Python Flask Heroku Demo

Demonstration of Python with Flask (REST API) and a deployment to Heroku

Goals:

Create a simple REST application
On the local machine we want that the API /greeting returns “Hello World from localhost”
Deployment to Heroku
On the Heroku deployment we want that the API /greeting returns “Hello World from Heroku”

Dependencies

pip  install flask
pip install python-dotenv

# For Heroku
pip install gunicorn

# Save dependencies to requirements.txt
python3 -m pip freeze > requirements.txt

Python Flask project

File: app.py

from flask import Flask
import os

app = Flask(__name__)


@app.route("/greeting")
def greeting():
    return os.environ["MESSAGE"]


if __name__ == '__main__':
    app.run(host='0.0.0.0', port=8080)

File: .env

MESSAGE=Hello World from localhost

Run the application

python3 app.py

Validate the response

curl http://127.0.0.1:8080/greeting

# Should print: Message: Hello World from localhost

Git

git init

File .gitignore

venv
.git
__pycache__
.idea

Commit the files to git. And after checkout to the master branch.

git checkout -b master

Heroku Deployment

Create a Heroku account
Install Heroku CLI

File: Procfile

web: gunicorn app:app

Create the Heroku application

heroku create

# Returns
# > Creating app... done, ⬢ murmuring-plains-11587
# > https://murmuring-plains-11587.herokuapp.com/ | https://git.heroku.com/murmuring-plains-11587.git

git push heroku master

# After the git push Heroku should build and start the application
# Show the logs
heroku logs --tail

Set the environment variable

heroku config:set MESSAGE="Hello World from Heroku" -a murmuring-plains-11587

Validate the deployment

Validate the response

curl https://murmuring-plains-11587.herokuapp.com/greeting

# Should print: Message: Hello World from Heroku