1.概述
要学会首先要使用：【SpringClould】SpringClould eureka 单机与集群搭建
Spring Cloud Eureka分为Server端和Client端，Server端作为应用的注册中心，Client端会向Server端注册自己的服务。
1.1 Eureka的一些概念
在Eureka的服务治理中，会涉及到下面一些概念：
服务注册：Eureka Client会通过发送REST请求的方式向Eureka Server注册自己的服务，提供自身的元数据，比如ip地址、端口、运行状况指标的url、主页地址等信息。Eureka Server接收到注册请求后，就会把这些元数据信息存储在一个双层的Map中。服务续约：在服务注册后，Eureka Client会维护一个心跳来持续通知Eureka Server，说明服务一直处于可用状态，防止被剔除。Eureka Client在默认的情况下会每隔30秒发送一次心跳来进行服务续约。服务同步：Eureka Server之间会互相进行注册，构建Eureka Server集群，不同Eureka Server之间会进行服务同步，用来保证服务信息的一致性。获取服务：服务消费者（Eureka Client）在启动的时候，会发送一个REST请求给Eureka Server，获取上面注册的服务清单，并且缓存在Eureka Client本地，默认缓存30秒。同时，为了性能考虑，Eureka Server也会维护一份只读的服务清单缓存，该缓存每隔30秒更新一次。服务调用：服务消费者在获取到服务清单后，就可以根据清单中的服务列表信息，查找到其他服务的地址，从而进行远程调用。Eureka有Region和Zone的概念，一个Region可以包含多个Zone，在进行服务调用时，优先访问处于同一个Zone中的服务提供者。服务下线：当Eureka Client需要关闭或重启时，就不希望在这个时间段内再有请求进来，所以，就需要提前先发送REST请求给Eureka Server，告诉Eureka Server自己要下线了，Eureka Server在收到请求后，就会把该服务状态置为下线（DOWN），并把该下线事件传播出去。服务剔除：有时候，服务实例可能会因为网络故障等原因导致不能提供服务，而此时该实例也没有发送请求给Eureka Server来进行服务下线，所以，还需要有服务剔除的机制。Eureka Server在启动的时候会创建一个定时任务，每隔一段时间（默认60秒），从当前服务清单中把超时没有续约（默认90秒）的服务剔除。自我保护：既然Eureka Server会定时剔除超时没有续约的服务，那就有可能出现一种场景，网络一段时间内发生了异常，所有的服务都没能够进行续约，Eureka Server就把所有的服务都剔除了，这样显然不太合理。所以，就有了自我保护机制，当短时间内，统计续约失败的比例，如果达到一定阈值，则会触发自我保护的机制，在该机制下，Eureka Server不会剔除任何的微服务，等到正常后，再退出自我保护机制。
从这些概念中，就可以知道大体的流程，Eureka Client向Eureka Server注册，并且维护心跳来进行续约，如果长时间不续约，就会被剔除。Eureka Server之间进行数据同步来形成集群，Eureka Client从Eureka Server获取服务列表，用来进行服务调用，Eureka Client服务重启前调用Eureka Server的接口进行下线操作。
2.源码分析
2.1 Eureka Server源码
我们在server端加入了注解后
@SpringBootApplication
@EnableEurekaServer
@EnableDiscoveryClient
public class EurekaServerNodeApplication {
public static void main(String[] args) {
System.out.println("xx");
SpringApplication.run(EurekaServerNodeApplication.class, args);
}
}
然后这个注解对应代码如下
import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import org.springframework.context.annotation.Import;
/**
* Annotation to activate Eureka Server related configuration {@link EurekaServerAutoConfiguration}
*
* @author Dave Syer
* @author Biju Kunjummen
*
*/
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Import(EurekaServerMarkerConfiguration.class)
public @interface EnableEurekaServer {
}
2.1.1 @EnableEurekaServer注解
@Configuration
public class EurekaServerMarkerConfiguration {
@Bean
public Marker eurekaServerMarkerBean() {
return new Marker();
}
class Marker {
}
}
spring-cloud-netflix-eureka-server.jar>spring.factories//spring boot会自动注入
内容
org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
org.springframework.cloud.netflix.eureka.server.EurekaServerAutoConfiguration
@Configuration
@Import({
EurekaServerInitializerConfiguration.class})
@ConditionalOnBean({
Marker.class})
@EnableConfigurationProperties({
EurekaDashboardProperties.class, InstanceRegistryProperties.class})
@PropertySource({
"classpath:/eureka/server.properties"})
public class EurekaServerAutoConfiguration extends WebMvcConfigurerAdapter {
//@Bean,向spring容器中注入一堆bean
}
2.1.2 EurekaServerInitializerConfiguration
EurekaServerInitializerConfiguration.start()
@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();
}
2.1.2.1 contextInitialized()
//初始化
public void contextInitialized(ServletContext context) {
try {
//初始化运行环境
this.initEurekaEnvironment();
//初始化eureka
this.initEurekaServerContext();
context.setAttribute(EurekaServerContext.class.getName(), this.serverContext);
} catch (Throwable var3) {
log.error("Cannot bootstrap eureka server :", var3);
throw new RuntimeException("Cannot bootstrap eureka server :", var3);
}
}
2.1.2.1.1 initEurekaEnvironment
protected void initEurekaEnvironment() throws Exception {
log.info("Setting the eureka configuration..");
String dataCenter = ConfigurationManager.getConfigInstance()
.getString(EUREKA_DATACENTER);
if (dataCenter == null) {
log.info(
"Eureka data center value eureka.datacenter is not set, defaulting to default");
ConfigurationManager.getConfigInstance()
.setProperty(ARCHAIUS_DEPLOYMENT_DATACENTER, DEFAULT);
}
else {
ConfigurationManager.getConfigInstance()
.setProperty(ARCHAIUS_DEPLOYMENT_DATACENTER, dataCenter);
}
String environment = ConfigurationManager.getConfigInstance()
.getString(EUREKA_ENVIRONMENT);
if (environment == null) {
ConfigurationManager.getConfigInstance()
.setProperty(ARCHAIUS_DEPLOYMENT_ENVIRONMENT, TEST);
log.info(
"Eureka environment value eureka.environment is not set, defaulting to test");
}
else {
ConfigurationManager.getConfigInstance()
.setProperty(ARCHAIUS_DEPLOYMENT_ENVIRONMENT, environment);
}
}
2.1.2.1.2 initEurekaServerContext
protected void initEurekaServerContext() throws Exception {
JsonXStream.getInstance().registerConverter(new V1AwareInstanceInfoConverter(), 10000);
XmlXStream.getInstance().registerConverter(new V1AwareInstanceInfoConverter(), 10000);
if (this.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");
//从其他eureka节点同步数据
int registryCount = this.registry.syncUp();
//剔除无效节点
this.registry.openForTraffic(this.applicationInfoManager, registryCount);
EurekaMonitors.registerAllStats();
}
2.1.2.1.2.1 registry.syncUp()
public int syncUp() {
// Copy entire entry from neighboring DS node
int count = 0;
//默认获取5次，前提条件是开启注册到eureka
//开启获取注册信息时，才会从其他节点获取
//registerWithEureka与fetchRegistry都要配置成true
for (int i = 0; ((i < serverConfig.getRegistrySyncRetries()) && (count == 0)); i++) {
if (i > 0) {
try {
Thread.sleep(serverConfig.getRegistrySyncRetryWaitMs());
} catch (InterruptedException e) {
logger.warn("Interrupted during registry transfer..");
break;
}
}
//获取注册表信息
Applications apps = eurekaClient.getApplications();
for (Application app : apps.getRegisteredApplications()) {
for (InstanceInfo instance : app.getInstances()) {
try {
if (isRegisterable(instance)) {
//将其他节点上的实例注册到当前服务中
register(instance, instance.getLeaseInfo().getDurationInSecs(), true);
count++;
}
} catch (Throwable t) {
logger.error("During DS init copy", t);
}
}
}
}
return count;
}
2.1.2.1.2.2 eurekaClient.getApplications()
@Inject
DiscoveryClient(ApplicationInfoManager applicationInfoManager, EurekaClientConfig config, AbstractDiscoveryClientOptionalArgs args,
Provider<BackupRegistry> backupRegistryProvider) {
...
try {
// default size of 2 - 1 each for heartbeat and cacheRefresh
//定时任务
//定时更新注册服务
//定时续约
scheduler = Executors.newScheduledThreadPool(2,
new ThreadFactoryBuilder()
.setNameFormat("DiscoveryClient-%d")
.setDaemon(true)
.build());
//续约任务
heartbeatExecutor = new ThreadPoolExecutor(
1, clientConfig.getHeartbeatExecutorThreadPoolSize(), 0, TimeUnit.SECONDS,
new SynchronousQueue<Runnable>(),
new ThreadFactoryBuilder()
.setNameFormat("DiscoveryClient-HeartbeatExecutor-%d")
.setDaemon(true)
.build()
); // use direct handoff
//更新注册表
cacheRefreshExecutor = new ThreadPoolExecutor(
1, clientConfig.getCacheRefreshExecutorThreadPoolSize(), 0, TimeUnit.SECONDS,
new SynchronousQueue<Runnable>(),
new ThreadFactoryBuilder()
.setNameFormat("DiscoveryClient-CacheRefreshExecutor-%d")
.setDaemon(true)
.build()
); // use direct handoff
...
} catch (Throwable e) {
throw new RuntimeException("Failed to initialize DiscoveryClient!", e);
}
//获取注册信息
if (clientConfig.shouldFetchRegistry() && !fetchRegistry(false)) {
fetchRegistryFromBackup();
}
...
// finally, init the schedule tasks (e.g. cluster resolvers, heartbeat, instanceInfo replicator, fetch
//初始化定时任务
initScheduledTasks();
try {
Monitors.registerObject(this);
} catch (Throwable e) {
logger.warn("Cannot register timers", e);
}
// This is a bit of hack to allow for existing code using DiscoveryManager.getInstance()
// to work with DI'd DiscoveryClient
DiscoveryManager.getInstance().setDiscoveryClient(this);
DiscoveryManager.getInstance().setEurekaClientConfig(config);
initTimestampMs = System.currentTimeMillis();
}
2.1.2.1.2.3 fetchRegistry方法
private boolean fetchRegistry(boolean forceFullRegistryFetch) {
Stopwatch tracer = FETCH_REGISTRY_TIMER.start();
try {
// If the delta is disabled or if it is the first time, get all
// applications
Applications applications = getApplications();
if (clientConfig.shouldDisableDelta()//是否禁用增量
|| (!Strings.isNullOrEmpty(clientConfig.getRegistryRefreshSingleVipAddress()))
|| forceFullRegistryFetch
|| (applications == null)//注册表为null
|| (applications.getRegisteredApplications().size() == 0)//注册表里的节点数据
|| (applications.getVersion() == -1)) //Client application does not have latest library supporting delta
{
//全量获取
getAndStoreFullRegistry();
} else {
//增量获取
getAndUpdateDelta(applications);
}
//更新hashcode
applications.setAppsHashCode(applications.getReconcileHashCode());
logTotalInstances();
} catch (Throwable e) {
return false;
} finally {
if (tracer != null) {
tracer.stop();
}
}
// Notify about cache refresh before updating the instance remote status
onCacheRefreshed();
// Update remote status based on refreshed data held in the cache
updateInstanceRemoteStatus();
// registry was fetched successfully, so return true
return true;
}
getAndStoreFullRegistry 全量获取（http请求获取）
private void getAndStoreFullRegistry() throws Throwable {
long currentUpdateGeneration = fetchRegistryGeneration.get();
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");
} else if (fetchRegistryGeneration.compareAndSet(currentUpdateGeneration, currentUpdateGeneration + 1)) {
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");
}
}
getAndUpdateDelta 增量获取（增量获取）
private void getAndUpdateDelta(Applications applications) throws Throwable {
long currentUpdateGeneration = fetchRegistryGeneration.get();
Applications delta = null;
//获取增量数据
EurekaHttpResponse<Applications> httpResponse = eurekaTransport.queryClient.getDelta(remoteRegionsRef.get());
if (httpResponse.getStatusCode() == Status.OK.getStatusCode()) {
delta = httpResponse.getEntity();
}
//如果增量数据没有，获取全量数据
if (delta == null) {
getAndStoreFullRegistry();
}
//cas修改更新次数
else if (fetchRegistryGeneration.compareAndSet(currentUpdateGeneration, currentUpdateGeneration + 1)) {
String reconcileHashCode = "";
//加锁
if (fetchRegistryUpdateLock.tryLock()) {
try {
//更新增量节点
updateDelta(delta);
//获取hashcode
reconcileHashCode = getReconcileHashCode(applications);
} finally {
//解锁
fetchRegistryUpdateLock.unlock();
}
} else {
logger.warn("Cannot acquire update lock, aborting getAndUpdateDelta");
}
// There is a diff in number of instances for some reason
//与服务端节点比较，判断节点是否相同，不相同，做全量更新
if (!reconcileHashCode.equals(delta.getAppsHashCode()) || clientConfig.shouldLogDeltaDiff()) {
reconcileAndLogDifference(delta, reconcileHashCode); // this makes a remoteCall
}
}
}
Jersey提供服务，获取所有服务
@GET
public Response getContainers(@PathParam("version") String version,
@HeaderParam(HEADER_ACCEPT) String acceptHeader,
@HeaderParam(HEADER_ACCEPT_ENCODING) String acceptEncoding,
@HeaderParam(EurekaAccept.HTTP_X_EUREKA_ACCEPT) String eurekaAccept,
@Context UriInfo uriInfo,
@Nullable @QueryParam("regions") String regionsStr) {
...
//获取key
Key cacheKey = new Key(Key.EntityType.Application,
ResponseCacheImpl.ALL_APPS,
keyType, CurrentRequestVersion.get(), EurekaAccept.fromString(eurekaAccept), regions
);
Response response;
if (acceptEncoding != null && acceptEncoding.contains(HEADER_GZIP_VALUE)) {
//获取数据responseCache.getGZIP(cacheKey)
response = Response.ok(responseCache.getGZIP(cacheKey))
.header(HEADER_CONTENT_ENCODING, HEADER_GZIP_VALUE)
.header(HEADER_CONTENT_TYPE, returnMediaType)
.build();
} else {
response = Response.ok(responseCache.get(cacheKey))
.build();
}
return response;
}
responseCache.getGZIP(cacheKey)
@GET
public Response getContainers(@PathParam("version") String version,
@HeaderParam(HEADER_ACCEPT) String acceptHeader,
@HeaderParam(HEADER_ACCEPT_ENCODING) String acceptEncoding,
@HeaderParam(EurekaAccept.HTTP_X_EUREKA_ACCEPT) String eurekaAccept,
@Context UriInfo uriInfo,
@Nullable @QueryParam("regions") String regionsStr) {
...
//获取key
Key cacheKey = new Key(Key.EntityType.Application,
ResponseCacheImpl.ALL_APPS,
keyType, CurrentRequestVersion.get(), EurekaAccept.fromString(eurekaAccept), regions
);
Response response;
if (acceptEncoding != null && acceptEncoding.contains(HEADER_GZIP_VALUE)) {
//获取数据responseCache.getGZIP(cacheKey)
response = Response.ok(responseCache.getGZIP(cacheKey))
.header(HEADER_CONTENT_ENCODING, HEADER_GZIP_VALUE)
.header(HEADER_CONTENT_TYPE, returnMediaType)
.build();
} else {
response = Response.ok(responseCache.get(cacheKey))
.build();
}
return response;
}
三级缓存定义
@GET
public Response getContainers(@PathParam("version") String version,
@HeaderParam(HEADER_ACCEPT) String acceptHeader,
@HeaderParam(HEADER_ACCEPT_ENCODING) String acceptEncoding,
@HeaderParam(EurekaAccept.HTTP_X_EUREKA_ACCEPT) String eurekaAccept,
@Context UriInfo uriInfo,
@Nullable @QueryParam("regions") String regionsStr) {
...
//获取key
Key cacheKey = new Key(Key.EntityType.Application,
ResponseCacheImpl.ALL_APPS,
keyType, CurrentRequestVersion.get(), EurekaAccept.fromString(eurekaAccept), regions
);
Response response;
if (acceptEncoding != null && acceptEncoding.contains(HEADER_GZIP_VALUE)) {
//获取数据responseCache.getGZIP(cacheKey)
response = Response.ok(responseCache.getGZIP(cacheKey))
.header(HEADER_CONTENT_ENCODING, HEADER_GZIP_VALUE)
.header(HEADER_CONTENT_TYPE, returnMediaType)
.build();
} else {
response = Response.ok(responseCache.get(cacheKey))
.build();
}
return response;
}
下面再看下Eureka Server方面的源码，主要代码都在com.netflix.eureka:eureka-core-xxx.jar包下。
先看下这个包下的EurekaBootStrap类，这个类实现了ServletContextListener接口，在 Servlet API 中有一个 ServletContextListener 接口，它能够监听 ServletContext 对象的生命周期，当Servlet 容器启动或终止Web 应用时，会触发ServletContextEvent 事件，该事件由ServletContextListener 来处理。在 ServletContextListener 接口中定义了处理ServletContextEvent 事件的两个方法：contextInitialized和contextDestroyed。
EurekaBootStrap类中实现了这两个方法，在容器初始化的时候，就会执行这个类中的方法。
@Override
public void contextInitialized(ServletContextEvent event) {
try {
initEurekaEnvironment();
initEurekaServerContext();
ServletContext sc = event.getServletContext();
sc.setAttribute(EurekaServerContext.class.getName(), serverContext);
} catch (Throwable e) {
logger.error("Cannot bootstrap eureka server :", e);
throw new RuntimeException("Cannot bootstrap eureka server :", e);
}
}
在contextInitialized中，会初始化EurekaEnvironment和EurekaServerContext，进入EurekaServerContext方法，可以看到，在方法中，新建了几个类，PeerAwareInstanceRegistryImpl和PeerEurekaNodes等。
Eureka Server会接收Eureka Client发送的REST请求，进行服务的注册，续约，下线等操作，这部分代码在com.netflix.eureka:eureka-core-xx.jar包的resources目录下。
在resources目录下有个ApplicationResource类，类中有个方法，addInstance，这个方法就是接收注册服务请求的，下面看下这个方法：
com.netflix.eureka.resources.ApplicationResource#addInstance
@POST
@Consumes({
"application/json", "application/xml"})
public Response addInstance(InstanceInfo info,
@HeaderParam(PeerEurekaNode.HEADER_REPLICATION) String isReplication) {
logger.debug("Registering instance {} (replication={})", info.getId(), isReplication);
// validate that the instanceinfo contains all the necessary required fields
if (isBlank(info.getId())) {
return Response.status(400).entity("Missing instanceId").build();
} else if (isBlank(info.getHostName())) {
return Response.status(400).entity("Missing hostname").build();
} else if (isBlank(info.getIPAddr())) {
return Response.status(400).entity("Missing ip address").build();
} else if (isBlank(info.getAppName())) {
return Response.status(400).entity("Missing appName").build();
} else if (!appName.equals(info.getAppName())) {
return Response.status(400).entity("Mismatched appName, expecting " + 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();
}
// handle cases where clients may be registering with bad DataCenterInfo with missing data
DataCenterInfo dataCenterInfo = info.getDataCenterInfo();
if (dataCenterInfo instanceof UniqueIdentifier) {
String dataCenterInfoId = ((UniqueIdentifier) dataCenterInfo).getId();
if (isBlank(dataCenterInfoId)) {
boolean experimental = "true".equalsIgnoreCase(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();
} else if (dataCenterInfo instanceof AmazonInfo) {
AmazonInfo amazonInfo = (AmazonInfo) dataCenterInfo;
String effectiveId = amazonInfo.get(AmazonInfo.MetaDataKey.instanceId);
if (effectiveId == null) {
amazonInfo.getMetadata().put(AmazonInfo.MetaDataKey.instanceId.getName(), info.getId());
}
} else {
logger.warn("Registering DataCenterInfo of type {} without an appropriate id", dataCenterInfo.getClass());
}
}
}
registry.register(info, "true".equals(isReplication));
return Response.status(204).build(); // 204 to be backwards compatible
}
这个方法接收一个InstanceInfo info参数，这个参数就是要注册的Eureka Client节点的信息，在对这个InstanceInfo信息进行了一连串的校验之后，会调用registry.register(info, “true”.equals(isReplication))这个方法，进行服务注册，再进入这个方法看下：
@Override
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();
}
super.register(info, leaseDuration, isReplication);
replicateToPeers(Action.Register, info.getAppName(), info.getId(), info, null, isReplication);
}
这个方法就是在EurekaBootStrap中初始化的PeerAwareInstanceRegistryImpl类中的方法，在方法中，会获取InstanceInfo的续约时间信息，默认是90秒。然后调用父类的register方法注册，注册完后，会调用replicateToPeers方法，把这个节点的注册信息告诉其它Eureka Server节点。
先看下父类的register方法：
/**
* Registers a new instance with a given duration.
*
* @see com.netflix.eureka.lease.LeaseManager#register(java.lang.Object, int, boolean)
*/
public void register(InstanceInfo r, int leaseDuration, boolean isReplication) {
try {
read.lock();
Map<String, Lease<InstanceInfo>> gMap = registry.get(r.getAppName());
REGISTER.increment(isReplication);
if (gMap == null) {
final ConcurrentHashMap<String, Lease<InstanceInfo>> gNewMap =
new ConcurrentHashMap<String, Lease<InstanceInfo>>();
gMap = registry.putIfAbsent(r.getAppName(), gNewMap);
if (gMap == null) {
gMap = gNewMap;
}
}
Lease<InstanceInfo> existingLease = gMap.get(r.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 = r.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);
r.setLastDirtyTimestamp(existingLastDirtyTimestamp);
}
} else {
// The lease does not exist and hence it is a new registration
synchronized (lock) {
if (this.expectedNumberOfRenewsPerMin > 0) {
// Since the client wants to cancel it, reduce the threshold
// (1
// for 30 seconds, 2 for a minute)
this.expectedNumberOfRenewsPerMin = this.expectedNumberOfRenewsPerMin + 2;
this.numberOfRenewsPerMinThreshold =
(int) (this.expectedNumberOfRenewsPerMin * serverConfig.getRenewalPercentThreshold());
}
}
logger.debug("No previous lease information found; it is new registration");
}
Lease<InstanceInfo> lease = new Lease<InstanceInfo>(r, leaseDuration);
if (existingLease != null) {
lease.setServiceUpTimestamp(existingLease.getServiceUpTimestamp());
}
gMap.put(r.getId(), lease);
synchronized (recentRegisteredQueue) {
recentRegisteredQueue.add(new Pair<Long, String>(
System.currentTimeMillis(),
r.getAppName() + "(" + r.getId() + ")"));
}
// This is where the initial state transfer of overridden status happens
if (!InstanceStatus.UNKNOWN.equals(r.getOverriddenStatus())) {
logger.debug("Found overridden status {} for instance {}. Checking to see if needs to be add to the "
+ "overrides", r.getOverriddenStatus(), r.getId());
if (!overriddenInstanceStatusMap.containsKey(r.getId())) {
logger.info("Not found overridden id {} and hence adding it", r.getId());
overriddenInstanceStatusMap.put(r.getId(), r.getOverriddenStatus());
}
}
InstanceStatus overriddenStatusFromMap = overriddenInstanceStatusMap.get(r.getId());
if (overriddenStatusFromMap != null) {
logger.info("Storing overridden status {} from map", overriddenStatusFromMap);
r.setOverriddenStatus(overriddenStatusFromMap);
}
// Set the status based on the overridden status rules
InstanceStatus overriddenInstanceStatus = getOverriddenInstanceStatus(r, existingLease, isReplication);
r.setStatusWithoutDirty(overriddenInstanceStatus);
// If the lease is registered with UP status, set lease service up timestamp
if (InstanceStatus.UP.equals(r.getStatus())) {
lease.serviceUp();
}
r.setActionType(ActionType.ADDED);
recentlyChangedQueue.add(new RecentlyChangedItem(lease));
r.setLastUpdatedTimestamp();
invalidateCache(r.getAppName(), r.getVIPAddress(), r.getSecureVipAddress());
logger.info("Registered instance {}/{} with status {} (replication={})",
r.getAppName(), r.getId(), r.getStatus(), isReplication);
} finally {
read.unlock();
}
}
这个方法挺长的，有兴趣的可以仔细看下，方法功能大体还是注册信息了，注册的信息会存放在map中，而且还是个两层的ConcurrentHashMap<String, Map<String, Lease<InstanceInfo>>>，外层map的key是appName，也就是服务名，内层map的key是instanceId，也就是实例名。更新完map信息后，还会更新缓存信息。
注册完信息后，调用了replicateToPeers方法，向其他Eureka Server转发该注册信息，以便实现信息的同步。进到这个方法里面看下：
/**
* Replicates all eureka actions to peer eureka nodes except for replication
* traffic to this node.
*
*/
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.isThisMe(node.getServiceUrl())) {
continue;
}
replicateInstanceActionsToPeers(action, appName, id, info, newStatus, node);
}
} finally {
tracer.stop();
}
}
方法中会通过for循环遍历所有的PeerEurekaNode，调用replicateInstanceActionsToPeers方法，把信息复制给其他的Eureka Server节点，下面是replicateInstanceActionsToPeers方法：
/**
* Replicates all instance changes to peer eureka nodes except for
* replication traffic to this node.
*
*/
private void replicateInstanceActionsToPeers(Action action, String appName,
String id, InstanceInfo info, InstanceStatus newStatus,
PeerEurekaNode node) {
try {
InstanceInfo infoFromRegistry = null;
CurrentRequestVersion.set(Version.V2);
switch (action) {
case Cancel:
node.cancel(appName, id);
break;
case Heartbeat:
InstanceStatus overriddenStatus = overriddenInstanceStatusMap.get(id);
infoFromRegistry = getInstanceByAppAndId(appName, id, false);
node.heartbeat(appName, id, infoFromRegistry, overriddenStatus, false);
break;
case Register:
node.register(info);
break;
case StatusUpdate:
infoFromRegistry = getInstanceByAppAndId(appName, id, false);
node.statusUpdate(appName, id, newStatus, infoFromRegistry);
break;
case DeleteStatusOverride:
infoFromRegistry = getInstanceByAppAndId(appName, id, false);
node.deleteStatusOverride(appName, id, infoFromRegistry);
break;
}
} catch (Throwable t) {
logger.error("Cannot replicate information to {} for action {}", node.getServiceUrl(), action.name(), t);
}
}
方法中，会判断action具体的动作，如果是Register，就会调用node.register(info);
/**
* Sends the registration information of {@link InstanceInfo} receiving by
* this node to the peer node represented by this class.
*
* @param info
* the instance information {@link InstanceInfo} of any instance
* that is send to this instance.
* @throws Exception
*/
public void register(final InstanceInfo info) throws Exception {
long expiryTime = System.currentTimeMillis() + getLeaseRenewalOf(info);
batchingDispatcher.process(
taskId("register", info),
new InstanceReplicationTask(targetHost, Action.Register, info, null, true) {
public EurekaHttpResponse<Void> execute() {
return replicationClient.register(info);
}
},
expiryTime
);
}
在该方法中，是通过启动了一个任务，来向其它节点同步信息的，不是实时同步的。
2.2 Eureka Client源码
先从服务注册开始梳理，Eureka Client启动的时候就去Eureka Server注册服务。通过在启动类上添加@EnableDiscoveryClient这个注解，来声明这是一个Eureka Client。所以，先看下这个注解：
/**
* Annotation to enable a DiscoveryClient implementation.
* @author Spencer Gibb
*/
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@Import(EnableDiscoveryClientImportSelector.class)
public @interface EnableDiscoveryClient {
}
这个注解上方有注释，说这个注解是为了开启一个DiscoveryClient的实例。
接下来就可以搜索DiscoveryClient，可以发现有一个类，还有一个接口，查看这个类的关系图：
这个类实现了EurekaClient接口，而EurekaClient又继承了LookupService接口。这两个接口都是Netflix开源包中的内容，主要定义了针对Eureka发现服务的抽象方法。所以，DiscoveryClient类主要就是发现服务的。
接下来，就详细看下DiscoveryClient类，类上面的注释，说明了这个类是用来帮助和Eureka Server互相协作的，可以进行服务注册，服务续约，服务下线，获取服务列表。需要配置一个Eureka Server的Url列表。
上面提到的这个列表，就是我们在配置文件中配置的eureka.client.service-url.defaultZone这一选项，这个地址就是Eureka Server的地址，服务注册、服务续约以及其他的操作，都是向这个地址发送请求的。
在DiscoveryClient类中可以看到有很多方法，包括register()、renew()、shutdown()、unregister()等。
既然Eureka Client需要一开始先初始化DiscoveryClient实例，那就看下DiscoveryClient的构造方法。
DiscoveryClient的构造方法还是挺长的，里面初始化了一大堆的对象，不过可以观察到在new了这么一大堆对象之后，调用了initScheduledTasks();这个方法，所以，点进initScheduledTasks()方法里面看下。
@Inject
DiscoveryClient(ApplicationInfoManager applicationInfoManager, EurekaClientConfig config, AbstractDiscoveryClientOptionalArgs args,
Provider<BackupRegistry> backupRegistryProvider, EndpointRandomizer endpointRandomizer) {
。。。。。
// finally, init the schedule tasks (e.g. cluster resolvers, heartbeat, instanceInfo replicator, fetch
initScheduledTasks();
....
}
内容如下
在initScheduledTasks方法中，初始化了几个任务。
一开始有个if判断，判断是否需要从Eureka Server获取数据，如果为真，则初始化一个服务获取的定时任务。
还有有个if (clientConfig.shouldRegisterWithEureka())的判断，所以，当Eureka Client配置这个为true时，就会执行这个if语句里面的逻辑。if语句中，会初始化一个Heartbeat timer和InstanceInfoReplicator。Heartbeat timer就是不断的发送请求来维持心跳的，也就是服务续约的任务。而InstanceInfoReplicator类实现了Runnable接口，所以需要看下InstanceInfoReplicator类中的run方法。
public void run() {
try {
discoveryClient.refreshInstanceInfo();
Long dirtyTimestamp = instanceInfo.isDirtyWithTime();
if (dirtyTimestamp != null) {
discoveryClient.register();
instanceInfo.unsetIsDirty(dirtyTimestamp);
}
} catch (Throwable t) {
logger.warn("There was a problem with the instance info replicator", t);
} finally {
Future next = scheduler.schedule(this, replicationIntervalSeconds, TimeUnit.SECONDS);
scheduledPeriodicRef.set(next);
}
}
在run方法中，会调用我们之前看到的discoveryClient.register()方法进行服务注册。
/**
* Register with the eureka service by making the appropriate REST call.
*/
boolean register() throws Throwable {
logger.info(PREFIX + appPathIdentifier + ": registering service...");
EurekaHttpResponse<Void> httpResponse;
try {
httpResponse = eurekaTransport.registrationClient.register(instanceInfo);
} catch (Exception e) {
logger.warn("{} - registration failed {}", PREFIX + appPathIdentifier, e.getMessage(), e);
throw e;
}
if (logger.isInfoEnabled()) {
logger.info("{} - registration status: {}", PREFIX + appPathIdentifier, httpResponse.getStatusCode());
}
return httpResponse.getStatusCode() == 204;
}
register()方法，就会把instanceInfo信息，通过REST请求发送给Eureka Server。instanceInfo就是客服端服务的元数据。
所以，在initScheduledTasks方法中，做了三个操作，向Eureka Server注册服务，并且在条件满足的情况下，创建服务获取和服务续约两个定时任务。
我们在Eureka Client的配置文件中还配置了eureka.client.service-url.defaultZone这个地址，所以，在DiscoveryClient类中找一下serviceUrl这个关键字，可以看到有相应的方法：
/**
* @deprecated use {@link #getServiceUrlsFromConfig(String, boolean)} instead.
*/
@Deprecated
public static List<String> getEurekaServiceUrlsFromConfig(String instanceZone, boolean preferSameZone) {
return EndpointUtils.getServiceUrlsFromConfig(staticClientConfig, instanceZone, preferSameZone);
}
方法最终调用了EndpointUtils.getServiceUrlsFromConfig，点进这个方法看下：
/**
* Get the list of all eureka service urls from properties file for the eureka client to talk to.
*
* @param clientConfig the clientConfig to use
* @param instanceZone The zone in which the client resides
* @param preferSameZone true if we have to prefer the same zone as the client, false otherwise
* @return The list of all eureka service urls for the eureka client to talk to
*/
public static List<String> getServiceUrlsFromConfig(EurekaClientConfig clientConfig, String instanceZone, boolean preferSameZone) {
List<String> orderedUrls = new ArrayList<String>();
String region = getRegion(clientConfig);
String[] availZones = clientConfig.getAvailabilityZones(clientConfig.getRegion());
if (availZones == null || availZones.length == 0) {
availZones = new String[1];
availZones[0] = DEFAULT_ZONE;
}
logger.debug("The availability zone for the given region {} are {}", region, Arrays.toString(availZones));
int myZoneOffset = getZoneOffset(instanceZone, preferSameZone, availZones);
List<String> serviceUrls = clientConfig.getEurekaServerServiceUrls(availZones[myZoneOffset]);
if (serviceUrls != null) {
orderedUrls.addAll(serviceUrls);
}
int currentOffset = myZoneOffset == (availZones.length - 1) ? 0 : (myZoneOffset + 1);
while (currentOffset != myZoneOffset) {
serviceUrls = clientConfig.getEurekaServerServiceUrls(availZones[currentOffset]);
if (serviceUrls != null) {
orderedUrls.addAll(serviceUrls);
}
if (currentOffset == (availZones.length - 1)) {
currentOffset = 0;
} else {
currentOffset++;
}
}
if (orderedUrls.size() < 1) {
throw new IllegalArgumentException("DiscoveryClient: invalid serviceUrl specified!");
}
return orderedUrls;
}
在方法中，先获取了该项目配置的Region，又根据region获取了可用的zone列表。这里可以看到，项目的region只能属于一个，一个region下可以配置多个zone。
再通过getZoneOffset方法，从多个zone中选择对应的一个下标，根据这个zone来加载这个zone下的serviceUrls。
2.3 续约
DiscoveryClient的renew方法是服务续约，默认是30s一次
/**
* Renew with the eureka service by making the appropriate REST call
*/
boolean renew() {
EurekaHttpResponse<InstanceInfo> httpResponse;
try {
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();
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;
}
}
参考：https://blog.csdn.net/u010883443/article/details/108470758
https://segmentfault.com/a/1190000011668299