Uvicorn server basics in FastAPI

Introduction

Uvicorn runs your FastAPI app so people can use it through the internet. It listens for requests and sends back responses.

You want to test your FastAPI app locally on your computer.

You need to run your FastAPI app on a server for others to access.

You want to see your API working in a browser or with tools like Postman.

You are developing and want to reload the server automatically when code changes.

Syntax

FastAPI

uvicorn module_name:app --host 0.0.0.0 --port 8000 --reload

module_name:app means the Python file and the FastAPI app object inside it.

--reload restarts the server when you change code, useful for development.

Examples

Runs the app in main.py on default host 127.0.0.1 and port 8000.

FastAPI

uvicorn main:app

Makes the app available on all network interfaces at port 5000.

FastAPI

uvicorn main:app --host 0.0.0.0 --port 5000

Runs with auto-reload so changes in code restart the server automatically.

FastAPI

uvicorn main:app --reload

Sample Program

This simple FastAPI app returns a greeting message at the root URL. Run it with Uvicorn to see it in action.

FastAPI

from fastapi import FastAPI

app = FastAPI()

@app.get('/')
async def read_root():
    return {"message": "Hello from FastAPI!"}

# To run this app, save as main.py and run:
# uvicorn main:app --reload

Important Notes

Use --reload only in development, not in production.

Uvicorn is fast and supports async code, making your API responsive.

Check the terminal for server logs and errors when running Uvicorn.

Summary

Uvicorn runs your FastAPI app so it can handle web requests.

You specify the app location and options like host, port, and reload.

Use uvicorn module_name:app --reload to develop easily.