Comment by gtd

> It is bad practice to have your authentication database be the same as your app database.

No, this is resume-driven-development, Google-scale-wannabe FUD. Understand your requirements. Multiple databases is non-trivial overhead. The only reason to add multiple databases is if you need scale that can't be handled via simple caching.

Of course it's hard to anticipate what level of scale you'll have later, but I can tell you this: for every tiny startup that successfully anticipated their scaling requirements and built a brilliant microservices architecture that proactively paved the way to their success, there's a 100 burnt out husks of companies that never found product market fit because the engineering team was too busy fantasizing about "web-scale" and padding their resume by overengineering every tiny and unused feature they built.

If you want to get a job at FAANG and suckle at the teat of megacorporations who's trajectory was all based on work done in the early 2000s, by all means study up on "best practices" to recite at your system design interview. On the other hand, if you want to build the next great startup, you need to lose the big co mentality and start thinking critically from first principles about power to weight ratio and YAGNI.