Fast API – Gunicorn vs Uvicorn

In this article, we will explore Gunicorn and Uvicorn in the context of FastAPI applications, examining two integral components essential for the deployment and execution of Python web services.

What is FastAPI?

FastAPI is a modern web framework specifically crafted for Python 3.8 and newer versions, leveraging standard Python-type hints for API creation. It is constructed upon the robust bases of Starlette and Pydantic, offering a range of notable advantages. The key features of FastAPI include:

• Very high performance.
• Faster to code.
• Fewer bugs.
• Easier to learn and use.
• Takes less time to read the docs.

What is Uvicorn?

Uvicorn is the recommended lightweight ASGI server for FastAPI, optimized for asynchronous programming. Known for its exceptional performance in handling asynchronous code, it’s favored by FastAPI users for its user-friendly design suitable for both development and production environments. Uvicorn also offers a convenient –reload option, automatically restarting the server upon detecting code changes, proving particularly valuable in the development phase.

Example:

Python3

import uvicorn
from fastapi import FastAPI

app = FastAPI()

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

run the below command in terminal

uvicorn main:app --reload

Output:

Message: Hello World!!!!

What is Gunicorn ?

Gunicorn, a WSGI server, can be used alongside Uvicorn to serve FastAPI applications, despite not being specifically designed for ASGI. Commonly paired with frameworks like Flask and Django, Gunicorn boasts a mature ecosystem and is favored for production deployments. However, its synchronous nature, processing one request at a time per worker process, necessitates combining it with Uvicorn for optimal utilization of asynchronous programming in FastAPI.

Example:

Python3

import uvicorn
from fastapi import FastAPI

app = FastAPI()

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

run the below command

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

Output:

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

Message: Hello World!!!!

Difference between Gunicorn vs Uvicorn

Here are the differences based on some features between uvicorn and Gunicorn.

Features	Uvicorn	Gunicorn
Server Type	ASGI (Asynchronous Server Gateway Interface)	WSGI (Web Server Gateway Interface)
Suitable For	Asynchronous web applications (AsyncIO)	Synchronous web applications (Flask, Django)
Development	Often used during development and testing	Typically used in production deployments
Auto-reload	Can auto-reload application on code changes	Not designed for auto-reloading in development
Concurrency	Single-process server by default	Can spawn multiple worker processes
Production Use	Not ideal for high-traffic production	Designed for production with multiple workers
Frameworks	FastAPI, Starlette, etc.	Flask, Django, Pyramid, etc.
Deployment	May require a reverse proxy in production	Suitable for directly serving web applications
Scalability	Limited in handling concurrent connections	Efficient at handling a large number of connections
Adaptability	Can run WSGI applications with adapter	Designed specifically for WSGI applications