apollo-biz/src/main/java/com/ctrip/framework/apollo/biz/service/InstanceService.java/InstanceService/findInstance
class InstanceService:  public Instance findInstance(String appId, String clusterName, String dataCenter, String ip) {
    return instanceRepository.findByAppIdAndClusterNameAndDataCenterAndIp(appId, clusterName,
        dataCenter, ip);
  }