eureka客户端源码分析

约定不等于承诺〃 2023-07-12 08:58 14阅读 0赞

### eureka客户端可以完成的事情 ###

1.  eureka客户端可以获取其他客户端的信息，用于向其他客户端发送请求。
2.  eureka客户端可以把自己注册到注册中心，这样其他客户端就可以发现本客户端，直接来调用本客户端。

### 相关依赖 ###

首先要是springboot应用

<dependency>
                <groupId>org.springframework.cloud</groupId>
                <artifactId>spring-cloud-starter-eureka</artifactId>
            </dependency>

我这里使用的版本是Brixton.SR5,不同版本的实现逻辑可能不一样。

### 逻辑详解 ###

启动类上需要加@EnableDiscoveryClient注解，我们打开该注解开一下代码。

/**
     * Annotation to enable a DiscoveryClient implementation.
     * @author Spencer Gibb
     */
    @Target(ElementType.TYPE)
    @Retention(RetentionPolicy.RUNTIME)
    @Documented
    @Inherited
    @Import(EnableDiscoveryClientImportSelector.class)
    public @interface EnableDiscoveryClient {
    
    }

按注释的意思就可以知道，这里是去启用DiscoveryClient的实现类。这里如何去启动的？大概的思路是通过springboot的starter机制实现的，通过扫描特定的配置类EurekaClientAutoConfiguration，在该配置类中，生成了DiscoveryClient的bean。这里贴一小段代码。

@Bean(destroyMethod = "shutdown")
    		@ConditionalOnMissingBean(value = EurekaClient.class, search = SearchStrategy.CURRENT)
    		public EurekaClient eurekaClient(ApplicationInfoManager manager,
    				EurekaClientConfig config) {
    			return new CloudEurekaClient(manager, config, this.optionalArgs,
    					this.context);
    		}

其实CloudEurekaClient里面的代码很少，基本都是父类DiscoveryClient实现的，我们直接看父类的方法。  
最后是调用了如下构造方法，这里先贴一下构造方法的具体代码，不用去研究。

@Inject
        DiscoveryClient(ApplicationInfoManager applicationInfoManager, EurekaClientConfig config, DiscoveryClientOptionalArgs args,
                        Provider<BackupRegistry> backupRegistryProvider) {
            //健康校验的，跳过
            if (args != null) {
                this.healthCheckHandlerProvider = args.healthCheckHandlerProvider;
                this.healthCheckCallbackProvider = args.healthCheckCallbackProvider;
                this.eventListeners.addAll(args.getEventListeners());
            } else {
                this.healthCheckCallbackProvider = null;
                this.healthCheckHandlerProvider = null;
            }
            
            //这主要是获取本应用信息的
            this.applicationInfoManager = applicationInfoManager;
            InstanceInfo myInfo = applicationInfoManager.getInfo();
    
            clientConfig = config;
            staticClientConfig = clientConfig;
            transportConfig = config.getTransportConfig();
            instanceInfo = myInfo;
            if (myInfo != null) {
                appPathIdentifier = instanceInfo.getAppName() + "/" + instanceInfo.getId();
            } else {
                logger.warn("Setting instanceInfo to a passed in null value");
            }
    
            this.backupRegistryProvider = backupRegistryProvider;
    
            this.urlRandomizer = new EndpointUtils.InstanceInfoBasedUrlRandomizer(instanceInfo);
            localRegionApps.set(new Applications());
    
            fetchRegistryGeneration = new AtomicLong(0);
    
            remoteRegionsToFetch = new AtomicReference<String>(clientConfig.fetchRegistryForRemoteRegions());
            remoteRegionsRef = new AtomicReference<>(remoteRegionsToFetch.get() == null ? null : remoteRegionsToFetch.get().split(","));
    
            //一些监视器
            if (config.shouldFetchRegistry()) {
                this.registryStalenessMonitor = new ThresholdLevelsMetric(this, METRIC_REGISTRY_PREFIX + "lastUpdateSec_", new long[]{15L, 30L, 60L, 120L, 240L, 480L});
            } else {
                this.registryStalenessMonitor = ThresholdLevelsMetric.NO_OP_METRIC;
            }
    
            if (config.shouldRegisterWithEureka()) {
                this.heartbeatStalenessMonitor = new ThresholdLevelsMetric(this, METRIC_REGISTRATION_PREFIX + "lastHeartbeatSec_", new long[]{15L, 30L, 60L, 120L, 240L, 480L});
            } else {
                this.heartbeatStalenessMonitor = ThresholdLevelsMetric.NO_OP_METRIC;
            }
    
            //如果不需要注册到eureka，也不需要从eureka读取信息的话，直接返回。
            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
            }
    
            //这里初始化了一些线程池，主要是给下面的task用的，
            //heartbeatExecutor用于心跳,cacheRefreshExecutor用于重新获取信息
            try {
                scheduler = Executors.newScheduledThreadPool(3,
                        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);
    
                AzToRegionMapper azToRegionMapper;
                if (clientConfig.shouldUseDnsForFetchingServiceUrls()) {
                    azToRegionMapper = new DNSBasedAzToRegionMapper(clientConfig);
                } else {
                    azToRegionMapper = new PropertyBasedAzToRegionMapper(clientConfig);
                }
                if (null != remoteRegionsToFetch.get()) {
                    azToRegionMapper.setRegionsToFetch(remoteRegionsToFetch.get().split(","));
                }
                instanceRegionChecker = new InstanceRegionChecker(azToRegionMapper, clientConfig.getRegion());
            } catch (Throwable e) {
                throw new RuntimeException("Failed to initialize DiscoveryClient!", e);
            }
    
            if (clientConfig.shouldFetchRegistry() && !fetchRegistry(false)) {
                fetchRegistryFromBackup();
            }
    
            //重点，刷新缓存和心跳是在这个方法里面干的
            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();
            logger.info("Discovery Client initialized at timestamp {} with initial instances count: {}",
                    initTimestampMs, this.getApplications().size());
        }

主要逻辑在initScheduledTasks()里面，我们直接看这个里面的实现。

/**
         * Initializes all scheduled tasks.
         */
        private void initScheduledTasks() {
            //如果需要获取注册中心的信息，则执行里面的定时任务。
            if (clientConfig.shouldFetchRegistry()) {
                // registry cache refresh timer
                int registryFetchIntervalSeconds = clientConfig.getRegistryFetchIntervalSeconds();
                int expBackOffBound = clientConfig.getCacheRefreshExecutorExponentialBackOffBound();
                //定时去获取注册中心的信息，这里主要的逻辑是通过CacheRefreshThread去实现的
                scheduler.schedule(
                        new TimedSupervisorTask(
                                "cacheRefresh",
                                scheduler,
                                cacheRefreshExecutor,
                                registryFetchIntervalSeconds,
                                TimeUnit.SECONDS,
                                expBackOffBound,
                                new CacheRefreshThread()
                        ),
                        registryFetchIntervalSeconds, TimeUnit.SECONDS);
            }
                
            //如果需要把自身注册到注册中心的话，执行里面的逻辑
            if (clientConfig.shouldRegisterWithEureka()) {
                int renewalIntervalInSecs = instanceInfo.getLeaseInfo().getRenewalIntervalInSecs();
                int expBackOffBound = clientConfig.getHeartbeatExecutorExponentialBackOffBound();
                logger.info("Starting heartbeat executor: " + "renew interval is: " + renewalIntervalInSecs);
    
                //每隔一段时间，发送心跳信息到注册中心，具体的逻辑由HeartbeatThread线程实现。
                // Heartbeat timer
                scheduler.schedule(
                        new TimedSupervisorTask(
                                "heartbeat",
                                scheduler,
                                heartbeatExecutor,
                                renewalIntervalInSecs,
                                TimeUnit.SECONDS,
                                expBackOffBound,
                                new HeartbeatThread()
                        ),
                        renewalIntervalInSecs, TimeUnit.SECONDS);
    
                // 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);
                }
    
                //用于更新本地instanceinfo并将其复制到远程服务器的任务
                instanceInfoReplicator.start(clientConfig.getInitialInstanceInfoReplicationIntervalSeconds());
            } else {
                logger.info("Not registering with Eureka server per configuration");
            }
        }

这里一共有三个逻辑

1.  获取注册中心信息
2.  心跳
3.  更新本地信息并同步至远程

#### 更新本地信息并同步至远程 ####

这里看下InstanceInfoReplicator的run方法

public void run() {
            try {
                //刷新本地配置信息
                discoveryClient.refreshInstanceInfo();
    
                Long dirtyTimestamp = instanceInfo.isDirtyWithTime();
                //如果本地信息已经更新了且没有同步到远程，才有dirtyTimestamp时间
                if (dirtyTimestamp != null) {
                    //向远程注册
                    discoveryClient.register();
                    
                    //已经同步到远程过了，这里需要更新状态，表明下次不需要重新注册
                    instanceInfo.unsetIsDirty(dirtyTimestamp);
                }
            } catch (Throwable t) {
                logger.warn("There was a problem with the instance info replicator", t);
            } finally {
                //这里会继续轮询，发现本地信息更新了，就会同步到远程
                Future next = scheduler.schedule(this, replicationIntervalSeconds, TimeUnit.SECONDS);
                scheduledPeriodicRef.set(next);
            }
        }

我们再看下注册方法，注册方法也很简单，只是调用一下http请求，把自身信息告诉远程。

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;
        }

#### 获取注册中心的信息 ####

这里主要看一下CacheRefreshThread的run方法，最后调用了fetchRegistry方法

private boolean fetchRegistry(boolean forceFullRegistryFetch) {
            Stopwatch tracer = FETCH_REGISTRY_TIMER.start();
    
            try {
                //获取原来注册中心获取的信息
                Applications applications = getApplications();
    
                //新增的情况
                if (clientConfig.shouldDisableDelta()
                        || (!Strings.isNullOrEmpty(clientConfig.getRegistryRefreshSingleVipAddress()))
                        || forceFullRegistryFetch
                        || (applications == null)
                        || (applications.getRegisteredApplications().size() == 0)
                        || (applications.getVersion() == -1)) //Client application does not have latest library supporting delta
                {
                    logger.info("Disable delta property : {}", clientConfig.shouldDisableDelta());
                    logger.info("Single vip registry refresh property : {}", clientConfig.getRegistryRefreshSingleVipAddress());
                    logger.info("Force full registry fetch : {}", forceFullRegistryFetch);
                    logger.info("Application is null : {}", (applications == null));
                    logger.info("Registered Applications size is zero : {}",
                            (applications.getRegisteredApplications().size() == 0));
                    logger.info("Application version is -1: {}", (applications.getVersion() == -1));
                    getAndStoreFullRegistry();
                } else {
                    //更新的情况
                    getAndUpdateDelta(applications);
                }
                applications.setAppsHashCode(applications.getReconcileHashCode());
                logTotalInstances();
            } catch (Throwable e) {
                logger.error(PREFIX + appPathIdentifier + " - was unable to refresh its cache! status = " + e.getMessage(), 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;
        }

这里直接看一个更新的情况getAndUpdateDelta

private void getAndUpdateDelta(Applications applications) throws Throwable {
            long currentUpdateGeneration = fetchRegistryGeneration.get();
    
            Applications delta = null;
            //调用远程获取信息
            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 {
                        //调用该方法更新了注册信息。
                        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());
            }
        }

#### 心跳 ####

下面再看下心跳，主要看HeartbeatThread的run方法,最后调用了renew方法。

boolean renew() {
            EurekaHttpResponse<InstanceInfo> httpResponse;
            try {
                //发送http请求，instanceInfo为客户端信息。
                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());
                    return register();
                }
                return httpResponse.getStatusCode() == 200;
            } catch (Throwable e) {
                logger.error("{} - was unable to send heartbeat!", PREFIX + appPathIdentifier, e);
                return false;
            }
        }

### 注册信息 ###

这里贴一个Applications类的代码，该类用于保存注册中心返回的信息，具体信息内容可以自己打断点查看。  
里面保存了很多数据结构，主要是为了后期数据更方便的使用。

/**
     * The class that wraps all the registry information returned by eureka server.
     *
     */
    @Serializer("com.netflix.discovery.converters.EntityBodyConverter")
    @XStreamAlias("applications")
    @JsonRootName("applications")
    public class Applications {
        private static final String APP_INSTANCEID_DELIMITER = "$$";
        private static final Logger logger = LoggerFactory.getLogger(Applications.class);
        private static final String STATUS_DELIMITER = "_";
    
        private Long versionDelta = Long.valueOf(-1);
    
        @XStreamImplicit
        private AbstractQueue<Application> applications;
    
        private Map<String, Application> appNameApplicationMap = new ConcurrentHashMap<String, Application>();
        private Map<String, AbstractQueue<InstanceInfo>> virtualHostNameAppMap = new ConcurrentHashMap<String, AbstractQueue<InstanceInfo>>();
        private Map<String, AbstractQueue<InstanceInfo>> secureVirtualHostNameAppMap = new ConcurrentHashMap<String, AbstractQueue<InstanceInfo>>();
        private Map<String, AtomicLong> virtualHostNameIndexMap = new ConcurrentHashMap<String, AtomicLong>();
        private Map<String, AtomicLong> secureVirtualHostNameIndexMap = new ConcurrentHashMap<String, AtomicLong>();
    
        private Map<String, AtomicReference<List<InstanceInfo>>> shuffleVirtualHostNameMap = new ConcurrentHashMap<String, AtomicReference<List<InstanceInfo>>>();
        private Map<String, AtomicReference<List<InstanceInfo>>> shuffledSecureVirtualHostNameMap = new ConcurrentHashMap<String, AtomicReference<List<InstanceInfo>>>();
    
        //其他代码省略。
    }