def connect_resource(self):
        """
        Connect to an AWS API via boto3 high-level resource connection and set
        ``self.resource_conn`` to the `boto3.resource <https://boto3.readthed
        ocs.org/en/latest/reference/core/boto3.html#boto3.resource>`_ object
        (a ``boto3.resources.factory.*.ServiceResource`` instance).
        If ``self.resource_conn`` is not None,
        do nothing. This connects to the API name given by ``self.api_name``.

        :returns: None
        """
        if self.resource_conn is not None:
            return
        kwargs = self._boto3_connection_kwargs
        self.resource_conn = boto3.resource(self.api_name, **kwargs)
        logger.info("Connected to %s (resource) in region %s", self.api_name,
                    self.resource_conn.meta.client._client_config.region_name)