What is Uvicorn and how is it used with FastAPI?
Answer
Uvicorn is a lightning-fast ASGI server for Python, based on uvloop and httptools. It is the standard server for running FastAPI in production. Development: uvicorn main:app --reload --port 8000 — --reload restarts on code changes. Production: uvicorn main:app --host 0.0.0.0 --port 8000 --workers 4. For multi-process production deployments, use Gunicorn with Uvicorn workers: gunicorn main:app -w 4 -k uvicorn.workers.UvicornWorker. Gunicorn manages multiple worker processes for resilience; each worker runs Uvicorn's ASGI server. Alternatively, use uvicorn --workers 4 (Uvicorn's built-in multi-process mode). With async FastAPI, a single worker handles many concurrent requests, so you need fewer workers than with synchronous WSGI (typically 1-2 per CPU core instead of 4-8).