code: func (s *Restore) Registration(idx uint64, req *structs.RegisterRequest) error {
  	if err := s.store.ensureRegistrationTxn(s.tx, idx, req); err != nil {
  		return err
  	}
  	return nil
  }
docs: // Registration is used to make sure a node, service, and check registration is
  // performed within a single transaction to avoid race conditions on state
  // updates.