Deploying Python and Django Apps on Heroku
Last updated 15 November 2017
Table of Contents
- Django applications on Heroku
- Set up a virtual environment
- Declare app dependencies
- Specify the version of Python
- The Procfile
- Build your app and run it locally
- How to keep build artifacts out of git
- Deploy your application to Heroku
- One-off dynos
- Provision add-ons
- Running a worker
- Next steps
This article describes how to take an existing Python or Django app and deploy it to Heroku.
If you are new to Heroku, you might want to start with the Getting Started with Python on Heroku tutorial.
The best practices in this article assume that you have:
- an existing Python app
- Python installed locally. See the installation guides for OS X, Windows, and Linux
- Setuptools, Pip, and Virtualenv installed. See the Python install guides above for installation instructions
- a free Heroku account
- the Heroku CLI installed locally
The details of Heroku’s Python Support are described in the Heroku Python Support article.
Heroku will recognize a deployed application as a Python application only when the application has a
requirements.txt file in the root directory. Even if an application has no module dependencies, it should include an empty
requirements.txt file to document that your app has no dependencies.
Django applications on Heroku
Heroku supports all types of Python applications, including Django applications. The Configuring Django Apps for Heroku article describes this in detail and explains how to use the Heroku Django Starter Template which is strongly recommended for getting started with Django on Heroku.
Set up a virtual environment
virtualenv tool keeps the dependencies required by different projects isolated, by creating virtual environments for them. To use it, install virtualenv.
$ pip install virtualenv
In the top-level directory of your project, create a virtual environment for your project.
$ virtualenv venv
Next, activate the virtual environment. You must source the virtualenv environment for each terminal session where you run your app.
If you are using Windows, run this command.
If you are not using Windows, run this command.
$ source venv/bin/activate
While your virtual environment is active, all packages that you install using pip will be placed in your virtual environment.
Declare app dependencies
requirements.txt file lists the app dependencies together with their versions. When an app is deployed, Heroku reads this file and installs the appropriate Python dependencies.
To generate a
requirements.txt file, you can use the command
$ pip freeze > requirements.txt
Pip can also be used for advanced dependency management. See Python Dependencies via Pip to learn more.
Specify the version of Python
Optionally, you can specify the version of Python to use to run your application on Heroku. For more information, see Supported Python Runtimes.
A Procfile is a text file in the root directory of your application that defines process types and explicitly declares what command should be executed to start your app. Your
Procfile will look something like this:
web: gunicorn gettingstarted.wsgi --log-file -
This declares a single process type,
web, and the command needed to run it. The name,
web, is important here. It declares that this process type will be attached to the HTTP routing stack of Heroku, and receive web traffic when deployed.
The command in a web process type must bind to the port number specified in the
PORT environment variable. If it does not, the dyno will not start.
Build your app and run it locally
Run this command in your local directory to install the dependencies locally.
$ pip install -r requirements.txt Downloading/unpacking ... ... Successfully installed Django dj-database-url dj-static django-toolbelt gunicorn psycopg2 static3 Cleaning up...
Windows users may encounter an error when installing the dependencies locally. The production web server that we recommend, Gunicorn, does not work on Windows. To get your app running locally, use the default web server instead:
- Edit the
requirements.txtfile. Remove the line containing
gunicornand add another,
- Run pip again:
pip install -r requirements.txt- it should now work
- Edit the
Procfileso that your app will start using the default web server instead of Gunicorn. The contents of the file should read:
web: python manage.py runserver 0.0.0.0:$PORT
While this will get you up and running locally, please ensure you revert to Gunicorn when running in production.
To run your application locally, use the heroku local command, which was installed as part of the Heroku CLI:
$ heroku local web 11:48:19 web.1 | started with pid 36084 11:48:19 web.1 | 2014-07-17 11:48:19  [INFO] Starting gunicorn 19.0.0 11:48:19 web.1 | 2014-07-17 11:48:19  [INFO] Listening at: http://0.0.0.0:5000 (36084) 11:48:19 web.1 | 2014-07-17 11:48:19  [INFO] Using worker: sync 11:48:19 web.1 | 2014-07-17 11:48:19  [INFO] Booting worker with pid: 36087
Just like Heroku,
heroku local examines the
Procfile to determine what to run.
Your app should now be running on http://localhost:5000/.
How to keep build artifacts out of git
Prevent build artifacts from going into revision control by creating a
Here’s a typical
venv *.pyc staticfiles .env
Deploy your application to Heroku
After you commit your changes to git, you can deploy your app to Heroku.
$ git add . $ git commit -m "Added a Procfile." $ heroku login Enter your Heroku credentials. ... $ heroku create Creating intense-falls-9163... done, stack is cedar http://intense-falls-9163.herokuapp.com/ | firstname.lastname@example.org:intense-falls-9163.git Git remote heroku added $ git push heroku master ... -----> Python app detected ... -----> Launching... done, v7 https://intense-falls-9163.herokuapp.com/ deployed to Heroku
To open the app in your browser, type
Heroku allows you to run commands in a one-off dyno by using the
heroku run command. Use this for scripts and applications that only need to be executed when needed, such as maintenance tasks, loading fixtures into a database, or database migrations during application updates.
For debugging purposes, such as to examine the state of your application after a deploy, you can use
heroku run bash for a full shell into a one-off dyno. But remember that this will not connect you to one of the web dynos that may be running at the same time.
$ heroku run bash Running `bash` attached to terminal... up, run.2365 $ cat Procfile web: gunicorn gettingstarted.wsgi --log-file - $ exit exit
You can also use
heroku run to launch a Python shell attached to your local terminal for experimenting in your app’s environment. From there, you can import some of your application modules. Type
quit() to close the interactive shell.
$ heroku run python Running `python` attached to terminal... up, run.8826 Python 2.7.8 (default, Jul 15 2014, 15:37:51) [GCC 4.8.2] on linux2 Type "help", "copyright", "credits" or "license" for more information. >>> import os >>> quit()
Similarly, if you are using Django, you can use
heroku run to get a Django shell for executing arbitrary code against your deployed app:
$ heroku run python manage.py shell Running python manage.py shell attached to terminal... up, run.1 Python 2.7.6 (default, Jan 16 2014, 02:39:37) [GCC 4.4.3] on linux2 Type "help", "copyright", "credits" or "license" for more information. (InteractiveConsole) >>> from django.contrib.auth.models import User >>> User.objects.all() [<User: kenneth>]
You can also use the
heroku run command to sync the Django models with the database schema:
$ heroku run python manage.py syncdb Running python manage.py syncdb attached to terminal... up, run.1 Creating tables ... Creating table auth_permission Creating table auth_group_permissions Creating table auth_group Creating table auth_user_groups Creating table auth_user_user_permissions Creating table auth_user Creating table django_content_type Creating table django_session Creating table django_site You just installed Django's auth system, which means you don't have any superusers defined. Would you like to create one now? (yes/no): yes Username (leave blank to use 'u53976'): kenneth Email address: email@example.com Password: Password (again): Superuser created successfully. Installing custom SQL ... Installing indexes ... Installed 0 object(s) from 0 fixture(s)
Refer to the logging documentation for more general information about logging on Heroku.
The add-on marketplace has a large number of add-ons to choose from.
For Django applications, a Heroku Postgres
hobby-dev database is automatically provisioned. This populates the
DATABASE_URL environment variable.
No add-ons are automatically provisioned if a pure Python application is detected. If you need a SQL database for your app, add one explicitly:
$ heroku addons:create heroku-postgresql:hobby-dev
Running a worker
Procfile format lets you run any number of different process types. For example, if you added a worker process to complement your web process, your updated
Procfile will look something like this:
web: gunicorn gettingstarted.wsgi --log-file - worker: python worker.py
Running more than one dyno for an extended period may incur charges to your account. Read more about dyno-hour costs.
Push this change to Heroku, then launch a worker:
$ heroku ps:scale worker=1 Scaling worker processes... done, now running 1
heroku ps to see that your worker comes up, and
heroku logs to see your worker doing its work.