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这篇文章给大家介绍怎么在SpringCloud中实现Eureka注册，内容非常详细，感兴趣的小伙伴们可以参考借鉴，希望对大家能有所帮助。
一、Eureka的服务端
eureka的服务端核心类是EurekaBootstrap，该类实现了一个ServletContextListener的监听器。因此我们可以断定eureka是基于servlet容器实现的。关键代码如下：
public class EurekaBootStrap implements ServletContextListener {
//...省略相关代码
/**
* Initializes Eureka, including syncing up with other Eureka peers and publishing the registry.
*
* @see
* javax.servlet.ServletContextListener#contextInitialized(javax.servlet.ServletContextEvent)
*/
@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);
}
}
//省略相关代码.....
}我们可以看到在ServletContext初始化完成时，会初始化Eureka环境，然后初始化EurekaServerContext，那么我们在看一看initEurekaServerContext方法：
/**
* init hook for server context. Override for custom logic.
*/
protected void initEurekaServerContext() throws Exception {
// .....
ApplicationInfoManager applicationInfoManager = null;
if (eurekaClient == null) {
EurekaInstanceConfig instanceConfig = isCloud(ConfigurationManager.getDeploymentContext())
? new CloudInstanceConfig()
: new MyDataCenterInstanceConfig();
applicationInfoManager = new ApplicationInfoManager(
instanceConfig, new EurekaConfigBasedInstanceInfoProvider(instanceConfig).get());
EurekaClientConfig eurekaClientConfig = new DefaultEurekaClientConfig();
eurekaClient = new DiscoveryClient(applicationInfoManager, eurekaClientConfig);
} else {
applicationInfoManager = eurekaClient.getApplicationInfoManager();
}
PeerAwareInstanceRegistry registry;
if (isAws(applicationInfoManager.getInfo())) {
registry = new AwsInstanceRegistry(
eurekaServerConfig,
eurekaClient.getEurekaClientConfig(),
serverCodecs,
eurekaClient
);
awsBinder = new AwsBinderDelegate(eurekaServerConfig, eurekaClient.getEurekaClientConfig(), registry, applicationInfoManager);
awsBinder.start();
} else {
registry = new PeerAwareInstanceRegistryImpl(
eurekaServerConfig,
eurekaClient.getEurekaClientConfig(),
serverCodecs,
eurekaClient
);
}
//....省略部分代码
}在这个方法里会创建许多与eureka服务相关的对象，在这里我列举了两个核心对象分别是eurekaClient与PeerAwareInstanceRegistry，关于客户端部分我们等会再说，我们现在来看看PeerAwareInstanceRegistry到底是做什么用的，这里我写贴出关于这个类的类图：
根据类图我们可以清晰的发现PeerAwareInstanceRegistry的最顶层接口为LeaseManager与LookupService,其中LookupService定义了最基本的发现示例的行为而LeaseManager定义了处理客户端注册，续约，注销等操作。那么在这篇文章我们还是重点关注一下LeaseManager的相关接口的实现。回过头来我们在看PeerAwareInstanceRegistry，其实这个类用于多个节点下复制相关信息，比如说一个节点注册续约与下线那么通过这个类将会相关复制(通知)到各个节点。我们来看看它是怎么处理客户端注册的：
/**
* Registers the information about the {@link InstanceInfo} and replicates
* this information to all peer eureka nodes. If this is replication event
* from other replica nodes then it is not replicated.
*
* @param info
* the {@link InstanceInfo} to be registered and replicated.
* @param isReplication
* true if this is a replication event from other replica nodes,
* false otherwise.
*/
@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);
}我们可以看到它调用了父类的register方法后又通过replicateToPeers复制对应的行为到其他节点，具体如何复制的先不在这里讨论，我们重点来看看注册方法，我们在父类里找到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 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.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>(registrant, leaseDuration);
if (existingLease != null) {
lease.setServiceUpTimestamp(existingLease.getServiceUpTimestamp());
}
gMap.put(registrant.getId(), lease);
//。。。省略部分代码
}通过源代码，我们来简要梳理一下流程：
1）首先根据appName获取一些列的服务实例对象，如果为Null,则新创建一个map并把当前的注册应用程序信息添加到此Map当中，这里有一个Lease对象，这个类描述了泛型T的时间属性，比如说注册时间，服务启动时间，最后更新时间等，大家可以关注一下它的实现：
/*
* Copyright 2012 Netflix, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.netflix.eureka.lease;
import com.netflix.eureka.registry.AbstractInstanceRegistry;
/**
* Describes a time-based availability of a {@link T}. Purpose is to avoid
* accumulation of instances in {@link AbstractInstanceRegistry} as result of ungraceful
* shutdowns that is not uncommon in AWS environments.
*
* If a lease elapses without renewals, it will eventually expire consequently
* marking the associated {@link T} for immediate eviction - this is similar to
* an explicit cancellation except that there is no communication between the
* {@link T} and {@link LeaseManager}.
*
* @author Karthik Ranganathan, Greg Kim
*/
public class Lease<T> {
enum Action {
Register, Cancel, Renew
};
public static final int DEFAULT_DURATION_IN_SECS = 90;
private T holder;
private long evictionTimestamp;
private long registrationTimestamp;
private long serviceUpTimestamp;
// Make it volatile so that the expiration task would see this quicker
private volatile long lastUpdateTimestamp;
private long duration;
public Lease(T r, int durationInSecs) {
holder = r;
registrationTimestamp = System.currentTimeMillis();
lastUpdateTimestamp = registrationTimestamp;
duration = (durationInSecs * 1000);
}
/**
* Renew the lease, use renewal duration if it was specified by the
* associated {@link T} during registration, otherwise default duration is
* {@link #DEFAULT_DURATION_IN_SECS}.
*/
public void renew() {
lastUpdateTimestamp = System.currentTimeMillis() + duration;
}
/**
* Cancels the lease by updating the eviction time.
*/
public void cancel() {
if (evictionTimestamp <= 0) {
evictionTimestamp = System.currentTimeMillis();
}
}
/**
* Mark the service as up. This will only take affect the first time called,
* subsequent calls will be ignored.
*/
public void serviceUp() {
if (serviceUpTimestamp == 0) {
serviceUpTimestamp = System.currentTimeMillis();
}
}
/**
* Set the leases service UP timestamp.
*/
public void setServiceUpTimestamp(long serviceUpTimestamp) {
this.serviceUpTimestamp = serviceUpTimestamp;
}
/**
* Checks if the lease of a given {@link com.netflix.appinfo.InstanceInfo} has expired or not.
*/
public boolean isExpired() {
return isExpired(0l);
}
/**
* Checks if the lease of a given {@link com.netflix.appinfo.InstanceInfo} has expired or not.
*
* Note that due to renew() doing the 'wrong" thing and setting lastUpdateTimestamp to +duration more than
* what it should be, the expiry will actually be 2 * duration. This is a minor bug and should only affect
* instances that ungracefully shutdown. Due to possible wide ranging impact to existing usage, this will
* not be fixed.
*
* @param additionalLeaseMs any additional lease time to add to the lease evaluation in ms.
*/
public boolean isExpired(long additionalLeaseMs) {
return (evictionTimestamp > 0 || System.currentTimeMillis() > (lastUpdateTimestamp + duration + additionalLeaseMs));
}
/**
* Gets the milliseconds since epoch when the lease was registered.
*
* @return the milliseconds since epoch when the lease was registered.
*/
public long getRegistrationTimestamp() {
return registrationTimestamp;
}
/**
* Gets the milliseconds since epoch when the lease was last renewed.
* Note that the value returned here is actually not the last lease renewal time but the renewal + duration.
*
* @return the milliseconds since epoch when the lease was last renewed.
*/
public long getLastRenewalTimestamp() {
return lastUpdateTimestamp;
}
/**
* Gets the milliseconds since epoch when the lease was evicted.
*
* @return the milliseconds since epoch when the lease was evicted.
*/
public long getEvictionTimestamp() {
return evictionTimestamp;
}
/**
* Gets the milliseconds since epoch when the service for the lease was marked as up.
*
* @return the milliseconds since epoch when the service for the lease was marked as up.
*/
public long getServiceUpTimestamp() {
return serviceUpTimestamp;
}
/**
* Returns the holder of the lease.
*/
public T getHolder() {
return holder;
}
}2）根据当前注册的ID，如果能在map中取到则做以下操作：
2.1）根据当前存在节点的触碰时间和注册节点的触碰时间比较，如果前者的时间晚于后者的时间，那么当前注册的实例就以已存在的实例为准
2.2）否则更新其每分钟期望的续约数量及其阈值
3）将当前的注册节点存到map当中，至此我们的注册过程基本告一段落了
二、eureka客户端
在服务端servletContext初始化完毕时，会创建DiscoveryClient。熟悉eureka的朋友，一定熟悉这两个属性：fetchRegistry与registerWithEureka。在springcloud中集成eureka独立模式运行时，如果这两个值不为false，那么启动会报错，为什么会报错呢？其实答案就在DiscoveryClient的构造函数中：
@Inject
DiscoveryClient(ApplicationInfoManager applicationInfoManager, EurekaClientConfig config, AbstractDiscoveryClientOptionalArgs args,
Provider<BackupRegistry> backupRegistryProvider) {
//....省略部分代码
if (!config.shouldRegisterWithEureka() && !config.shouldFetchRegistry()) {
logger.info("Client configured to neither register nor query for data.");
scheduler = null;
heartbeatExecutor = null;
cacheRefreshExecutor = null;
eurekaTransport = null;
instanceRegionChecker = new InstanceRegionChecker(new PropertyBasedAzToRegionMapper(config), clientConfig.getRegion());
// 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();
logger.info("Discovery Client initialized at timestamp {} with initial instances count: {}",
initTimestampMs, this.getApplications().size());
return; // no need to setup up an network tasks and we are done
}
try {
// default size of 2 - 1 each for heartbeat and cacheRefresh
scheduler = Executors.newScheduledThreadPool(2,
new ThreadFactoryBuilder()
.setNameFormat("DiscoveryClient-%d")
.setDaemon(true)
.build());
heartbeatExecutor = new ThreadPoolExecutor(
1, clientConfig.getHeartbeatExecutorThreadPoolSize(), 0, TimeUnit.SECONDS,
new SynchronousQueue<Runnable>(),
new ThreadFactoryBuilder()
.setNameFormat("DiscoveryClient-HeartbeatExecutor-%d")
.setDaemon(true)
.build()
); // use direct handoff
cacheRefreshExecutor = new ThreadPoolExecutor(
1, clientConfig.getCacheRefreshExecutorThreadPoolSize(), 0, TimeUnit.SECONDS,
new SynchronousQueue<Runnable>(),
new ThreadFactoryBuilder()
.setNameFormat("DiscoveryClient-CacheRefreshExecutor-%d")
.setDaemon(true)
.build()
); // use direct handoff
eurekaTransport = new EurekaTransport();
scheduleServerEndpointTask(eurekaTransport, args);
//....省略部分代码
initScheduledTasks();
//....
}根据源代码，我们可以得出以下结论：
1）如果shouldRegisterWithEureka与shouldFetchRegistry都为false,那么直接return。
2）创建发送心跳与刷新缓存的线程池
3）初始化创建的定时任务
那么我们在看看initScheduledTasks()方法里有如下代码：
// Heartbeat timer scheduler.schedule( new TimedSupervisorTask( "heartbeat", scheduler, heartbeatExecutor, renewalIntervalInSecs, TimeUnit.SECONDS, expBackOffBound, new HeartbeatThread() ), renewalIntervalInSecs, TimeUnit.SECONDS);
此处是触发一个定时执行的线程，以秒为单位，根据renewalIntervalInSecs值定时执行发送心跳，HeartbeatThread线程执行如下：
/**
* The heartbeat task that renews the lease in the given intervals.
*/
private class HeartbeatThread implements Runnable {
public void run() {
if (renew()) {
lastSuccessfulHeartbeatTimestamp = System.currentTimeMillis();
}
}
}我们可以看到run方法里很简单执行renew方法，如果成功记录一下时间。renew方法：
/**
* 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("{} - Heartbeat status: {}", PREFIX + appPathIdentifier, httpResponse.getStatusCode());
if (httpResponse.getStatusCode() == 404) {
REREGISTER_COUNTER.increment();
logger.info("{} - Re-registering apps/{}", PREFIX + appPathIdentifier, instanceInfo.getAppName());
long timestamp = instanceInfo.setIsDirtyWithTime();
boolean success = register();
if (success) {
instanceInfo.unsetIsDirty(timestamp);
}
return success;
}
return httpResponse.getStatusCode() == 200;
} catch (Throwable e) {
logger.error("{} - was unable to send heartbeat!", PREFIX + appPathIdentifier, e);
return false;
}
}在这里发送心跳如果返回的是404，那么会执行注册操作，注意我们根据返回值httpResponse可以断定这一切的操作都是基于http请求的，到底是不是呢？我们继续看一下register方法：
/**
* 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;
}在这里又调用了eurekaTransport里registrationClient的方法：
private static final class EurekaTransport {
private ClosableResolver bootstrapResolver;
private TransportClientFactory transportClientFactory;
private EurekaHttpClient registrationClient;
private EurekaHttpClientFactory registrationClientFactory;
private EurekaHttpClient queryClient;
private EurekaHttpClientFactory queryClientFactory;
void shutdown() {
if (registrationClientFactory != null) {
registrationClientFactory.shutdown();
}
if (queryClientFactory != null) {
queryClientFactory.shutdown();
}
if (registrationClient != null) {
registrationClient.shutdown();
}
if (queryClient != null) {
queryClient.shutdown();
}
if (transportClientFactory != null) {
transportClientFactory.shutdown();
}
if (bootstrapResolver != null) {
bootstrapResolver.shutdown();
}
}
}在这里我们可以看到，eureka的客户端是使用http请求进行注册服务的，也就是说当我们创建DiscoveryClient就会向服务端进行实例的注册。
三、服务端提供的rest服务
服务端提供用于处理客户端注册请求的代码我们已经看过了，既然客户端是通过走HTTP协议进行注册的，那服务端总要有处理这个http请求的地址吧，其实eureka服务端是采用jax-rs标准提供rest方式进行暴露服务的，我们可以看一下这个类ApplicationResoure的addInstance方法:
/**
* Registers information about a particular instance for an
* {@link com.netflix.discovery.shared.Application}.
*
* @param info
* {@link InstanceInfo} information of the instance.
* @param isReplication
* a header parameter containing information whether this is
* replicated from other nodes.
*/
@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
}关于怎么在SpringCloud中实现Eureka注册就分享到这里了，希望以上内容可以对大家有一定的帮助，可以学到更多知识。如果觉得文章不错，可以把它分享出去让更多的人看到。
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