docs: def get_instance_subnet_name(self, instance):
          """
          Return a human readable name for given instance's subnet, or None.
  
          Uses stored config mapping of subnet IDs to names.
          """
          # TODO: we have to do this here since we are monkeypatching Instance.
          # If we switch to custom Instance (sub)class then we could do it in the
          # object, provided it has access to the configuration data.
          if instance.subnet_id:
              # Account for omitted 'subnet-'
              subnet = self.config['subnets'][instance.subnet_id[7:]]
          else:
              subnet = BLANK
          return subnet