Nice approach for proxy. The challenge in both cases is to handle exceptions generated by faulty code. As you say in the article: the first argument of the callback is for error (including unhandled errors) and is not descriptive.

Different languages handle this differently. I have an article on this using Python with some code on GitHub. Here are the links to both if anyone is interested:

Integrating API Gateway — Lambda Responses

https://github.com/DanielEIlie/short-examples/tree/develop/APIG-Lambda