def get_index_name(app_id, namespace, name):
  """ Gets the internal index name.

  Args:
    app_id: A str, the application identifier.
    namespace: A str, the application namespace.
    name: A str, the index name.
  Returns:
    A str, the internal name of the index.
  """
  return '{}_{}_{}'.format(app_id, namespace, name)