code: func (s *APIServer) upsertNodes(auth ClientI, w http.ResponseWriter, r *http.Request, p httprouter.Params, version string) (interface{}, error) {
  	var req upsertNodesReq
  	if err := httplib.ReadJSON(r, &req); err != nil {
  		return nil, trace.Wrap(err)
  	}
  	if !services.IsValidNamespace(req.Namespace) {
  		return nil, trace.BadParameter("invalid namespace %q", req.Namespace)
  	}
  
  	nodes, err := services.GetServerMarshaler().UnmarshalServers(req.Nodes)
  	if err != nil {
  		return nil, trace.Wrap(err)
  	}
  
  	err = auth.UpsertNodes(req.Namespace, nodes)
  	if err != nil {
  		return nil, trace.Wrap(err)
  	}
  
  	return message("ok"), nil
  }
docs: // upsertNodes is used to bulk insert nodes into the backend.