Heroku Postgres - How come my production database is working, even though not listed in settings.py - Django?

Question

I configured my database in Heroku several months ago so don't remember exact steps I took. I'm using the Heroku-Postgres add-on: https://devcenter.heroku.com/articles/heroku-postgresql

I have a DATABASE_PASS listed as a config var in Heroku. And I have a config var for DATABASE_URL

In my settings.py file I only have the following as it relates to my database. Why is my app still working in production on Heroku if DATABASES variable is referring to localhost only?

DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.postgresql',
        'NAME': 'my_dev',
        'USER': 'postgres',
        'PASSWORD': os.environ.get('DATABASE_PASS'),
        'HOST': 'localhost',
        'PORT': '5410',
    }
}

The Heroku-Postgres documentation states the following:

The value of your app’s DATABASE_URL config var might change at any time. You should not rely on this value either inside or outside your Heroku app.

Am I doing something wrong? Should I not rely on DATABASE_URL as a config var?

Additional Detail - I am using the django-heroku pip package.

Answer 1

Why is my app still working in production on Heroku if DATABASES variable is referring to localhost only?

Additional Detail - I am using the django-heroku pip package.

django-heroku does quite a lot, including setting up your database from the DATABASE_URL environment variable automatically:

This will automatically configure DATABASE_URL, ALLOWED_HOSTS, WhiteNoise (for static assets), Logging, and Heroku CI for your application.