I’ve been running essential production systems with pythons uvicorn and 1 worker reliably, mainly because I get to use global state and the performance is more than fine. It’s much better than having to store global state somewhere else. Just make sure you measure the usage and chose a different design when you notice when this becomes a problem.

I have inherited a suite of apps that do this. I have mixed feelings about this: on the one hand, many of them work just fine and will never need a second worker, and they were relatively easy for inexperienced devs to put together.

On the other hand, some of them do have performance problems and are a nightmare to migrate to a different solution, it's hard to reason about what parts of the application turn out to be stateful.