docs: def cname(cls, map_name, container, instance=None):
          """
          Generates a container name that should be used for creating new containers and checking the status of existing
          containers.
  
          In this implementation, the format will be ``<map name>.<container name>.<instance>``. If no instance is
          provided, it is just ``<map name>.<container name>``.
  
          :param map_name: Container map name.
          :type map_name: unicode | str
          :param container: Container configuration name.
          :type container: unicode | str
          :param instance: Instance name (optional).
          :type instance: unicode | str
          :return: Container name.
          :rtype: unicode | str
          """
          if instance:
              return '{0}.{1}.{2}'.format(map_name, container, instance)
          return '{0}.{1}'.format(map_name, container)