka/(fonts|images|css|js)/.*");
DefaultResourceConfig rc = new DefaultResourceConfig(classes);
rc.setPropertiesAndFeatures(propsAndFeatures);
return rc;
}
//等等还有许多bean，暂不一一说明
? 我们通过访问dashboard面板是通过两个请求完成的，一种是EurekaController 提供的请求为“/”的资源，还有一个就是jersy提供的数据"eureka/status"的资源提供数据,返回dashboard面板页面。我们可以自己在EurekaController的资源和ApplicationResource的eureka/status中打断点，查看返回的结果来进行验证，不得不说设计的很漂亮，需要找半天。有兴趣的人可以自己看看jersy开了多少个web接口，自己请求看看分别有哪些东西。jersy的资源都在eureka-core的com.netflix.eureka.resources包中。
? 实例注册是jersy提供的一个比较重要的接口，在applicationResource中，为一个post请求，在这个其你去里面可以看见eureka-client传给服务器有哪些信息，通过这些信息，eureka可以提供哪些功能。
@POST
@Consumes({"application/json", "application/xml"})
public Response addInstance(InstanceInfo info, @HeaderParam("x-netflix-discovery-replication") String isReplication) {
logger.debug("Registering instance {} (replication={})", info.getId(), isReplication);
if (this.isBlank(info.getId())) {
return Response.status(400).entity("Missing instanceId").build();
} else if (this.isBlank(info.getHostName())) {
return Response.status(400).entity("Missing hostname").build();
} else if (this.isBlank(info.getIPAddr())) {
return Response.status(400).entity("Missing ip address").build();
} else if (this.isBlank(info.getAppName())) {
return Response.status(400).entity("Missing appName").build();
} else if (!this.appName.equals(info.getAppName())) {
return Response.status(400).entity("Mismatched appName, expecting " + this.appName + " but was " + info.getAppName()).build();
} else if (info.getDataCenterInfo() == null) {
return Response.status(400).entity("Missing dataCenterInfo").build();
} else if (info.getDataCenterInfo().getName() == null) {
return Response.status(400).entity("Missing dataCenterInfo Name").build();
} else {
DataCenterInfo dataCenterInfo = info.getDataCenterInfo();
if (dataCenterInfo instanceof UniqueIdentifier) {
String dataCenterInfoId = ((UniqueIdentifier)dataCenterInfo).getId();
if (this.isBlank(dataCenterInfoId)) {
boolean experimental = "true".equalsIgnoreCase(this.serverConfig.getExperimental("registration.validation.dataCenterInfoId"));
if (experimental) {
String entity = "DataCenterInfo of type " + dataCenterInfo.getClass() + " must contain a valid id";
return Response.status(400).entity(entity).build();
}
if (dataCenterInfo instanceof AmazonInfo) {
AmazonInfo amazonInfo = (AmazonInfo)dataCenterInfo;
String effectiveId = amazonInfo.get(MetaDataKey.instanceId);
if (effectiveId == null) {
amazonInfo.getMetadata().put(MetaDataKey.instanceId.getName(), info.getId());
}
} else {
logger.warn("Registering DataCenterInfo of type {} without an appropriate id", dataCenterInfo.getClass());
}
}
}
this.registry.register(info, "true".equals(isReplication));
return Response.status(204).build();
}
}
//abstractInstanceRegistry类中注册功能
public void register(InstanceInfo registrant, int leaseDuration, boolean isReplication) {
try {
this.read.lock();
Map<String, Lease<InstanceInfo>> gMap = (Map)this.registry.get(registrant.getAppName());
EurekaMonitors.REGISTER.increment(isReplication);
if (gMap == null) {
ConcurrentHashMap<String, Lease<InstanceInfo>> gNewMap = new ConcurrentHashMap();
gMap = (Map)this.registry.putIfAbsent(registrant.getAppName(), gNewMap);
if (gMap == null) {
gMap = gNewMap;
}
}
Lease<InstanceInfo> existingLease = (Lease)((Map)gMap).get(registrant.getId());
if (existingLease != null && existingLease.getHolder() != null) {
Long existingLastDirtyTimestamp = ((InstanceInfo)existingLease.getHolder()).getLastDirtyTimestamp();
Long registrationLastDirtyTimestamp = registrant.getLastDirtyTimestamp();
logger.debug("Existing lease found (existing={}, provided={}", existingLastDirtyTimestamp, registrationLastDirtyTimestamp);
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 = (InstanceInfo)existingLease.getHolder();
}
} else {
synchronized(this.lock) {
if (this.expectedNumberOfClientsSendingRenews > 0) {
++this.expectedNumberOfClientsSendingRenews;
this.updateRenewsPerMinThreshold();
}
}
logger.debug("No previous lease information found; it is new registration");
}
Lease<InstanceInfo> lease = new Lease(registrant, leaseDuration);
if (existingLease != null) {
lease.setServiceUpTimestamp(existingLease.getServiceUpTimestamp());
}
((Map)gMap).put(registrant.getId(), lease);
synchronized(this.recentRegisteredQueue) {
this.recentRegisteredQueue.add(new Pair(System.currentTimeMillis(), registrant.getAppName() + "(" + registrant.getId() + ")"));
}
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 (!this.overriddenInstanceStatusMap.containsKey(registrant.getId())) {
logger.info("Not found overridden id {} and hence adding it", registrant.getId());
this.overriddenInstanceStatusMap.put(registrant.getId(), registrant.getOverriddenStatus());
}
}
InstanceStatus overriddenStatusFromMap = (InstanceStatus)this.overriddenInstanceStatusMap.get(registrant.getId());
if (overriddenStatusFromMap != null) {
logger.info("Storing overridden status {} from map", overriddenStatusFromMap);
registrant.setOverriddenStatus(overriddenStatusFromMap);
}
InstanceStatus overriddenInstanceStatus = this.getOverriddenInstanceStatus(registrant, existingLease, isReplication);
registrant.setStatusWithoutDirty(overriddenInstanceStatus);
if (InstanceStatus.UP.equals(registrant.getStatus())) {
lease.serviceUp();
}
registrant.setActionType(ActionType.ADDED);
this.recentlyChangedQueue.add(new AbstractInstanceRegistry.RecentlyChangedItem(lease));
registrant.setLastUpdatedTimestamp();
this.invalidateCache(registrant.getAppName(), registrant.getVIPAddress(), registrant.getSecureVipAddress());
logger.info("Registered instance {}/{} with status {} (replication={})", new Object[]{registrant.getAppName(), registrant.getId(), registrant.getStatus(), isReplication});
} finally {
this.read.unlock();
}
}
? 这个里面实际就是维护了一个Map集合，通过http请求，将需要客户端的信息放入到Map中，如此简单。还记得开始学的时候，就有人说过eureka的界面很丑，git中曾有大佬自己做了个eureka页面。对比下nacos中的手动剔除实力等功能，想想只用提出一个map实例即可。
? eureka实例自动剔除，至于在那个类中定义的定时任务，一时上我也忘了。但是定时任务是30s调用一次这个方法，调用的方法在PeerAwareInstanceRegistryImpl类中的
public void openForTraffic(ApplicationInfoManager applicationInfoManager, int count) {
this.expectedNumberOfClientsSendingRenews = count;
this.updateRenewsPerMinThreshold();
logger.info("Got {} instances from neighboring DS node", count);
logger.info("Renew threshold is: {}", this.numberOfRenewsPerMinThreshold);
this.startupTime = System.currentTimeMillis();
if (count > 0) {
this.peerInstancesTransferEmptyOnStartup = false;
}
Name selfName = applicationInfoManager.getInfo().getDataCenterInfo().getName();
boolean isAws = Name.Amazon == selfName;
if (isAws && this.serverConfig.shouldPrimeAwsReplicaConnections()) {
logger.info("Priming AWS connections for all replicas..");
this.primeAwsReplicas(applicationInfoManager);
}
logger.info("Changing status to UP");
applicationInfoManager.setInstanceStatus(InstanceStatus.UP);
super.postInit();
}
学习使我快乐，希望对你也有所帮助，一起将这份快乐传递。原文：https://www.cnblogs.com/theStone/p/15024107.html