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Heroku: development and production settings

You have a project that you develop on your local machine and you deploy it on Heroku for instance. The two environments require different settings. For example, you test your app. with SQLite but in production you use PostgreSQL. How can the application configure itself to its environment?

I show you how to do it with Flask.

In your project folder:

$ heroku config:set HEROKU=1

It will create an environment variable at Heroku. These environment variables are persistent – they will remain in place across deploys and app restarts – so unless you need to change values, you only need to set them once.

Then create a config.py file in your project folder:

import os

class Config(object):
    DEBUG = False
    TESTING = False
    DATABASE_URI = 'sqlite://:memory:'

class ProductionConfig(Config):
    REDIS_URI = os.environ.get('REDISTOGO_URL')

class DevelopmentConfig(Config):
    DEBUG = True
    REDIS_URI = 'redis://localhost:6379'

class TestingConfig(Config):
    TESTING = True

Of course, you will have to customize it with your own settings.

Then, in your main file:

app = Flask(__name__)

if 'HEROKU' in os.environ:
    # production on Heroku
    # development on localhost

Now, if you want to access the configuration from different files of the project, use this:

from flask import current_app as app

Let’s see how to use Redis for instance. Apply the same idea with other databases too. Opening and closing can go in the before_request and teardown_request functions:

from flask import g
import redis

def before_request():
    g.redis = redis.from_url(app.config['REDIS_URI'])

def teardown_request(exception):
    pass    # g.redis doesn't need to be closed explicitly

If you need to access redis from other files, just import g and use g.redis .


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