code: func RunPS(dockerCli *KubeCli, options options.PS) error {
  	filters := options.Filter.Value()
  	if err := filters.Validate(supportedPSFilters); err != nil {
  		return err
  	}
  	client, err := dockerCli.composeClient()
  	if err != nil {
  		return err
  	}
  	stacks, err := client.Stacks(false)
  	if err != nil {
  		return err
  	}
  	stackName := options.Namespace
  	_, err = stacks.Get(stackName)
  	if apierrs.IsNotFound(err) {
  		return fmt.Errorf("nothing found in stack: %s", stackName)
  	}
  	if err != nil {
  		return err
  	}
  	pods, err := fetchPods(stackName, client.Pods(), filters)
  	if err != nil {
  		return err
  	}
  	if len(pods) == 0 {
  		return fmt.Errorf("nothing found in stack: %s", stackName)
  	}
  	return printTasks(dockerCli, options, stackName, client, pods)
  }
docs: // RunPS is the kubernetes implementation of docker stack ps