Deploying Flask Apps to Heroku: 3 Examples

Deploying a Flask application to Heroku can seem daunting at first, but with the right steps, it can be a straightforward process. This guide will take you through three diverse examples of deploying a Flask application to Heroku, ensuring that you’ll feel confident in getting your app live and running. Let’s dive in!

Example 1: Basic Flask App Deployment

Context

This example focuses on a simple Flask application that displays a welcome message. It’s perfect for beginners who want to learn how to deploy a basic app.

To get started, ensure you have the following:

• A Heroku account
• The Heroku CLI installed on your machine
• A basic Flask app set up locally

## app.py
from flask import Flask

app = Flask(__name__)

@app.route('/')
def home():
    return 'Welcome to my Flask app!'

if __name__ == '__main__':
    app.run(debug=True)

To deploy this app to Heroku:

1. Create a requirements.txt file using pip freeze > requirements.txt.
2. Create a Procfile that tells Heroku how to run your app:

web: python app.py

3. Initialize a git repository (if not done yet):

   git init
   git add .
   git commit -m "Initial commit"
   

4. Log in to Heroku:

   heroku login
   

5. Create a new Heroku app:

   heroku create my-flask-app
   

6. Deploy the app:

   git push heroku master
   

7. Open your app in the browser:

   heroku open
   

Notes

• Make sure your app runs locally without errors before deploying.
• You can modify the Procfile if your app’s entry point is different.

Example 2: Flask App with Environment Variables

Context

In this example, we will deploy a Flask app that uses environment variables to store sensitive information such as API keys. This is great for real-world applications.

First, let’s create a Flask application that uses an environment variable:

## app.py
import os
from flask import Flask

app = Flask(__name__)

@app.route('/')
def home():
    api_key = os.getenv('API_KEY')
    return f'Your API Key is: {api_key}'

if __name__ == '__main__':
    app.run(debug=True)

To deploy this app:

1. Create a requirements.txt and Procfile as explained in the first example.
2. Log in to Heroku and create a new app:

heroku create my-flask-app-with-env

3. Set your environment variable on Heroku:

   heroku config:set API_KEY='your_api_key_here'
   

4. Deploy your app:

   git push heroku master
   

5. Open your app:

   heroku open
   

Notes

• Environment variables help keep sensitive data secure.
• To check your environment variables, use heroku config.

Example 3: Flask App with a Database

Context

This example illustrates deploying a Flask app that integrates with a database, specifically PostgreSQL. This setup is common for applications needing persistent data storage.

Let’s create a simple Flask application that connects to a PostgreSQL database:

## app.py
from flask import Flask, jsonify
from flask_sqlalchemy import SQLAlchemy

app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = os.getenv('DATABASE_URL')
app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = False

db = SQLAlchemy(app)

class User(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(80), nullable=False)

@app.route('/users')
def get_users():
    users = User.query.all()
    return jsonify([user.name for user in users])

if __name__ == '__main__':
    app.run(debug=True)

To deploy this app:

1. Create a requirements.txt and Procfile.
2. Log in to Heroku and create a new app:

heroku create my-flask-db-app

3. Add PostgreSQL to your app:

   heroku addons:create heroku-postgresql:hobby-dev
   

4. Set up your database:

   heroku run python -c 'from app import db; db.create_all()'
   

5. Deploy your app:

   git push heroku master
   

6. Open your app:

   heroku open
   

Notes

• Ensure you install Flask-SQLAlchemy and any other dependencies before deploying.
• The DATABASE_URL is automatically set by Heroku when you add the PostgreSQL addon.

These examples of deploying a Flask application to Heroku should give you a solid foundation to start from, whether you’re working on a simple app or one that requires more advanced features like environment variables and databases. Happy coding!