Configuring Django Apps for Heroku

Last updated 09 February 2016

Heroku supports all types of Python applications, including Django applications. However, Django’s complex configuration patterns can make life a little difficult for cutting-edge developers.

This best-practice guide outlines all Django-specific requirements for deploying Python applications on Heroku.

Creating a new Django project

When starting a brand new Django project, you can use the official Heroku Django Starter Template to get started immediately. This template includes all best-practices and recommendations outlined in this article, and is strongly recommended for getting started with Django on Heroku.

Assuming you already have Django installed, you can create a new pre-configured Django project with the following command:

$ django-admin startproject --template=https://github.com/heroku/heroku-django-template/archive/master.zip --name=Procfile  myproject

That’s it! This will give you a brand new, fresh Django application that will “just work” on Heroku.

Migrating an existing Django project

You may want to migrate an existing Django project. Let’s go through all of the components included in the starter template mentioned above.

The basics

First, and most importantly, Heroku web applications require a Procfile.

This file (named Procfile) is used to explicitly declare your application’s process types and entry points. It is located in the root of your repository.

Procfile

web: gunicorn myproject.wsgi --log-file -

This Procfile requires Gunicorn, the production web server that we recommend for Django applications. For more information, see Deploying Python Applications with Gunicorn.

Installing gunicorn

$ pip install gunicorn
...
$ pip freeze > requirements.txt

Database configuration

On Heroku, sensitive credentials are stored in the environment as config vars. This includes database connection information (named DATABASE_URL), which is traditionally hardcoded in Django applications.

The dj-database-url package parses the DATABASE_URL environment variable and converts it to Django’s desired configuration format, automatically.

Installing dj-database-url

$ pip install dj-database-url
...
$ pip freeze > requirements.txt

settings.py

# Update database configuration with $DATABASE_URL.
import dj_database_url
db_from_env = dj_database_url.config()
DATABASES['default'].update(db_from_env)

Database connection persistence

By default, Django will only create a new persistent database connection for every request cycle of your application. This is a very expensive operation, and can slow down your Django application.

Luckily, Django provides persistent connections, which are a great way to improve the performance of your Django application.

settings.py

# Update database configuration with $DATABASE_URL.
import dj_database_url
db_from_env = dj_database_url.config(conn_max_age=500)
DATABASES['default'].update(db_from_env)

For more information, see Concurrency and Database Connections in Django.

Static assets and file serving

Django settings for static assets can be a bit difficult to configure and debug. However, if you just add the following settings to your settings.py, everything should work exactly as expected:

settings.py

# Static files (CSS, JavaScript, Images)
# https://docs.djangoproject.com/en/1.9/howto/static-files/

PROJECT_ROOT = os.path.dirname(os.path.abspath(__file__))

STATIC_ROOT = os.path.join(PROJECT_ROOT, 'staticfiles')
STATIC_URL = '/static/'

# Extra places for collectstatic to find static files.
STATICFILES_DIRS = (
    os.path.join(PROJECT_ROOT, 'static'),
)

Older versions of Django won’t automatically create the target directory (STATIC_ROOT) that collectstatic uses, if it isn’t available. You may need to create this directory in your codebase, so it will be available when collectstatic is run. Git does not support empty file directories, so you will have to create a file inside that directory as well.

For more information, see Django and Static Assets.

Whitenoise

By default, Django does not support serving static files in production. We recommend using the WhiteNoise project for best-practice serving of static assets in production.

Installing Whitenoise

$ pip install whitenoise
...
$ pip freeze > requirements.txt

settings.py

# Simplified static file serving.
# https://warehouse.python.org/project/whitenoise/

STATICFILES_STORAGE = 'whitenoise.django.GzipManifestStaticFilesStorage'

wsgi.py

from django.core.wsgi import get_wsgi_application
from whitenoise.django import DjangoWhiteNoise

application = get_wsgi_application()
application = DjangoWhiteNoise(application)

That’s it! See the WhiteNoise documentation for more details.

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