def update_node(self, node, diff=None):
        """Updates the node's attributes."""
        lb = node.parent
        if not lb:
            raise exc.UnattachedNode("No parent Load Balancer for this node "
                    "could be determined.")
        if diff is None:
            diff = node._diff()
        req_body = {"node": diff}
        resp, body = self.api.method_put("/loadbalancers/%s/nodes/%s" %
                (lb.id, node.id), body=req_body)
        return resp, body
Updates the node's attributes.