Gunicorn for production serving in Flask

Introduction

Gunicorn helps run your Flask app smoothly when many people use it at the same time. It makes your app ready for real-world use.

You want to make your Flask app available to many users at once.

You need a reliable way to run your app on a server.

You want better performance than the simple Flask development server.

You are preparing your app to be deployed on a cloud or VPS.

You want to handle multiple requests without crashing.

Syntax

Flask

gunicorn [OPTIONS] MODULE_NAME:APP_VARIABLE

MODULE_NAME is the Python file name without .py.

APP_VARIABLE is the Flask app object inside your module.

Examples

Runs the Flask app named app inside the app.py file with default settings.

Flask

gunicorn app:app

Runs with 4 worker processes and binds to all IPs on port 8000 for external access.

Flask

gunicorn -w 4 -b 0.0.0.0:8000 app:app

Runs and prints access logs to the console for easier debugging.

Flask

gunicorn --access-logfile '-' app:app

Sample Program

This simple Flask app returns a greeting. Running it with Gunicorn will serve it efficiently in production.

Flask

from flask import Flask

app = Flask(__name__)

@app.route('/')
def home():
    return 'Hello, Gunicorn!'

# To run this app with Gunicorn, save as app.py and run:
# gunicorn app:app

Important Notes

Gunicorn is not for Windows; use it on Linux or macOS servers.

Use multiple workers (-w) to handle more users smoothly.

Always test your app with Gunicorn before deploying live.

Summary

Gunicorn runs Flask apps efficiently for many users.

Use the command gunicorn module:app to start.

Configure workers and ports to fit your server needs.