code: func nodeMatches(s *api.Service, n *api.Node) bool {
  	if n == nil {
  		return false
  	}
  
  	constraints, _ := constraint.Parse(s.Spec.Task.Placement.Constraints)
  	return constraint.NodeMatches(constraints, n)
  }
docs: // Checks if the current assigned node matches the Placement.Constraints
  // specified in the task spec for Updater.newService.