Gunicorn vs Uvicorn in FastAPI

What is Uvicorn?

Uvicorn is an ASGI server used to run FastAPI applications. It is commonly used during development and can also be used in production.

Example: uvicorn main:app --reload

Sample Code:

import uvicorn
from fastapi import FastAPI

app = FastAPI()

@app.get("/")
async def index():
return {"message": "Hello World!"}

output : message: Hello World!

What is Gunicorn?

Gunicorn is a Python application server that manages multiple worker processes. It is commonly used for production deployments.

Gunicorn itself is traditionally a WSGI server, so for FastAPI it is used together with an ASGI worker such as Uvicorn's worker implementation.

sample code:

import uvicorn
from fastapi import FastAPI

app = FastAPI()

@app.get("/")
async def index():
return {"message": "Hello World"}

Run the command in Terminal

gunicorn main:app --reload --log-level info --workers 3 --bind 0.0.0.0:8000

output: 

Gunicorn works on linux or docker os systems, in windows it might not work.

Message: Hello World!!!!

What is WSGI?

WSGI (Web Server Gateway Interface) is a standard that allows a Python web application to communicate with a web server. It is mainly designed for synchronous applications such as traditional Flask and Django applications.

What is ASGI?

ASGI (Asynchronous Server Gateway Interface) is a newer standard that allows Python web applications to handle both synchronous and asynchronous operations. FastAPI is built for ASGI.