def create_bucket(self, instance, bucket_name):
        """
        Create a new bucket in the specified instance.

        :param str instance: A Yamcs instance name.
        :param str bucket_name: The name of the bucket.
        """
        req = rest_pb2.CreateBucketRequest()
        req.name = bucket_name
        url = '/buckets/{}'.format(instance)
        self._client.post_proto(url, data=req.SerializeToString())