EurekaServer端接收请求

• EurekaServer端接收续约(心跳)请求的方法是eureka-core包里的InstanceResource-renewLease方法，这个方法同EurekaServer接收注册信息的方法一样，都用isReplication这个字段来表明当前请求是接收EurekaClient端发来的续约(心跳)请求还是其他EurekaServer端发来的同步信息的请求。debug发现续约时isReplication还是为null
  具体代码如下：

  // 接收EurekaClient端发送的续租(心跳)请求
  // 也有可能是接收其他EurekaServer端同步数据的请求
  @PUT
  public Response renewLease(// 是否是Replication模式
          @HeaderParam(PeerEurekaNode.HEADER_REPLICATION) String isReplication,
          @QueryParam("overriddenstatus") String overriddenStatus,// 实例的覆盖状态
          @QueryParam("status") String status,// 实例状态
          // 实例信息在EurekClient端上次被修改的时间
          @QueryParam("lastDirtyTimestamp") String lastDirtyTimestamp) {
      boolean isFromReplicaNode = "true".equals(isReplication);
      // 续租(心跳)
      boolean isSuccess = registry.renew(app.getName(), id, isFromReplicaNode);
  
      // Not found in the registry, immediately ask for a register
      // 续租失败，返回404，EurekaClient端收到404后会发起注册请求
      if (!isSuccess) {
          logger.warn("Not Found (Renew): {} - {}", app.getName(), id);
          return Response.status(Status.NOT_FOUND).build();
      }
      // Check if we need to sync based on dirty time stamp, the client
      // instance might have changed some value
      Response response = null;
      if (lastDirtyTimestamp != null && serverConfig.shouldSyncWhenTimestampDiffers()) {
          // 验证传入的lastDirtyTimestamp和EurekaServer端保存的lastDirtyTimestamp是否相同
          response = this.validateDirtyTimestamp(Long.valueOf(lastDirtyTimestamp), isFromReplicaNode);
          // Store the overridden status since the validation found out the node that replicates wins
          if (response.getStatus() == Response.Status.NOT_FOUND.getStatusCode()
                  && (overriddenStatus != null)
                  && !(InstanceStatus.UNKNOWN.name().equals(overriddenStatus))
                  && isFromReplicaNode) {
              registry.storeOverriddenStatusIfRequired(app.getAppName(), id, InstanceStatus.valueOf(overriddenStatus));
          }
      } else {
          // 续约成功，返回200
          response = Response.ok().build();
      }
      logger.debug("Found (Renew): {} - {}; reply status={}", app.getName(), id, response.getStatus());
      return response;
  }

• 在boolean isSuccess = registry.renew(app.getName(), id, isFromReplicaNode);这里调用了PeerAwareInstanceRegistryImpl的renew(appName, id, isReplication)方法，代码如下：

  public boolean renew(final String appName, final String id, final boolean isReplication) {
      // 调用父类里的renew(appName, id, isReplication)方法续约
      if (super.renew(appName, id, isReplication)) {
          // 如果是续约请求则向其他EurekaServer节点同步续约信息
          // 如果是同步信息请求则直接返回
          replicateToPeers(Action.Heartbeat, appName, id, null, null, isReplication);
          return true;
      }
      return false;
  }

• AbstractInstanceRegistry的renew(appName, id, isReplication)方法代码如下：

  public boolean renew(String appName, String id, boolean isReplication) {
      RENEW.increment(isReplication);
      // 根据实例名称取出实例信息集合
      Map<String, Lease<InstanceInfo>> gMap = registry.get(appName);
      Lease<InstanceInfo> leaseToRenew = null;
      if (gMap != null) {
          // 根据实例id取出具体实例租约信息
          leaseToRenew = gMap.get(id);
      }
      // 租约不存在
      if (leaseToRenew == null) {
          RENEW_NOT_FOUND.increment(isReplication);
          logger.warn("DS: Registry: lease doesn't exist, registering resource: {} - {}", appName, id);
          return false;
      } else {
          InstanceInfo instanceInfo = leaseToRenew.getHolder();
          if (instanceInfo != null) {
          // touchASGCache(instanceInfo.getASGName());
              // 获得实例的覆盖状态
              InstanceStatus overriddenInstanceStatus = this.getOverriddenInstanceStatus(
                      instanceInfo, leaseToRenew, isReplication);
              // 实例覆盖状态为UNKNOWN，续租失败
              if (overriddenInstanceStatus == InstanceStatus.UNKNOWN) {
                  logger.info("Instance status UNKNOWN possibly due to deleted override for instance {}"
                          + "; re-register required", instanceInfo.getId());
                  RENEW_NOT_FOUND.increment(isReplication);
                  return false;
              }
              // 实例状态与覆盖状态不一致
              if (!instanceInfo.getStatus().equals(overriddenInstanceStatus)) {
                  logger.info(
                          "The instance status {} is different from overridden instance status {} for instance {}. "
                                  + "Hence setting the status to overridden status", instanceInfo.getStatus().name(),
                                  instanceInfo.getOverriddenStatus().name(),
                                  instanceInfo.getId());
                  // 强行把实例的覆盖状态设为实例状态
                  // 即status = overriddenInstanceStatus
                  instanceInfo.setStatusWithoutDirty(overriddenInstanceStatus);
              }
          }
          renewsLastMin.increment();
          // 续租(设置lastUpdateTimestamp(租约最后更新时间))
          leaseToRenew.renew();
          return true;
      }
  }