How to depoy a Flask app to Heroku?

hello.py is a very simple Flask application. In this tutorial, we'll:

1. run it locally first, and then
2. depoly it to Heroku

Without further ado, let's get our hands dirty.

hello.py

import os
from flask import Flask

app = Flask(__name__)

@app.route('/')
def index():
    return '<h1>Hello World!</h1>'


if __name__ == '__main__':
#    app.run(debug=True)
    port = int(os.environ.get("PORT", 5000))
    app.run(host='0.0.0.0', port=port)

1. Run it locally

Please follow steps below:

mkdir hello-heroku
cd hello-heroku

# create and activate a virtual env
python3 -m venv venv
. venv/bin/activate
# the prompt will change here

# check the path of Python
which python

pip install flask
pip install gunicorn

gunicorn hello:app
# output on the terminal:
# * Running on http://0.0.0.0:5000/ (Press CTRL+C to quit)

Now, you can access above URL in the browser. "Hello Heroku!" will be displayed if everything goes all right.

2. Deploy it to Heroku from GitHub

1. Create a repo named "hello-heroku" on GitHub.
2. Create a Heroku account.
3. Install Heroku CLI.
4. Create an app on Heroku.

   heroku login
   heroku create hello-heroku-feici02
   

5. Configure the integratoin with GitHub on the "depoy" tab of this app.
6. Run the following commands to output a list of all the installed python packages

   pip freeze >! requirements.txt
   

7. Run the following command to create the "Procfile" which is required by Heroku to deploy the app.

   echo "web: gunicorn hello:app" > Procfile
   

8. Run the following command to push this app to GitHub.

   git init
   echo "venv\n*.pyc" > .gitignore
   git add -A
   git commit -m "initial commit"
   git remote add origin https://github.com/feici02/hello-heroku.git
   git push origin master
   

9. Check the logs to see if everything is OK.

   heroku logs --app hello-heroku-feici02
   

10. If there are no errors, you can access your app at: hello-heroku-feici02.herokuapp.com

3. Deploy it to Heroku directly

If you don't want to use GitHub, you can deploy the app created in Part 1 directly to Heroku. Here are the steps:

cd hello-heroku
git init
# steps to commit the files are omitted here
heroku apps:create hello-heroku-feici02-2
git remote -v
# a remote named heroku will be added to your repo automatically

git push heroku master
# Your app is up and running at: hello-heroku-feici02-2.herokuapp.com.

Reference

1. Getting Started on Heroku with Python
2. Starting a simple Flask app with Heroku