code: func (b *Backend) TriggerChord(groupUUID string) (bool, error) {
  	query := bson.M{
  		"_id":             groupUUID,
  		"chord_triggered": false,
  	}
  	change := bson.M{
  		"$set": bson.M{
  			"chord_triggered": true,
  		},
  	}
  
  	_, err := b.groupMetasCollection.UpdateOne(context.Background(), query, change, options.Update())
  
  	if err != nil {
  		if err == mongo.ErrNoDocuments {
  			log.WARNING.Printf("Chord already triggered for group %s", groupUUID)
  			return false, nil
  		}
  		return false, err
  	}
  	return true, nil
  }
docs: // TriggerChord flags chord as triggered in the backend storage to make sure
  // chord is never triggered multiple times. Returns a boolean flag to indicate
  // whether the worker should trigger chord (true) or no if it has been triggered
  // already (false)