Deploy an application on Heroku

What is Heroku?

Heroku is a cloud platforme to host applications, databases and other services in several languages. It is easy and flexible to use. It is free, with paid specialized memberships.

Getting Started on Heroku

Create an account with Heroku. We need also to install Heroku CLI(Command Line Interface) to run commands from the terminal to create a Heroku app.

Install Heroku with Homebrew

brew tap heroku/brew && brew install heroku

After installing heroku you can run it using hroku login and provide auth info. After that you can run commands to create your heroku app.

Heroku Deployment

To configure your app such that it runs properly on Heroku, you should follow those steps:

Creating and updating requirements.txt file to install depndecies using this command every time you add new dpendency
```
pip freeze > requirements.txt
```
Setting up your environement varibales.
Using a Procfile, using gunicorn to run the application

Deplyment Configuration

Environment Configuration

Set up the envirement variables on setup.sh. We can also setup them using the web interface by going to settings then Reveal Config Vars you can define here a varibales in the table that appear just like you did in setup.sh.

Gunicorn

Gunicorn is a pure-Python HTTP server for WSGI applications. We will use it to deploy our application.

Install by:
```
pip install gunicorn
```
Create Procfile. include one line to instruct Heroku correctly for us: web: gunicorn app:app. app is the name of your app or whatever is your application name and make sure your app is housed in that app.py or whatever you name your app file.

Note: the app name should be the name that we find int he main others ways you will get an error => you're telling gunicorn that your application's entry point is the app variable in th main module, if you use another name in the main it will not work :p. So be careful. Read this question=>Failed to find application object 'app' in 'main' - Heroku CLI for more details

Databse Migration

To allow heroku run all your migrations to the database you have hosted on the platforme, your application need to include manage.py file.

First istall those package:

pip install flask_script
pip install flask_migrate
pip install psycopg2-binary

mange.py should contain the following code

from flask_script import Manager
from flask_migrate import Migrate, MigrateCommand

from app import app
from models import db

migrate = Migrate(app, db)
manager = Manager(app)

manager.add_command('db', MigrateCommand)


if __name__ == '__main__':
    manager.run()

We can run our local migrations using our manage.py file, to mirror how Heroku will run behind the scenes for us when we deploy our app:
```
python manage.py db init
python manage.py db migrate
python manage.py db upgrade
```
Those last commands are the essential process that Heroku will run to ensure your database is architected properly. We, however, won't need to run them again unless we're testing the app locally.

Ps: Wenever you install new package remeber to freeze your requirements.txt

Your file structure should be like this

> __pycache__
> migrations
.gitignore
app.py
manage.py 
models.py 
Procfile
requirements.text
Setup.sh

Deploy and Test

After you congigure you need to add deploy it.

Create Heroku app:

run this command to create hroku app. The output will include git url for your Heroku app. Copy it to use it later.
```
heroku create name_of_your_app
```

Add git remote for heroku to local repo

Using the git url obtained from the last step, in terminal run
```
git remote add heroku heroku_git_url
```

Add postgresql add on for your database

Heroky has an addon for apps for a prostgresql databse instance: run this command to create your db and connect it to your app
```
heroku addons:create heroku-postgresql:hobby-dev --app name_of_your_application
```

heroku-postgresql is the name of the addon hobby-dev specifies the tier of the addon, in this case free version which has limit on amount of data that will store.

Run the under command to check your config vars in heroku
```
heroku config --app name_of_your_application
```

Fix config in Heroku

Go setting. Reval your config var and start add all the required env vars for your app. For the pupose of this app add additional one - ‘EXCITED’ and set it to true or false in all lowercase.

Push it!

```
git push heroku master
```

Run migrations

Once your app is deployed, run migrations by running: heroku run python manage.py db upgrade --app name_of_your_application

That's it!

Now we have a live app :D. Open it from the heroku dashboard and see it live :D. Make additional requests using curl or Postman as you build your application and make more complex endpoints :).

Credit

All credits go for udacity full stack amazing nanodegree and it section Introduction to Heroku :D.

DinaTaklit / HerokuSample