02、EurekaServer自我保护源码分析

修改续租时间会打破自我保护机制
https://github.com/spring-cloud/spring-cloud-netflix/issues/373

1.appName配置@EnableEurekaServer

@SpringBootApplication
@EnableEurekaServer
@RestController
public class Application {
	
	@RequestMapping("ping")
	public String ping() {
		return "hello eureka";
	}

	public static void main(String[] args) {
		SpringApplication.run(Application.class, args);
	}

}

2.EnableEurekaServer中引入了@Import(EurekaServerConfiguration.class)

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Import(EurekaServerConfiguration.class)
public @interface EnableEurekaServer {

}

3.EurekaServerConfiguration中引入EurekaServerInitializerConfiguration

@Configuration
@Import(EurekaServerInitializerConfiguration.class)
@EnableDiscoveryClient
@EnableConfigurationProperties(EurekaDashboardProperties.class)
@PropertySource("classpath:/eureka/server.properties")
public class EurekaServerConfiguration extends WebMvcConfigurerAdapter {

4.EurekaServerInitializerConfiguration实现了SmartLifecycle，再所有bean都被初始化后执行start()方法。

当bean都被注册完成后，会调用SmartLifecycle的start()方法。

@CommonsLog
public class EurekaServerInitializerConfiguration
		implements ServletContextAware, SmartLifecycle, Ordered {

5.EurekaServerInitializerConfiguration的start()中调用了EurekaServerBootstrap的contextInitialized()方法。

@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();
	}

6.EurekaServerBootstrap的contextInitialized()方法中调用了initEurekaServerContext，initEurekaServerContext调用了PeerAwareInstanceRegistry的openForTraffic方法

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);
		}
	}

protected void initEurekaServerContext() throws Exception {
		// For backward compatibility
		JsonXStream.getInstance().registerConverter(new V1AwareInstanceInfoConverter(),
				XStream.PRIORITY_VERY_HIGH);
		XmlXStream.getInstance().registerConverter(new V1AwareInstanceInfoConverter(),
				XStream.PRIORITY_VERY_HIGH);

		if (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");

		// Copy registry from neighboring eureka node
		int registryCount = this.registry.syncUp();
		this.registry.openForTraffic(this.applicationInfoManager, registryCount);

		// Register all monitoring statistics.
		EurekaMonitors.registerAllStats();
	}

7.openForTraffic代码计算expectedNumberOfRenewsPerMin、numberOfRenewsPerMinThreshold

@Override
public void openForTraffic(ApplicationInfoManager applicationInfoManager, int count) {
    // Renewals happen every 30 seconds and for a minute it should be a factor of 2.
    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");
    applicationInfoManager.setInstanceStatus(InstanceStatus.UP);
    super.postInit();
}

9.AbstractInstanceRegistry启动剔除定时器super.postInit()

protected void postInit() {
    renewsLastMin = new MeasuredRate(1000 * 60 * 1);
    if (evictionTaskRef.get() != null) {
        evictionTaskRef.get().cancel();
    }
    evictionTaskRef.set(new EvictionTask());
    evictionTimer.schedule(evictionTaskRef.get(),
            serverConfig.getEvictionIntervalTimerInMs(),
            serverConfig.getEvictionIntervalTimerInMs());
}

10.numberOfRenewsPerMinThreshold 每分钟续租的阀值

this.expectedNumberOfRenewsPerMin = count * 2;
numberOfRenewsPerMinThreshold  每分钟获取的续约数的阀值
this.numberOfRenewsPerMinThreshold = (int) (this.expectedNumberOfRenewsPerMin * serverConfig.getRenewalPercentThreshold());

11.剔除服务

@Override
public boolean isLeaseExpirationEnabled() {
    if (!isSelfPreservationModeEnabled()) {
        // The self preservation mode is disabled, hence allowing the instances to expire.
        return true;
    }
    return numberOfRenewsPerMinThreshold > 0 && getNumOfRenewsInLastMin() > numberOfRenewsPerMinThreshold;
}

public void evict(long additionalLeaseMs) {
        logger.debug("Running the evict task");

        if (!isLeaseExpirationEnabled()) {
            logger.debug("DS: lease expiration is currently disabled.");
            return;
        }
   。。。。。。。

12.当每分钟收到续租的个小于等于每分钟收到续租数的阀值时，不做剔除。

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