Whoa, whoa, whoa. If you're building a serverless app, you don't start with Flask. You start with the lambda and plain old Python. Seriously, what he wrote basically said he tried to build to a construct which lambda isn't meant to directly support and then had all sorts of problems.
Stop trying to write a full server and then map it to lambda. Start with lambda and map it to your service. There, done. That's all you need to know.
Yep, the whole article looks like building a strawman against Python. This mentality of using "cool" frameworks and join the "cool" javascript kids (isn't that an oxymoron?) reeks of the hipsteresque mentality of the whole javascript community...just wait until the next `left_pad`.
Blame Zappa. It’s a very cool framework, but it promises serverless for frameworks including Django and Flask. It may be too leaky an abstraction for somebody trying to migrate an existing monolith to serverless or semi-serverless.
Stop trying to write a full server and then map it to lambda. Start with lambda and map it to your service. There, done. That's all you need to know.