Deploying a Python Flask App to Heroku

This article guides you through the steps to deploy a fresh Python Flask app to Heroku. I am a Mac user and my IDE of choice is PyCharm, but you can adapt this tutorial to your own environment easily.

Source code of this sample project is available on GitHub.

Initial setup

First, register a new account on www.heroku.com .

Download & install the command line tools at https://devcenter.heroku.com/articles/getting-started-with-python#set-up . Enter terminal and enter the command: 

heroku login

Your credentials will be asked. Enter them, and you’ll be in contact with Heroku.

New project

Define a new Flask project in PyCharm. I will call it Helloku2 . When you run the app locally, you should be seeing a web page.

To prepare your app for live usage, we need a real web server. Add gunicorn to your project. In the terminal, ensure you can start the app by typing:

gunicorn app:app

The application should be accessible in your browser. You can terminate the application with CTRL+C.

Prepare project for Heroku

Create a new file called Procfile (no extension) in the root of your application, which contains one line:

web gunicorn app:app

This will tell Heroku that this is a web application, and start it with gunicorn (like in the terminal).

Go to the terminal and type:

pip freeze > requirements.txt

This command will put all of your dependencies into a file called requirements.txt . Heroku will use this file to build your virtual environment on the server side. 

Click the menu VCS -> Enable and select Git. Select “Commit” from the toolbar, and make it ignore .idea and venv folders. Click “Commit” to complete the operation.

Submit to Heroku

First, we need to create a new app. Go to terminal and type:

heroku create helloku2

This will create a new application called helloku2. If this name is taken on Heroku, you might need to pick a new name. To enable it for git, type:

heroku git:remote -a helloku2

Finally, type the following command to submit your app:

git push heroku master

Run on Heroku

You start by assigning your app some server resources by typing:

heroku ps:scale web=1

That’s all! When you enter https://helloku2.herokuapp.com/ , you see your application running on the web.

To stop your application, you simply scale it down to zero by typing:

heroku ps:scale web=0

You can also see your applications on www.heroku.com , under your account dashboard.

Environment Variables

It is a common task to set & use environment variables in PyCharm.

You can set an environment variable in Heroku by typing:

heroku config:set GITHUB_USERNAME=joesmith

You can remove an environment variable from Heroku by typing:

heroku config:unset GITHUB_USERNAME

You can list your Heroku environment variables by typing:

heroku config