The update_function_configuration currently returns an empty dict no matter what but certain lambda libraries (ie, Zappa) require a realistic return value... which is simply the current config after being updated.

https://github.com/localstack/localstack/blob/9cba1010dfcbf2b7672df4d7da46b7e8ab287f64/localstack/services/awslambda/lambda_api.py#L872

https://boto3.amazonaws.com/v1/documentation/api/latest/reference/services/lambda.html#Lambda.Client.update_function_configuration

There might also be some other magic enriching that result but my quick read-through looks like it's an empty dict.



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func_arn = lambda_api.func_arn(func_name)
        
        executor.destroy_existing_docker_containers()
        self.assertEqual(len(executor.get_all_container_names()), 0)
        
        zip_file = testutil.create_lambda_archive(
            load_file(TEST_LAMBDA_ENV),
            get_content=True,
            libs=TEST_LAMBDA_LIBS,
            runtime=LAMBDA_RUNTIME_PYTHON27
        )
        testutil.create_lambda_function(
            func_name=func_name,
            zip_file=zip_file,
            runtime=LAMBDA_RUNTIME_PYTHON27,
            envvars={'Hello': 'World'}
        )
        self.assertEqual(len(executor.get_all_container_names()), 0)
        self.lambda_client.invoke(FunctionName=func_name, Payload=b'{}')
        self.assertEqual(len(executor.get_all_container_names()), 1)
        
        executor.idle_container_destroyer()
        self.assertEqual(len(executor.get_all_container_names()), 1)
        
        executor.function_invoke_times[func_arn] = time.time() - lambda_executors.MAX_CONTAINER_IDLE_TIME_MS
        executor.idle_container_destroyer()
        self.assertEqual(len(executor.get_all_container_names()), 0)
        
        testutil.delete_lambda_function(func_name)