  void addCompletionCallback() {
    health_checker_->addHostCheckCompleteCb(
        [this](HostSharedPtr host, HealthTransition changed_state) -> void {
          onHostStatus(host, changed_state);
        });
  }
  void addCompletionCallback() {
    health_checker_->addHostCheckCompleteCb(
        [this](HostSharedPtr host, HealthTransition changed_state) -> void {
          onHostStatus(host, changed_state);
        });
  }