Move from Flask to FastAPI for the API

[Venefilyn]

Description

Since we only make use of Flask for the API we consider using something that is built for API development. I propose using something like FastAPI for two reasons:

• Larger community that seems to be more long-term sustainable than Flask and its plugins
• Gets us closer to something built for async rather than patched in later

There are some huge changes that would need to be addressed

• FastAPI is using Pydantic for their models and data validation, which can be paired with SQLAlchemy using SQLModel
• FastAPI is primarily an ASGI app, compared to Flask which is WSGI
• Figure out how to handle API versioning and what actual implementation differences there would be to change

However there is an option that we can utilize to have a gradual move

• We can for now hardcode WSGI and mount Flask as a middleware for a specific endpoint (i.e. keep Flask running on /api/ and running FastAPI on /api/v1 and /api/nightly/ or something similar

Benefit

• Faster API application with currently easier future maintainability
• Async support
• Different routers for different versions (e.g. /api/v1 /api/v2, /api/latest)

Importance

Medium-High importance

Gives us two main impactful things that is otherwise difficult to handle in the current server and API

1. Documented endpoints with a greater flexibility on how endpoint data is structured, which gives us a chance to avoid modifying requests like we currently do and instead put that into the model
2. Async and WebSockets -- Currently this is difficult to do in Flask and with WebSockets not being a first-class citizen it becomes a weird way to write WebSocket support

As well as forcing us to make good API decisions regarding versioning, and proper pagination structure

What is the impacted category (job)?

General

Workaround

• There is an existing workaround that can be used until this feature is implemented.

Participation

• I am willing to submit a pull request for this issue. (Packit team is happy to help!)