Deploy Flask app to Heroku

Flask is a customized-free framework.
I have the Flask application deployed to Heroku.

Development

• Python 3.7.5
• Flask 1.1.1
• SQL Alchemy
• Flask Migrate

When it comes to something tutorials, db.create_all() is useful. But this is not available to record when db migrated. So, you should use Flask Migrate if you run the application on production.

Initial commit

Set up requires folders/files. You may see a lot of patterns for Flask application on references.

app/
├── manage.py
├── main
│   ├── __init__.py
│   ├── views.py
│   ├── config.py
│   ├── models.py
│   ├── app.db
│   ├── static/
│   ├── templates/
│   └── instance
│       └──application.cfg
├── Procfile
├── requirements.txt
├── migrations/
└── venv/

Create a project

$ cd APP
$ mkdir -p main/{static,templates,instance}
$ cd main
$ touch manage.py requirements.txt Procfile
$ touch main/{__init__,views,models,config}.py

Add stylesheet or HTML if you wanted. This time, I want to focus on waking through it by focusing on backend stuff.

manage.py

from main import app
app.run()

main/init.py

from flask import Flask

app = Flask(__name__)

import main.views

main/views.py

from flask import render_template
from main import app, db

@app.route('/')
def home():
    return render_template('home/index.html')

Set up configuration

main/config.py

import os

class BaseConfig(object):
    SQLALCHEMY_TRACK_MODIFICATIONS = False  

class DevelopmentConfig(BaseConfig):
    DEBUG = True
    TESTING = True
    SQLALCHEMY_DATABASE_URI = 'sqlite:///app.db'

class ProductionConfig(BaseConfig):
    DEBUG = True
    TESTING = True
    SQLALCHEMY_DATABASE_URI=os.environ.get('DATABASE_URL')

config = {
    "default": "main.config.BaseConfig",
    "development": "main.config.DevelopmentConfig",
    "production": "main.config.ProductionConfig",
}

def configure_app(app):
    config_name= os.getenv('FLASK_ENV')
    app.config.from_object(config[config_name])
    app.config.from_pyfile('application.cfg', silent=True)

You can set up FLASK_ENV like export FLASK_ENV=development. I have just divided development and production. on.environ.get('DATABASE_URL') is just for connecting with a database in Heroku.

instance/application.cfg

SECRET_KEY='XXXXXXXXXXXXXXXXXXX'

Caution: instances folders should be added on .gitignore.

Initialized configuration

Add to __init__.py.

from main.config import configure_app

app = Flask(__name__, instance_relative_config=True)
configure_app(app)

Deploy to Heroku

Install gunicorn and psycpg2

$ pip install gunicorm
$ pip install psycopg2

Add Procfile

web: gunicorn main:app --log-file -

Add libraries info to requirements

$ pip freeze > requirements.txt

Deploy!

$ heroku create flask-app
$ git push heroku master
$ heroku config:set FLASK_APP=main
$ heroku config:set FLASK_ENV=production

Set up Database

Create User model

from main import db

class User(db.Model):
    __tablename__ = 'users'
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String)
    email = db.Column(db.String, unique=True)

    def __repr__(self):
        return '<User %r>' % self.name

Install flask_migrate and SQL Alchemy

$ pip install flask_migrate
$ pip install flask_sqlalchemy

Initialize model

Add to __init__.py.

from flask_sqlalchemy import SQLAlchemy
from flask_migrate import Migrate

db = SQLAlchemy(app)
migrate = Migrate(app, db)
db.init_app(app)

import main.models

Migrate

$ flask db init
$ flask db migrate
$ flask db upgrade

Migrate in Heroku

Add libraries to requirements

$ pip freeze > requirements.txt

Migration!

$ heroku run flask db upgrade

You don't need to db init or db migrate. But you have to deploy files including migrations.