Returns a Node instance.

        :param node_id: Node identifier

        :returns: Node instance

def get_node(self, node_id):
        """
        Returns a Node instance.

        :param node_id: Node identifier

        :returns: Node instance
        """

        try:
            UUID(node_id, version=4)
        except ValueError:
            raise aiohttp.web.HTTPBadRequest(text="Node ID {} is not a valid UUID".format(node_id))

        for node in self._nodes:
            if node.id == node_id:
                return node

        raise aiohttp.web.HTTPNotFound(text="Node ID {} doesn't exist".format(node_id))