'Update an existing stack with a new template.
Update an existing stack with a new template by patching the parameters
Add the flag patch to the args so the engine code can distinguish'

@util.identified_stack
def update_patch(self, req, identity, body):

    data = InstantiationData(body, patch=True)
    args = self.prepare_args(data)
    self.rpc_client.update_stack(req.context, identity, data.template(), data.environment(), data.files(), args, environment_files=data.environment_files())
    raise exc.HTTPAccepted()
