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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data = json.loads(to_str(request.data))
    iam_client = aws_stack.connect_to_service('iam')
    sid = short_uid()
    policy = {
        'Version': IAM_POLICY_VERSION,
        'Id': 'LambdaFuncAccess-%s' % sid,
        'Statement': [{
            'Sid': sid,
            'Effect': 'Allow',
            
            
            'Action': data.get('Action'),
            'Resource': func_arn(function)