eureka.client.service-url.defaultZone=
http://localhost:8761/eureka,http://localhost:8762/eureka,http://localhost:8763/eureka,http://localhost:8764/eureka

@Override
  protected <R> EurekaHttpResponse<R> execute(RequestExecutor<R> requestExecutor) {
      List<EurekaEndpoint> candidateHosts = null;
      int endpointIdx = 0;
      for (int retry = 0; retry < numberOfRetries; retry++) {
          EurekaHttpClient currentHttpClient = delegate.get();
          EurekaEndpoint currentEndpoint = null;
          if (currentHttpClient == null) {
              if (candidateHosts == null) {
                  candidateHosts = getHostCandidates();
                  if (candidateHosts.isEmpty()) {
                      throw new TransportException("There is no known eureka server; cluster server list is empty");
                  }
              }
              if (endpointIdx >= candidateHosts.size()) {
                  throw new TransportException("Cannot execute request on any known server");
              }
              currentEndpoint = candidateHosts.get(endpointIdx++);
              currentHttpClient = clientFactory.newClient(currentEndpoint);
          }
          try {
              EurekaHttpResponse<R> response = requestExecutor.execute(currentHttpClient);
              if (serverStatusEvaluator.accept(response.getStatusCode(), requestExecutor.getRequestType())) {
                  delegate.set(currentHttpClient);
                  if (retry > 0) {
                      logger.info("Request execution succeeded on retry #{}", retry);
                  }
                  return response;
              }
              logger.warn("Request execution failure with status code {}; retrying on another server if available", response.getStatusCode());
          } catch (Exception e) {
              logger.warn("Request execution failed with message: {}", e.getMessage());  // just log message as the underlying client should log the stacktrace
          }
          // Connection error or 5xx from the server that must be retried on another server
          delegate.compareAndSet(currentHttpClient, null);
          if (currentEndpoint != null) {
              quarantineSet.add(currentEndpoint);
          }
      }
      throw new TransportException("Retry limit reached; giving up on completing the request");
  }

int endpointIdx = 0;
//用來(lái)保存所有Eureka Server信息(8761、8762、8763、8764)
List<EurekaEndpoint> candidateHosts = null;
//numberOfRetries的值代碼寫死默認(rèn)為3次
for (int retry = 0; retry < numberOfRetries; retry++) {
    /**
     *首次進(jìn)入循環(huán)時(shí)，獲取全量的Eureka Server信息(8761、8762、8763、8764)
     */
    if (candidateHosts == null) {
        candidateHosts = getHostCandidates();
    }
    /**
     *通過(guò)endpointIdx自增，依次獲取Eureka Server信息，然后發(fā)送
     *注冊(cè)的Post請(qǐng)求.
     */
    currentEndpoint = candidateHosts.get(endpointIdx++);
    currentHttpClient = clientFactory.newClient(currentEndpoint);
    try {
       /**
         *發(fā)送注冊(cè)的Post請(qǐng)求動(dòng)作，注意如果成功，則跳出循環(huán)，如果失敗則
         *根據(jù)endpointIdx依次獲取下一個(gè)Eureka Server.
         */
        response = requestExecutor.execute(currentHttpClient);
        return respones;
    } catch (Exception e) {
        //向注冊(cè)中心(Eureka Server)發(fā)起注冊(cè)的post出現(xiàn)異常時(shí)，打印日志...
    }
    //如果此次注冊(cè)動(dòng)作失敗，將當(dāng)前的信息保存到quarantineSet中(一個(gè)Set集合)
    if (currentEndpoint != null) {
        quarantineSet.add(currentEndpoint);
    }
}
//如果都失敗,則以異常形式拋出...
throw new TransportException("Retry limit reached; giving up on completing the request");

? ? private List<EurekaEndpoint> getHostCandidates() {
? ? ? ? List<EurekaEndpoint> candidateHosts = clusterResolver.getClusterEndpoints();
? ? ? ? quarantineSet.retainAll(candidateHosts);
? ? ? ? // If enough hosts are bad, we have no choice but start over again
? ? ? ? int threshold = (int) (candidateHosts.size() * transportConfig.getRetryableClientQuarantineRefreshPercentage());
? ? ? ? if (quarantineSet.isEmpty()) {
? ? ? ? ? ? // no-op
? ? ? ? } else if (quarantineSet.size() >= threshold) {
? ? ? ? ? ? logger.debug("Clearing quarantined list of size {}", quarantineSet.size());
? ? ? ? ? ? quarantineSet.clear();
? ? ? ? } else {
? ? ? ? ? ? List<EurekaEndpoint> remainingHosts = new ArrayList<>(candidateHosts.size());
? ? ? ? ? ? for (EurekaEndpoint endpoint : candidateHosts) {
? ? ? ? ? ? ? ? if (!quarantineSet.contains(endpoint)) {
? ? ? ? ? ? ? ? ? ? remainingHosts.add(endpoint);
? ? ? ? ? ? ? ? }
? ? ? ? ? ? }
? ? ? ? ? ? candidateHosts = remainingHosts;
? ? ? ? }
? ? ? ? return candidateHosts;
? ? }

private List<EurekaEndpoint> getHostCandidates() {
? ? /**
? ? ?* 獲取所有defaultZone配置的注冊(cè)中心信息(Eureka Server)，
? ? ?* 在本文例子中代表4個(gè)(8761、8762、8763、8764)Eureka Server
? ? ?*/
? ? List candidateHosts = clusterResolver.getClusterEndpoints();
? ? /**
? ? ?* quarantineSet這個(gè)Set集合中保存的是不可用的Eureka Server
? ? ?* 此處是拿不可用的Eureka Server與全量的Eureka Server取交集
? ? ?*/
? ? quarantineSet.retainAll(candidateHosts);
? ? /**
? ? ?* 根據(jù)RetryableClientQuarantineRefreshPercentage參數(shù)計(jì)算閾值
? ? ?* 該閾值后續(xù)會(huì)和quarantineSet中保存的不可用的Eureka Server個(gè)數(shù)
? ? ?* 作比較，從而判斷是否返回全量的Eureka Server還是過(guò)濾掉不可用的
? ? ?* Eureka Server。
? ? ?*/
? ? int threshold =?
? ? ? ?(int) (
? ? ? ? candidateHosts.size()
? ? ? ? ? ? ? *
? ? ? ? transportConfig.getRetryableClientQuarantineRefreshPercentage()
? ? ? ? );
? ? if (quarantineSet.isEmpty()) {
? ? ? ? /**
? ? ? ? ?* 首次進(jìn)入的時(shí)候，此時(shí)quarantineSet為空，直接返回全量的
? ? ? ? ?* Eureka Server列表
? ? ? ? ?*/
? ? } else if (quarantineSet.size() >= threshold) {
? ? ? ? /**
? ? ? ? ?* 將不可用的Eureka Server與threshold值相比較，如果不可
? ? ? ? ?* 用的Eureka Server個(gè)數(shù)大于閾值，則將之前保存的Eureka
? ? ? ? ?* Server內(nèi)容直接清空，并返回全量的Eureka Server列表。
? ? ? ? ?*/
? ? ? ? quarantineSet.clear();
? ? } else {
? ? ? ? /**
? ? ? ? ?* 通過(guò)quarantineSet集合保存不可用的Eureka Server來(lái)過(guò)濾
? ? ? ? ?* 全量的EurekaServer，從而獲取此次Eureka Client要注冊(cè)要
? ? ? ? ?* 注冊(cè)的Eureka Server實(shí)例地址。
? ? ? ? ?*/
? ? ? ? List<EurekaEndpoint> remainingHosts = new ArrayList<>(candidateHosts.size());
? ? ? ? for (EurekaEndpoint endpoint : candidateHosts) {
? ? ? ? ? ? if (!quarantineSet.contains(endpoint)) {
? ? ? ? ? ? ? ? remainingHosts.add(endpoint);
? ? ? ? ? ? }
? ? ? ? }
? ? ? ? candidateHosts = remainingHosts;
? ? }
? ? return candidateHosts;
}

final class PropertyBasedTransportConfigConstants {
? ? /**
? ? ?*省略部分源碼
? ? ?*/
? ? static class Values {
? ? ? ? static final int SESSION_RECONNECT_INTERVAL = 20*60;
? ? ? ? //默認(rèn)值為0.66
? ? ? ? static final double QUARANTINE_REFRESH_PERCENTAGE = 0.66;
? ? ? ? static final int DATA_STALENESS_TRHESHOLD = 5*60;
? ? ? ? static final int ASYNC_RESOLVER_REFRESH_INTERVAL = 5*60*1000;
? ? ? ? static final int ASYNC_RESOLVER_WARMUP_TIMEOUT = 5000;
? ? ? ? static final int ASYNC_EXECUTOR_THREADPOOL_SIZE = 5;
? ? }
}

/**
?*@return the percentage of the full endpoints set above which the ??
?*quarantine set is cleared in the range [0, 1.0]
?*/
double getRetryableClientQuarantineRefreshPercentage();

eureka.client.transport.retryableClientQuarantineRefreshPercentage = xxx

eureka.client.service-url.defaultZone=
http://localhost:8761/eureka,http://localhost:8762/eureka,http://localhost:8763/eureka,http://localhost:8764/eureka
eureka.client.transport.retryableClientQuarantineRefreshPercentage=1
eureka.client.service-url.defaultZone=
http://localhost:8761/eureka,http://localhost:8762/eureka,http://localhost:8763/eureka,http://localhost:8764/eureka
eureka.client.transport.retryableClientQuarantineRefreshPercentage=1