Spring中Eureka的自我保护详解

public void evict(long additionalLeaseMs) {
        logger.debug("Running the evict task");
 
        //是否允许主动摘除故障的服务实例
        if (!isLeaseExpirationEnabled()) {
            logger.debug("DS: lease expiration is currently disabled.");
            return;
        }
 
       ....
 }

@Override
    public boolean isLeaseExpirationEnabled() {
        //默认是true，关闭自我保护机制的话，这个方法永远返回true，随时都可以清除故障的服务实例。
        if (!isSelfPreservationModeEnabled()) {
            // The self preservation mode is disabled, hence allowing the instances to expire.
            return true;
        }
        //numberOfRenewsPerMinThreshold  这个是我期望的一分钟发送多少心跳。
        //getNumOfRenewsInLastMin 这个是上一分钟一共发来多少心跳
        return numberOfRenewsPerMinThreshold > 0 && getNumOfRenewsInLastMin() > numberOfRenewsPerMinThreshold;
    }

// EurekaBootStrap.java
protected void initEurekaServerContext() throws Exception {
 
    // ... 省略其它代码
 
    // 【2.2.10】从其他 Eureka-Server 拉取注册信息
    // Copy registry from neighboring eureka node
    int registryCount = registry.syncUp();
    registry.openForTraffic(applicationInfoManager, registryCount);
    
    // ... 省略其它代码
}
 
// PeerAwareInstanceRegistryImpl.java
@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());

protected void updateRenewsPerMinThreshold() {
        this.numberOfRenewsPerMinThreshold = (int) (this.expectedNumberOfClientsSendingRenews
                * (60.0 / serverConfig.getExpectedClientRenewalIntervalSeconds())
                * serverConfig.getRenewalPercentThreshold());
    }

// PeerAwareInstanceRegistryImpl.java
private void scheduleRenewalThresholdUpdateTask() {
   timer.schedule(new TimerTask() {
                      @Override
                      public void run() {
                          updateRenewalThreshold();
                      }
                  }, serverConfig.getRenewalThresholdUpdateIntervalMs(),
           serverConfig.getRenewalThresholdUpdateIntervalMs());
}
 
// AbstractInstanceRegistry.java
/**
* 自我保护机锁
*
* 当计算如下参数时使用：
*  1. {@link #numberOfRenewsPerMinThreshold}
*  2. {@link #expectedNumberOfRenewsPerMin}
*/
protected final Object lock = new Object();
 
private void updateRenewalThreshold() {
   try {
       // 计算 应用实例数
       Applications apps = eurekaClient.getApplications();
       int count = 0;
       for (Application app : apps.getRegisteredApplications()) {
           for (InstanceInfo instance : app.getInstances()) {
               if (this.isRegisterable(instance)) {
                   ++count;
               }
           }
       }
       // 计算 expectedNumberOfRenewsPerMin 、 numberOfRenewsPerMinThreshold 参数
       synchronized (lock) {
           // Update threshold only if the threshold is greater than the
           // current expected threshold of if the self preservation is disabled.
           if ((count * 2) > (serverConfig.getRenewalPercentThreshold() * numberOfRenewsPerMinThreshold)
                   || (!this.isSelfPreservationModeEnabled())) {
               this.expectedNumberOfRenewsPerMin = count * 2;
               this.numberOfRenewsPerMinThreshold = (int) ((count * 2) * serverConfig.getRenewalPercentThreshold());
           }
       }
       logger.info("Current renewal threshold is : {}", numberOfRenewsPerMinThreshold);
   } catch (Throwable e) {
       logger.error("Cannot update renewal threshold", e);
   }
}