$ gunicorn project.wsgi:application

# mysite/settings/set_env.py

import os

_environment = os.getenv('environment', None)
if _environment == "production":
    os.environ.setdefault("DJANGO_SETTINGS_MODULE", "mysite.settings.production")
elif _environment == "development":
    os.environ.setdefault("DJANGO_SETTINGS_MODULE", "mysite.settings.development")
else:
    os.environ.setdefault("DJANGO_SETTINGS_MODULE", "mysite.settings.local")