Gunicorn Local Python Web Development Guide

Gunicorn (Green Unicorn) is a Python WSGI HTTP server commonly used with Nginx in production environments. It can be used to simulate production deployment locally when developing with Django or Flask.

Default localhost Access

By default, it listens on port 8000, accessible only from the local machine (127.0.0.1).

Installation and Running

pip install gunicorn

Flask Example

gunicorn -w 4 -b 127.0.0.1:8000 app:app

Django Example

gunicorn myproject.wsgi:application -b localhost:8000

-w 4 indicates 4 worker processes.

Development Comparison

For daily development, Django/Flask typically use the built-in server:

python manage.py runserver    # Django → http://localhost:8000
flask run                     # Flask → http://localhost:5000

Gunicorn is suitable for local stress testing before deployment or for debugging with Nginx.

Binding Ports

gunicorn -b 0.0.0.0:8080 app:app

This allows access from the local area network; the local machine still uses http://localhost:8080.

Common Issues

ModuleNotFoundError
Ensure the virtual environment is activated and the app:app module path is correct.

Address already in use
Change the -b port or terminate the process occupying port 8000.

Summary

Gunicorn defaults to http://localhost:8000 for production-level local running of Python WSGI applications.