Eureka Client注册到Eureka Server的秘密

@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;
//用来保存所有Eureka Server信息(8761、8762、8763、8764)
List<EurekaEndpoint> candidateHosts = null;
//numberOfRetries的值代码写死默认为3次
for (int retry = 0; retry < numberOfRetries; retry++) {
	/**
	 *首次进入循环时，获取全量的Eureka Server信息(8761、8762、8763、8764)
	 */
	if (candidateHosts == null) {
        candidateHosts = getHostCandidates();
    }
	/**
	 *通过endpointIdx自增，依次获取Eureka Server信息，然后发送
	 *注册的Post请求.
	 */
    currentEndpoint = candidateHosts.get(endpointIdx++);
    currentHttpClient = clientFactory.newClient(currentEndpoint);
    try {
       /**
	 	*发送注册的Post请求动作，注意如果成功，则跳出循环，如果失败则
	 	*根据endpointIdx依次获取下一个Eureka Server.
	 	*/
        response = requestExecutor.execute(currentHttpClient);
        return respones;
    } catch (Exception e) {
        //向注册中心(Eureka Server)发起注册的post出现异常时，打印日志...
    }
    //如果此次注册动作失败，将当前的信息保存到quarantineSet中(一个Set集合)
    if (currentEndpoint != null) {
        quarantineSet.add(currentEndpoint);
    }
}
//如果都失败,则以异常形式抛出...
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() {
    /**
     * 获取所有defaultZone配置的注册中心信息(Eureka Server)，
     * 在本文例子中代表4个(8761、8762、8763、8764)Eureka Server
     */
    List candidateHosts = clusterResolver.getClusterEndpoints();
    /**
     * quarantineSet这个Set集合中保存的是不可用的Eureka Server
     * 此处是拿不可用的Eureka Server与全量的Eureka Server取交集
     */
    quarantineSet.retainAll(candidateHosts);
    /**
     * 根据RetryableClientQuarantineRefreshPercentage参数计算阈值
     * 该阈值后续会和quarantineSet中保存的不可用的Eureka Server个数
     * 作比较，从而判断是否返回全量的Eureka Server还是过滤掉不可用的
     * Eureka Server。
     */
    int threshold = 
       (int) (
        candidateHosts.size()
              *
        transportConfig.getRetryableClientQuarantineRefreshPercentage()
        );
    if (quarantineSet.isEmpty()) {
        /**
         * 首次进入的时候，此时quarantineSet为空，直接返回全量的
         * Eureka Server列表
         */
    } else if (quarantineSet.size() >= threshold) {
        /**
         * 将不可用的Eureka Server与threshold值相比较，如果不可
         * 用的Eureka Server个数大于阈值，则将之间保存的Eureka
         * Server内容直接清空，并返回全量的Eureka Server列表。
         */
        quarantineSet.clear();
    } else {
        /**
         * 通过quarantineSet集合保存不可用的Eureka Server来过滤
         * 全量的EurekaServer，从而获取此次Eureka Client要注册要
         * 注册的Eureka Server实例地址。
         */
        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 {
	/**
	 *省略部分源码
	 */
    static class Values {
        static final int SESSION_RECONNECT_INTERVAL = 20*60;
        //默认值为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();

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());
    
    /**
     * 增加判断如果threshold的值过大，即超过Eureka Server
     * 列表的数量，那么将其再次赋值，赋值的内容为Eureka Server
     * 列表的数量。
     */
    if (threshold > candidateHosts.size()) {
  	    threshold = candidateHosts.size();
    }

    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;
}