Please don't make complex projects on Lambdas.

No, seriously. I've been talking about it for some time, but here we go again: If your project requires substantial codebase, test coverage, complexity + expected to live for over a year - I would skip Lambdas (or any other serverless-tightened approach) 100%. The main reason is being dependant on framework. Why should I create loads of configurations (aka serverless.yaml) + tons of handlers to make sure the logic works? Bottom line is to have a Dockerfile and that's it - nothing really touches the code execution context. With Lambdas it is also about the testability - if there is a "brownfield" project created on lambdas without any test - you will have to spend ages creating lots of mocks as well as any attempts for integration testing. Whatever you do most of the things will break on your next `sls deploy` - guaranteed. And what if Serverless gets totally deprecated one day? Your codebase is so tightened/glued to it that initial intention to simplify the flow will ruin any future feasibility and convert itself into a giant pile of technical debt.

Lambdas should be used for Slack Bot notifications at max.