SpringCloud(第 049 篇)Netflix Eureka 源碼深入剖析(上)
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一、大致介紹
1、鑑於一些朋友的提問並提議講解下eureka的源碼分析,由此應運而產生的本章節的內容;
2、所以我站在自我的理解角度試着整理了這篇Eureka源碼的分析,希望對大家有所幫助;
3、由於篇幅太長不能在一篇裏面發佈出來,所以拆分了上下篇;
二、基本原理
1、Eureka Server 提供服務註冊服務,各個節點啓動後,會在Eureka Server中進行註冊,這樣Eureka Server中的服務註冊表中將會存儲所有可用服務節點的信息,服務節點的信息可以在界面中直觀的看到。
2、Eureka Client 是一個Java 客戶端,用於簡化與Eureka Server的交互,客戶端同時也具備一個內置的、使用輪詢負載算法的負載均衡器。
3、在應用啓動後,將會向Eureka Server發送心跳(默認週期爲30秒),如果Eureka Server在多個心跳週期沒有收到某個節點的心跳,Eureka Server 將會從服務註冊表中把這個服務節點移除(默認90秒)。
4、Eureka Server之間將會通過複製的方式完成數據的同步;
5、Eureka Client具有緩存的機制,即使所有的Eureka Server 都掛掉的話,客戶端依然可以利用緩存中的信息消費其它服務的API;
三、EurekaServer 啓動流程分析
3.1 跑一下 springms-discovery-eureka 代碼,不難發現,我們會看到一些有關 EurekaServer 啓動的流程日誌;
2017-10-22 18:14:17.635 INFO 5288 --- [ main] o.s.j.e.a.AnnotationMBeanExporter : Located managed bean 'environmentManager': registering with JMX server as MBean [org.springframework.cloud.context.environment:name=environmentManager,type=EnvironmentManager]
2017-10-22 18:14:17.650 INFO 5288 --- [ main] o.s.j.e.a.AnnotationMBeanExporter : Located managed bean 'restartEndpoint': registering with JMX server as MBean [org.springframework.cloud.context.restart:name=restartEndpoint,type=RestartEndpoint]
2017-10-22 18:14:17.661 INFO 5288 --- [ main] o.s.j.e.a.AnnotationMBeanExporter : Located managed bean 'refreshScope': registering with JMX server as MBean [org.springframework.cloud.context.scope.refresh:name=refreshScope,type=RefreshScope]
2017-10-22 18:14:17.674 INFO 5288 --- [ main] o.s.j.e.a.AnnotationMBeanExporter : Located managed bean 'configurationPropertiesRebinder': registering with JMX server as MBean [org.springframework.cloud.context.properties:name=configurationPropertiesRebinder,context=335b5620,type=ConfigurationPropertiesRebinder]
2017-10-22 18:14:17.683 INFO 5288 --- [ main] o.s.j.e.a.AnnotationMBeanExporter : Located managed bean 'refreshEndpoint': registering with JMX server as MBean [org.springframework.cloud.endpoint:name=refreshEndpoint,type=RefreshEndpoint]
2017-10-22 18:14:17.926 INFO 5288 --- [ main] o.s.c.support.DefaultLifecycleProcessor : Starting beans in phase 0
2017-10-22 18:14:17.927 INFO 5288 --- [ main] c.n.e.EurekaDiscoveryClientConfiguration : Registering application unknown with eureka with status UP
2017-10-22 18:14:17.927 INFO 5288 --- [ Thread-10] o.s.c.n.e.server.EurekaServerBootstrap : Setting the eureka configuration..
2017-10-22 18:14:17.948 INFO 5288 --- [ Thread-10] o.s.c.n.e.server.EurekaServerBootstrap : isAws returned false
2017-10-22 18:14:17.949 INFO 5288 --- [ Thread-10] o.s.c.n.e.server.EurekaServerBootstrap : Initialized server context
2017-10-22 18:14:17.949 INFO 5288 --- [ Thread-10] c.n.e.r.PeerAwareInstanceRegistryImpl : Got 1 instances from neighboring DS node
2017-10-22 18:14:17.949 INFO 5288 --- [ Thread-10] c.n.e.r.PeerAwareInstanceRegistryImpl : Renew threshold is: 1
2017-10-22 18:14:17.949 INFO 5288 --- [ Thread-10] c.n.e.r.PeerAwareInstanceRegistryImpl : Changing status to UP
2017-10-22 18:14:17.958 INFO 5288 --- [ Thread-10] e.s.EurekaServerInitializerConfiguration : Started Eureka Server
2017-10-22 18:14:18.019 INFO 5288 --- [ main] s.b.c.e.t.TomcatEmbeddedServletContainer : Tomcat started on port(s): 8761 (http)
2017-10-22 18:14:18.020 INFO 5288 --- [ main] c.n.e.EurekaDiscoveryClientConfiguration : Updating port to 8761
2017-10-22 18:14:18.023 INFO 5288 --- [ main] c.s.cloud.EurekaServerApplication : Started EurekaServerApplication in 8.299 seconds (JVM running for 8.886)
【【【【【【 Eureka微服務 】】】】】】已啓動.
【分析】:發現有這麼一句日誌打印“Setting the eureka configuration..”,eureka 開始進行配置,說不定也許就是Eureka Server 流程啓動的開
始呢?我們抱着懷疑的心態進入這行日誌打印的EurekaServerBootstrap類去看看。
3.2 進入 EurekaServerBootstrap 類看看,看這個類的名字,見名知意,應該就是 EurekaServer 的啓動類了;
protected void initEurekaEnvironment() throws Exception {
log.info("Setting the eureka configuration..");
。。。
}
【分析一】:我們看到日誌在 initEurekaEnvironment 方法中被打印出來,然後我順着這個方法尋找該方法被調用的地方;
public void contextInitialized(ServletContext context) {
try {
initEurekaEnvironment();
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);
}
}
【分析二】:接着發現 contextInitialized 這個方法裏面調用了 initEurekaEnvironment 方法,接着我們再往上層尋找被調用的地方;
【分析三】:接着我們看到 EurekaServerInitializerConfiguration 類中有個 start 方法,該方法創建了一個線程來後臺執行 EurekaServer 的初始化流程;
3.3 進入 EurekaServerInitializerConfiguration 方法,看看這個所謂的 EurekaServer 初始化配置做了哪些事情?
@Override
public void start() { // 打上斷點
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();
}
【分析一】:看到 log.info("Started Eureka Server"); 這行代碼,相信大家已經釋然了,這裏就是所謂的啓動了 EurekaServer 了,其實也就是
eurekaServerBootstrap.contextInitialized(EurekaServerInitializerConfiguration.this.servletContext) 初始化了一些我們未知的東西;
【分析二】:當打印完啓動Eureka Server日誌後,調用了兩次 publish 方法,該方法最終調用的是 this.applicationContext.publishEvent
(event) 方法,目的是利用Spring中ApplicationContext對事件傳遞性質,事件發佈者(applicationContext)來發布事件(event),但是缺少的是監聽
者,其實你仔細搜索下代碼,發現好像沒有地方對 EurekaServerStartedEvent、EurekaRegistryAvailableEvent 進行監聽,奇了怪了,這是咋了呢?
【分析三】:然後找到 EurekaServerStartedEvent 所在的目錄下,EurekaInstanceCanceledEvent、EurekaInstanceRegisteredEvent、
EurekaInstanceRenewedEvent、EurekaRegistryAvailableEvent、EurekaServerStartedEvent 有這麼幾個事件的類,服務下線事件、服務註冊事
件、服務續約事件、註冊中心啓動事件、Eureka Server啓動事件,這麼幾個事件都沒有被監聽,那麼我們是不是給添加上監聽,是不是就可以了呢?像這樣
@EventListener public void listen(EurekaInstanceCanceledEvent event) { 。。。處下線邏輯 },添加 EventListener 監聽註解,就可
以在我們自己的代碼邏輯中收到這個事件的回調了,所以想想SpringCloud還是挺機制的,提供回調接口讓我們自己實現自己的業務邏輯,真心不錯;
【分析四】:那麼反過來想想,爲啥會無緣無故 start 方法就被調用了呢?那麼反向繼續向上找調用 start 方法的地方,結果找到了
DefaultLifecycleProcessor類的doStart方法調用了 bean.start(); 這麼一段代碼;
3.4 進入 DefaultLifecycleProcessor 類看看,這個 EurekaServerInitializerConfiguration.start 方法是如何被觸發的?
private void doStart(Map<String, ? extends Lifecycle> lifecycleBeans, String beanName, boolean autoStartupOnly) {
// 打上斷點
Lifecycle bean = lifecycleBeans.remove(beanName);
if (bean != null && !this.equals(bean)) {
String[] dependenciesForBean = this.beanFactory.getDependenciesForBean(beanName);
for (String dependency : dependenciesForBean) {
doStart(lifecycleBeans, dependency, autoStartupOnly);
}
if (!bean.isRunning() &&
(!autoStartupOnly || !(bean instanceof SmartLifecycle) || ((SmartLifecycle) bean).isAutoStartup())) {
if (logger.isDebugEnabled()) {
logger.debug("Starting bean '" + beanName + "' of type [" + bean.getClass() + "]");
}
try {
bean.start();
}
catch (Throwable ex) {
throw new ApplicationContextException("Failed to start bean '" + beanName + "'", ex);
}
if (logger.isDebugEnabled()) {
logger.debug("Successfully started bean '" + beanName + "'");
}
}
}
}
【分析一】:看到在 bean.isRunning 等一系列狀態的判斷下才去調用 bean.start() 方法的,我們再往上尋找被調用地方;
public void start() {
// 打上斷點
if (this.members.isEmpty()) {
return;
}
if (logger.isInfoEnabled()) {
logger.info("Starting beans in phase " + this.phase);
}
Collections.sort(this.members);
for (LifecycleGroupMember member : this.members) {
if (this.lifecycleBeans.containsKey(member.name)) {
doStart(this.lifecycleBeans, member.name, this.autoStartupOnly);
}
}
}
【分析二】:該類是DefaultLifecycleProcessor中內部類LifecycleGroup的一個方法,再往上尋找調用方;
private void startBeans(boolean autoStartupOnly) {
Map<String, Lifecycle> lifecycleBeans = getLifecycleBeans();
Map<Integer, LifecycleGroup> phases = new HashMap<Integer, LifecycleGroup>();
for (Map.Entry<String, ? extends Lifecycle> entry : lifecycleBeans.entrySet()) {
Lifecycle bean = entry.getValue();
if (!autoStartupOnly || (bean instanceof SmartLifecycle && ((SmartLifecycle) bean).isAutoStartup())) {
int phase = getPhase(bean);
LifecycleGroup group = phases.get(phase);
if (group == null) {
group = new LifecycleGroup(phase, this.timeoutPerShutdownPhase, lifecycleBeans, autoStartupOnly);
phases.put(phase, group);
}
group.add(entry.getKey(), bean);
}
}
if (phases.size() > 0) {
List<Integer> keys = new ArrayList<Integer>(phases.keySet());
Collections.sort(keys);
for (Integer key : keys) {
phases.get(key).start();
}
}
}
【分析三】:startBeans 屬於 DefaultLifecycleProcessor 類的一個私有方法,startBeans 方法第一行就是獲取 getLifecycleBeans() 生命週期
Bean對象,由此可見似乎 Eureka Server 之所以會被啓動,是不是實現了某個接口或者重寫了某個方法,纔會導致由於容易在初始化的過程中因調用某些特
殊方法或者某些類才啓動的,因此我們回頭去看看 EurekaServerInitializerConfiguration 這個類;
【分析四】:結果發現 EurekaServerInitializerConfiguration 這個類實現了 SmartLifecycle 這麼樣的一個接口,而 SmartLifecycle 接口又繼
承了 Lifecycle 生命週期接口類,所以真想已經重見天日了,原來是實現了 Lifecycle 這樣的一個接口,然後實現了 start 方法,因此 Eureka
Server 就這麼稀裏糊塗的就被莫名其妙的啓動起來了?
3.5 到這裏難道就真的完了麼?難道Eureka Server啓動就幹這麼點點事情?不可能吧?
【分析一】:我們之前僅僅只是通過了日誌來逆向分析,但是我們是不是忘了我們本應該標誌是Eureka Server的這個註解了呢?沒錯,我們在分析的過程中
已經將 @EnableEurekaServer 這個註解遺忘了,那麼我們現在先回到這個註解類來看看;
3.6 進入 EnableEurekaServer 類,看看究竟幹了啥?
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Import(EurekaServerConfiguration.class)
public @interface EnableEurekaServer {
}
【分析一】:我們不難發現 EnableEurekaServer 類上有個 @Import 註解,引用了一個 class 文件,由此我們進入觀察;
3.7 進入 EurekaServerConfiguration 類看看,看名稱的話,理解的意思大概就是 Eureka Server 配置類;
【分析一】:果不其然,這個類有很多 @Bean、@Configuration 註解過的方法,那是不是我們可以認爲剛纔 3.1~3.4 的推論是不是就是由於被實例化了這麼一個 Bean,然後就慢慢的調用到了 start 方法了呢?
【分析二】:搜索 “Bootstrap” 字樣,還真發現了有這麼一個方法;
@Bean
public EurekaServerBootstrap eurekaServerBootstrap(PeerAwareInstanceRegistry registry,
EurekaServerContext serverContext) {
return new EurekaServerBootstrap(this.applicationInfoManager,
this.eurekaClientConfig, this.eurekaServerConfig, registry,
serverContext);
}
【分析三】:既然有這麼一個 Bean,那麼是不是和剛開始順着日誌逆向分析也是有一定道理的,沒有這麼一個Bean的存在,那麼 DefaultLifecycleProcessor.startBeans 方法中 getLifecycleBeans 的這個也就沒那麼順暢被找到了呢?不過我的猜想是這樣的,本人沒有將源碼下載下來,將 eurekaServerBootstrap 方法中的 @Bean 註解註釋掉試試,不過推理起來也八九不離十,這個疑問懸念就留給大家嘗試嘗試吧;
【分析四】:既然找到了一個 @Bean 註解過的方法,那我們再找找其他的一些被註解過的方法,比如一些通用全局用的類似詞眼,比如 Context,Bean,Init、Server 之類的;
@Bean
public EurekaServerContext eurekaServerContext(ServerCodecs serverCodecs,
PeerAwareInstanceRegistry registry, PeerEurekaNodes peerEurekaNodes) {
return new DefaultEurekaServerContext(this.eurekaServerConfig, serverCodecs,
registry, peerEurekaNodes, this.applicationInfoManager);
}
@Bean
public PeerEurekaNodes peerEurekaNodes(PeerAwareInstanceRegistry registry,
ServerCodecs serverCodecs) {
return new PeerEurekaNodes(registry, this.eurekaServerConfig,
this.eurekaClientConfig, serverCodecs, this.applicationInfoManager);
}
@Bean
public PeerAwareInstanceRegistry peerAwareInstanceRegistry(
ServerCodecs serverCodecs) {
this.eurekaClient.getApplications(); // force initialization
return new InstanceRegistry(this.eurekaServerConfig, this.eurekaClientConfig,
serverCodecs, this.eurekaClient,
this.instanceRegistryProperties.getExpectedNumberOfRenewsPerMin(),
this.instanceRegistryProperties.getDefaultOpenForTrafficCount());
}
@Bean
@ConditionalOnProperty(prefix = "eureka.dashboard", name = "enabled", matchIfMissing = true)
public EurekaController eurekaController() {
return new EurekaController(this.applicationInfoManager);
}
【分析五】:DefaultEurekaServerContext.initialize 初始化了一些東西,現在還不知道幹啥用的,先放這裏,打上斷點;
【分析六】:PeerEurekaNodes.start 方法,又是一個 start 方法,但是該類沒有實現任何類,姑且先放這裏,打上斷點;
【分析七】:InstanceRegistry.register 方法,而且還有幾個呢,可能是客戶端註冊用的,也先放這裏,都打上斷點,或者將 這個類的所有方法都斷點上,斷點打完後發現有註冊的,有續約的,有註銷的;
【分析八】:打完這些斷點後,感覺沒有思路了,索性就斷點跑一把,看看有什麼新的發現點;
3.8 停止服務,Debug 跑一下 springms-discovery-eureka 代碼;
【分析一】:DefaultEurekaServerContext.initialize 方法被調用了,證實了剛纔想法,EurekaServerConfiguration 不是白寫的,還是有它的作用的;
@PostConstruct
@Override
public void initialize() throws Exception {
logger.info("Initializing ...");
peerEurekaNodes.start();
registry.init(peerEurekaNodes);
logger.info("Initialized");
}
【分析二】:進入 initialize 方法中 peerEurekaNodes.start();
public void start() {
taskExecutor = Executors.newSingleThreadScheduledExecutor(
new ThreadFactory() {
@Override
public Thread newThread(Runnable r) {
Thread thread = new Thread(r, "Eureka-PeerNodesUpdater");
thread.setDaemon(true);
return thread;
}
}
);
try {
updatePeerEurekaNodes(resolvePeerUrls());
Runnable peersUpdateTask = new Runnable() {
@Override
public void run() {
try {
updatePeerEurekaNodes(resolvePeerUrls());
} catch (Throwable e) {
logger.error("Cannot update the replica Nodes", e);
}
}
};
// 註釋:間隔 600000 毫秒,即 10分鐘 間隔執行一次服務集羣數據同步;
taskExecutor.scheduleWithFixedDelay(
peersUpdateTask,
serverConfig.getPeerEurekaNodesUpdateIntervalMs(),
serverConfig.getPeerEurekaNodesUpdateIntervalMs(),
TimeUnit.MILLISECONDS
);
} catch (Exception e) {
throw new IllegalStateException(e);
}
for (PeerEurekaNode node : peerEurekaNodes) {
logger.info("Replica node URL: " + node.getServiceUrl());
}
}
【分析三】: start 方法中會看到一個定時調度的任務,updatePeerEurekaNodes(resolvePeerUrls()); 間隔 600000 毫秒,即 10分鐘 間隔執行一次服務集羣數據同步;
【分析四】: 然後斷點放走放下走,進入 initialize 方法中 registry.init(peerEurekaNodes);
@Override
public void init(PeerEurekaNodes peerEurekaNodes) throws Exception {
this.numberOfReplicationsLastMin.start();
this.peerEurekaNodes = peerEurekaNodes;
// 註釋:初始化 Eureka Server 響應緩存,默認緩存時間爲30s
initializedResponseCache();
// 註釋:定時任務,多久重置一下心跳閾值,900000 毫秒,即 15分鐘 的間隔時間,會重置心跳閾值
scheduleRenewalThresholdUpdateTask();
// 註釋:初始化遠端註冊
initRemoteRegionRegistry();
try {
Monitors.registerObject(this);
} catch (Throwable e) {
logger.warn("Cannot register the JMX monitor for the InstanceRegistry :", e);
}
}
【分析五】: 緩存也配置好了,定時任務也配置好了,似乎應該沒啥了,那麼我們把斷點放開,看看下一步會走到哪裏?
3.9 EurekaServerInitializerConfiguration.start 也進斷點了。
【分析一】:先是 DefaultLifecycleProcessor.doStart 方法進斷點,然後纔是 EurekaServerInitializerConfiguration.start 方法進斷點;
【分析二】:再一次證明剛剛的逆向分析僅僅只是缺了個從頭EnableEurekaServer分析罷了,但是最終方法論分析思路還是對的,由於開始分析過這裏,然而我們就跳過,繼續放開斷點向後繼續看看;
3.10 InstanceRegistry.openForTraffic 也進斷點了。
【分析一】:這不就是我們剛纔在 “步驟3.7之分析七” 打的斷點麼?看下堆棧信息,正是 “步驟3.2之分析一” 中 initEurekaServerContext 方法中有
這麼一句 this.registry.openForTraffic(this.applicationInfoManager, registryCount); 調用到了,因果輪迴,代碼千變萬化,打上斷點還有有好處的,結果還是回到了開始日誌逆向分析的地方。
【分析二】:進入 super.openForTraffic 方法;
@Override
public void openForTraffic(ApplicationInfoManager applicationInfoManager, int count) {
// Renewals happen every 30 seconds and for a minute it should be a factor of 2.
// 註釋:每30秒續約一次,那麼每分鐘續約就是2次,所以纔是 count * 2 的結果;
this.expectedNumberOfRenewsPerMin = count * 2;
this.numberOfRenewsPerMinThreshold =
(int) (this.expectedNumberOfRenewsPerMin * serverConfig.getRenewalPercentThreshold());
logger.info("Got " + count + " instances from neighboring DS node");
logger.info("Renew threshold is: " + numberOfRenewsPerMinThreshold);
this.startupTime = System.currentTimeMillis();
if (count > 0) {
this.peerInstancesTransferEmptyOnStartup = false;
}
DataCenterInfo.Name selfName = applicationInfoManager.getInfo().getDataCenterInfo().getName();
boolean isAws = Name.Amazon == selfName;
if (isAws && serverConfig.shouldPrimeAwsReplicaConnections()) {
logger.info("Priming AWS connections for all replicas..");
primeAwsReplicas(applicationInfoManager);
}
logger.info("Changing status to UP");
// 註釋:修改 Eureka Server 爲上電狀態,就是說設置 Eureka Server 已經處於活躍狀態了,那就是意味着 EurekaServer 基本上說可以正常使用了;
applicationInfoManager.setInstanceStatus(InstanceStatus.UP);
// 註釋:定時任務,60000 毫秒,即 1分鐘 的間隔時間,Eureke Server定期進行失效節點的清理
super.postInit();
}
【分析三】:這裏主要設置了服務狀態,以及開啓了定時清理失效節點的定時任務,每分鐘掃描一次;
3.11 繼續放開斷點,來到了日誌打印 “main] c.n.e.EurekaDiscoveryClientConfiguration : Updating port to 8761” 的EurekaDiscoveryClientConfiguration 類中 onApplicationEvent 方法。
@EventListener(EmbeddedServletContainerInitializedEvent.class)
public void onApplicationEvent(EmbeddedServletContainerInitializedEvent event) {
// TODO: take SSL into account when Spring Boot 1.2 is available
int localPort = event.getEmbeddedServletContainer().getPort();
if (this.port.get() == 0) {
log.info("Updating port to " + localPort);
this.port.compareAndSet(0, localPort);
start();
}
}
【分析一】:設置端口,當看到 Updating port to 8761 這樣的日誌打印出來的話,說明 Eureka Server 整個啓動也就差不多Over了。現在回頭看看,
發現分析了不少的方法和流程,有種感覺被掏空的感覺了。
3.12 總結 EurekaServer 啓動時候大概幹了哪些事情?
1、初始化Eureka環境,Eureka上下文;
2、初始化EurekaServer的緩存
3、啓動了一些定時任務,比如充值心跳閾值定時任務,清理失效節點定時任務;
4、更新EurekaServer上電狀態,更新EurekaServer端口;
雖然我從列舉的流程裏面大概總結了這麼幾點,但是還是有些是我沒關注到的,如果大家有關注到的,可以和我共同討論分析分析。
四、EurekaServer 處理服務註冊、集羣數據複製
4.1 EurekaClient 是如何註冊到 EurekaServer 的?
【分析一】:由於我們剛纔在 org.springframework.cloud.netflix.eureka.server.InstanceRegistry 的每個方法都打了一個斷點,而且現在
EurekaServer 已經處於 Debug 運行狀態,那麼我們就隨便找一個被 @EnableEurekaClient 的微服務啓動試試,要麼就拿 springms-provider-user
微服務來試試吧,直接 Run。
【分析二】:猜測,如果如我們分析所想,當 springms-provider-user 啓動後,就一定會調用註冊register方法,那麼就接着往下看,拭目以待;
4.2 InstanceRegistry.register(final InstanceInfo info, final boolean isReplication) 方法進斷點了。
【分析一】:由於 InstanceRegistry.register 是我們剛剛打斷點的地方,那麼我們順着堆棧信息往上看,原來是 ApplicationResource.addInstance 方法被調用了,那麼我們就看看 addInstance 這個方法,並在 addInstance 這裏打上斷點;接着我們重新殺死 springms-provider-user 服務,然後再重啓 springms-provider-user 服務;
4.2 斷點再次來到了 ApplicationResource 類,這個類呢,主要是處理接收 Http 的服務請求。
@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.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
}
【分析一】:這裏的寫法貌似看起來和我們之前 Controller 的 RESTFUL 寫法有點不一樣,仔細一看,原來是Jersey RESTful 框架,是一個產品級的
RESTful service 和 client 框架。與Struts類似,它同樣可以和hibernate,spring框架整合。
【分析二】:緊接着,我們看到 registry.register(info, "true".equals(isReplication)); 這麼一段代碼,註冊啊,原來EurekaClient客戶端啓
動後會調用會通過Http(s)請求,直接調到 ApplicationResource.addInstance 方法,那麼總算明白了,只要是和註冊有關的,都會調用這個方法。
【分析三】:接着我們深入 registry.register(info, "true".equals(isReplication)) 查看;
@Override
public void register(final InstanceInfo info, final boolean isReplication) {
handleRegistration(info, resolveInstanceLeaseDuration(info), isReplication);
super.register(info, isReplication);
}
【分析四】:看看 handleRegistration(info, resolveInstanceLeaseDuration(info), isReplication) 方法;
private void handleRegistration(InstanceInfo info, int leaseDuration,
boolean isReplication) {
log("register " + info.getAppName() + ", vip " + info.getVIPAddress()
+ ", leaseDuration " + leaseDuration + ", isReplication "
+ isReplication);
publishEvent(new EurekaInstanceRegisteredEvent(this, info, leaseDuration,
isReplication));
}
【分析五】:該方法僅僅只是打了一個日誌,然後通過 ApplicationContext 發佈了一個事件 EurekaInstanceRegisteredEvent 服務註冊事件,正如
“步驟3.3之分析三” 所提到的,用戶可以給 EurekaInstanceRegisteredEvent 添加監聽事件,那麼用戶就可以在此刻實現自己想要的一些業務邏輯。
然後我們再來看看 super.register(info, isReplication) 方法,該方法是 InstanceRegistry 的父類 PeerAwareInstanceRegistryImpl 的方法。
4.3 進入 PeerAwareInstanceRegistryImpl 類的 register(final InstanceInfo info, final boolean isReplication) 方法;
@Override
public void register(final InstanceInfo info, final boolean isReplication) {
// 註釋:續約時間,默認時間是常量值 90 秒
int leaseDuration = Lease.DEFAULT_DURATION_IN_SECS;
// 註釋:續約時間,當然也可以從配置文件中取出來,所以說續約時間值也是可以讓我們自己自定義配置的
if (info.getLeaseInfo() != null && info.getLeaseInfo().getDurationInSecs() > 0) {
leaseDuration = info.getLeaseInfo().getDurationInSecs();
}
// 註釋:將註冊方的信息寫入 EurekaServer 的註冊表,父類爲 AbstractInstanceRegistry
super.register(info, leaseDuration, isReplication);
// 註釋:EurekaServer 節點之間的數據同步,複製到其他Peer
replicateToPeers(Action.Register, info.getAppName(), info.getId(), info, null, isReplication);
}
【分析一】:進入 super.register(info, leaseDuration, isReplication) 看看是如何寫入 EurekaServer 的註冊表的,即進入 AbstractInstanceRegistry.register(InstanceInfo registrant, int leaseDuration, boolean isReplication) 方法。
public void register(InstanceInfo registrant, int leaseDuration, boolean isReplication) {
try {
read.lock();
// 註釋:registry 這個變量,就是我們所謂的註冊表,註冊表是保存在內存中的;
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);
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);
synchronized (recentRegisteredQueue) {
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);
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();
}
}
【分析二】:發現這個方法有點長,大致閱讀,主要更新了註冊表的時間之外,還更新了緩存等其它東西,大家有興趣的可以深究閱讀該方法;
4.4 跳出來我們接着看上面的 replicateToPeers(Action.Register, info.getAppName(), info.getId(), info, null, isReplication) 的這個方法。
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
// 註釋:如果已經複製過,就不再複製
if (peerEurekaNodes == Collections.EMPTY_LIST || isReplication) {
return;
}
// 遍歷Eureka Server集羣中的所有節點,進行復制操作
for (final PeerEurekaNode node : peerEurekaNodes.getPeerEurekaNodes()) {
// If the url represents this host, do not replicate to yourself.
if (peerEurekaNodes.isThisMyUrl(node.getServiceUrl())) {
continue;
}
// 沒有複製過,遍歷Eureka Server集羣中的node節點,依次操作,包括取消、註冊、心跳、狀態更新等。
replicateInstanceActionsToPeers(action, appName, id, info, newStatus, node);
}
} finally {
tracer.stop();
}
}
【分析一】:走到這裏,我不難理解,每當有註冊請求,首先更新 EurekaServer 的註冊表,然後再將信息同步到其它EurekaServer的節點上去;
【分析二】:接下來我們看看 node 節點是如何進行復制操作的,進入 replicateInstanceActionsToPeers 方法。
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);
}
}
【分析三】:節點之間的複製狀態操作,都在這裏體現的淋漓盡致,那麼我們就拿 Register 類型 node.register(info) 來看,我們來看看 node 究竟是
如何做到同步信息的,進入 node.register(info) 方法看看;
4.5 進入 PeerEurekaNode.register(final InstanceInfo info) 方法,一窺究竟如何同步數據。
public void register(final InstanceInfo info) throws Exception {
// 註釋:任務過期時間給任務分發器處理,默認時間偏移當前時間 30秒
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
);
}
【分析一】:這裏涉及到了 Eureka 的任務批處理,通常情況下Peer之間的同步需要調用多次,如果EurekaServer一多的話,那麼將會有很多http請求,所
以自然而然的孕育出了任務批處理,但是也在一定程度上導致了註冊和下線的一些延遲,突出優勢的同時也勢必會造成一些劣勢,但是這些延遲情況還是能符合
常理在容忍範圍之內的。
【分析二】:在 expiryTime 超時時間之內,批次處理要做的事情就是合併任務爲一個List,然後發送請求的時候,將這個批次List直接打包發送請求出去,這樣的話,在這個批次的List裏面,可能包含取消、註冊、心跳、狀態等一系列狀態的集合List。
【分析三】:我們再接着看源碼,batchingDispatcher.process 這麼一調用,然後我們就直接看這個 TaskDispatchers.createBatchingTaskDispatcher 方法。
public static <ID, T> TaskDispatcher<ID, T> createBatchingTaskDispatcher(String id,
int maxBufferSize,
int workloadSize,
int workerCount,
long maxBatchingDelay,
long congestionRetryDelayMs,
long networkFailureRetryMs,
TaskProcessor<T> taskProcessor) {
final AcceptorExecutor<ID, T> acceptorExecutor = new AcceptorExecutor<>(
id, maxBufferSize, workloadSize, maxBatchingDelay, congestionRetryDelayMs, networkFailureRetryMs
);
final TaskExecutors<ID, T> taskExecutor = TaskExecutors.batchExecutors(id, workerCount, taskProcessor, acceptorExecutor);
return new TaskDispatcher<ID, T>() {
@Override
public void process(ID id, T task, long expiryTime) {
acceptorExecutor.process(id, task, expiryTime);
}
@Override
public void shutdown() {
acceptorExecutor.shutdown();
taskExecutor.shutdown();
}
};
}
【分析四】:這裏的 process 方法會將任務添加到隊列中,有入隊列自然有出隊列,具體怎麼取任務,我就不一一給大家講解了,我就講講最後是怎麼觸發任務的。進入 final TaskExecutors<ID, T> taskExecutor = TaskExecutors.batchExecutors(id, workerCount, taskProcessor, acceptorExecutor) 這句代碼的 TaskExecutors.batchExecutors 方法。
static <ID, T> TaskExecutors<ID, T> batchExecutors(final String name,
int workerCount,
final TaskProcessor<T> processor,
final AcceptorExecutor<ID, T> acceptorExecutor) {
final AtomicBoolean isShutdown = new AtomicBoolean();
final TaskExecutorMetrics metrics = new TaskExecutorMetrics(name);
return new TaskExecutors<>(new WorkerRunnableFactory<ID, T>() {
@Override
public WorkerRunnable<ID, T> create(int idx) {
return new BatchWorkerRunnable<>("TaskBatchingWorker-" +name + '-' + idx, isShutdown, metrics, processor, acceptorExecutor);
}
}, workerCount, isShutdown);
}
【分析五】:我們發現 TaskExecutors 類中的 batchExecutors 這個靜態方法,有個 BatchWorkerRunnable 返回的實現類,因此我們再次進入 BatchWorkerRunnable 類看看究竟,而且既然是 Runnable,那麼勢必會有 run 方法。
@Override
public void run() {
try {
while (!isShutdown.get()) {
// 註釋:獲取信號量釋放 batchWorkRequests.release(),返回任務集合列表
List<TaskHolder<ID, T>> holders = getWork();
metrics.registerExpiryTimes(holders);
List<T> tasks = getTasksOf(holders);
// 註釋:將批量任務打包請求Peer節點
ProcessingResult result = processor.process(tasks);
switch (result) {
case Success:
break;
case Congestion:
case TransientError:
taskDispatcher.reprocess(holders, result);
break;
case PermanentError:
logger.warn("Discarding {} tasks of {} due to permanent error", holders.size(), workerName);
}
metrics.registerTaskResult(result, tasks.size());
}
} catch (InterruptedException e) {
// Ignore
} catch (Throwable e) {
// Safe-guard, so we never exit this loop in an uncontrolled way.
logger.warn("Discovery WorkerThread error", e);
}
}
【分析六】:這就是我們 BatchWorkerRunnable 類的 run 方法,這裏面首先要獲取信號量釋放,才能獲得任務集合,一旦獲取到了任務集合的話,那麼就直接調用 processor.process(tasks) 方法請求 Peer 節點同步數據,接下來我們看看 ReplicationTaskProcessor.process 方法;
@Override
public ProcessingResult process(List<ReplicationTask> tasks) {
ReplicationList list = createReplicationListOf(tasks);
try {
// 註釋:這裏通過 JerseyReplicationClient 客戶端對象直接發送list請求數據
EurekaHttpResponse<ReplicationListResponse> response = replicationClient.submitBatchUpdates(list);
int statusCode = response.getStatusCode();
if (!isSuccess(statusCode)) {
if (statusCode == 503) {
logger.warn("Server busy (503) HTTP status code received from the peer {}; rescheduling tasks after delay", peerId);
return ProcessingResult.Congestion;
} else {
// Unexpected error returned from the server. This should ideally never happen.
logger.error("Batch update failure with HTTP status code {}; discarding {} replication tasks", statusCode, tasks.size());
return ProcessingResult.PermanentError;
}
} else {
handleBatchResponse(tasks, response.getEntity().getResponseList());
}
} catch (Throwable e) {
if (isNetworkConnectException(e)) {
logNetworkErrorSample(null, e);
return ProcessingResult.TransientError;
} else {
logger.error("Not re-trying this exception because it does not seem to be a network exception", e);
return ProcessingResult.PermanentError;
}
}
return ProcessingResult.Success;
}
【分析七】:感覺快要見到真相了,所以我們迫不及待的進入 JerseyReplicationClient.submitBatchUpdates(ReplicationList replicationList) 方法一窺究竟。
@Override
public EurekaHttpResponse<ReplicationListResponse> submitBatchUpdates(ReplicationList replicationList) {
ClientResponse response = null;
try {
response = jerseyApacheClient.resource(serviceUrl)
// 註釋:這纔是重點,請求目的相對路徑,peerreplication/batch/
.path(PeerEurekaNode.BATCH_URL_PATH)
.accept(MediaType.APPLICATION_JSON_TYPE)
.type(MediaType.APPLICATION_JSON_TYPE)
.post(ClientResponse.class, replicationList);
if (!isSuccess(response.getStatus())) {
return anEurekaHttpResponse(response.getStatus(), ReplicationListResponse.class).build();
}
ReplicationListResponse batchResponse = response.getEntity(ReplicationListResponse.class);
return anEurekaHttpResponse(response.getStatus(), batchResponse).type(MediaType.APPLICATION_JSON_TYPE).build();
} finally {
if (response != null) {
response.close();
}
}
}
【分析八】:看到了相對路徑地址,我們搜索下"batch"這樣的字符串看看有沒有對應的接收方法或者被@Path註解進入的;在 eureka-core-1.4.12.jar 這個包下面,果然搜到到了 @Path("batch") 這樣的字樣,直接進入,發現這是 PeerReplicationResource 類的方法 batchReplication,我們進入這方法看看。
@Path("batch")
@POST
public Response batchReplication(ReplicationList replicationList) {
try {
ReplicationListResponse batchResponse = new ReplicationListResponse();
// 註釋:這裏將收到的任務列表,依次循環解析處理,主要核心方法在 dispatch 方法中。
for (ReplicationInstance instanceInfo : replicationList.getReplicationList()) {
try {
batchResponse.addResponse(dispatch(instanceInfo));
} catch (Exception e) {
batchResponse.addResponse(new ReplicationInstanceResponse(Status.INTERNAL_SERVER_ERROR.getStatusCode(), null));
logger.error(instanceInfo.getAction() + " request processing failed for batch item "
+ instanceInfo.getAppName() + '/' + instanceInfo.getId(), e);
}
}
return Response.ok(batchResponse).build();
} catch (Throwable e) {
logger.error("Cannot execute batch Request", e);
return Response.status(Status.INTERNAL_SERVER_ERROR).build();
}
}
【分析九】:看到了循環一次遍歷任務進行處理,不知不覺覺得心花怒放,勝利的重點馬上就要到來了,我們進入 PeerReplicationResource.dispatch 方法看看。
private ReplicationInstanceResponse dispatch(ReplicationInstance instanceInfo) {
ApplicationResource applicationResource = createApplicationResource(instanceInfo);
InstanceResource resource = createInstanceResource(instanceInfo, applicationResource);
String lastDirtyTimestamp = toString(instanceInfo.getLastDirtyTimestamp());
String overriddenStatus = toString(instanceInfo.getOverriddenStatus());
String instanceStatus = toString(instanceInfo.getStatus());
Builder singleResponseBuilder = new Builder();
switch (instanceInfo.getAction()) {
case Register:
singleResponseBuilder = handleRegister(instanceInfo, applicationResource);
break;
case Heartbeat:
singleResponseBuilder = handleHeartbeat(resource, lastDirtyTimestamp, overriddenStatus, instanceStatus);
break;
case Cancel:
singleResponseBuilder = handleCancel(resource);
break;
case StatusUpdate:
singleResponseBuilder = handleStatusUpdate(instanceInfo, resource);
break;
case DeleteStatusOverride:
singleResponseBuilder = handleDeleteStatusOverride(instanceInfo, resource);
break;
}
return singleResponseBuilder.build();
}
【分析十】:隨便抓一個類型,那我們也拿 Register 類型來看,進入 PeerReplicationResource.handleRegister 看看。
private static Builder handleRegister(ReplicationInstance instanceInfo, ApplicationResource applicationResource) {
// 註釋:private static final String REPLICATION = "true"; 定義的一個常量值,而且還是回調 ApplicationResource.addInstance 方法
applicationResource.addInstance(instanceInfo.getInstanceInfo(), REPLICATION);
return new Builder().setStatusCode(Status.OK.getStatusCode());
}
【分析十一】:Peer節點的同步旅程終於結束了,最終又回調到了 ApplicationResource.addInstance 這個方法,這個方法在最終是EurekaClient啓動後註冊調用的方法,然而Peer節點的信息同步也調用了這個方法,僅僅只是通過一個變量 isReplication 爲true還是false來判斷是否是節點複製。剩下的ApplicationResource.addInstance流程前面已經提到過了,相信大家已經明白了註冊的流程是如何扭轉的,包括批量任務是如何處理EurekaServer節點之間的信息同步的了。
五、EurekaClient 啓動流程分析
詳見 SpringCloud(第 050 篇)Netflix Eureka 源碼深入剖析(下)
六、下載地址
https://gitee.com/ylimhhmily/SpringCloudTutorial.git
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