5. Uvicorn Basics

What is Uvicorn?

Uvicorn is an ASGI (Asynchronous Server Gateway Interface) server for Python. It's the recommended server for running FastAPI applications.

Common Options

# Basic usage
uvicorn main:app --reload

# Custom host and port
uvicorn main:app --host 0.0.0.0 --port 8080

# Number of workers (production)
uvicorn main:app --workers 4

# Log level
uvicorn main:app --log-level debug

# SSL
uvicorn main:app --ssl-keyfile key.pem --ssl-certfile cert.pem

Programmatic Startup

# run.py
import uvicorn

if __name__ == "__main__":
    uvicorn.run(
        "main:app",
        host="0.0.0.0",
        port=8000,
        reload=True,
        log_level="info"
    )

Lifecycle Events

Uvicorn fires startup and shutdown events:

@app.on_event("startup")
async def startup():
    print("Server is starting...")

@app.on_event("shutdown")
async def shutdown():
    print("Server is shutting down...")