code: def _initialize_metadata_service(cls):
          
          if cls.inited:
              return
  
          instance_id = cls.get_attribute('instance/id')
  
          if instance_id is not None:
              cls.is_running = True
  
              _GCP_METADATA_MAP['instance_id'] = instance_id
  
              # fetch attributes from metadata request
              for attribute_key, attribute_uri in _GCE_ATTRIBUTES.items():
                  if attribute_key not in _GCP_METADATA_MAP:
                      attribute_value = cls.get_attribute(attribute_uri)
                      if attribute_value is not None:  # pragma: NO COVER
                          _GCP_METADATA_MAP[attribute_key] = attribute_value
  
          cls.inited = True
docs: Initialize metadata service once and load gcp metadata into map
          This method should only be called once.