Environment
settings with Django

Florian Demmer

django-environ

Django Meetup, 2017-11-07

The Twelve-Factor App

III. Config

Store config in the environment

https://12factor.net/config

A little history

• django-admin startproject myproject

• myproject/settings.py

• from django.conf import settings

• settings are at "myproject.settings"
   
• create myproject/local_settings.py
• import at end of myproject/settings.py
  → .gitignore!
  → multiple "locals" ... environments, stages?

Config per stage

• make settings a package, add "stages":
  • myproject/settings/__init__.py
    from . base import *
  • myproject/settings/base.py
    → previously settings.py
  • myproject/settings/dev.py
    from . base import *
    → plus "local" settings
     
• settings are at "myproject.settings"
• settings are at "myproject.settings.dev"

Tell Django about stages

• "myproject.settings" and "myproject.settings.dev"
• using the environment!
   

• in manage.py and wsgi.py:

  os.environ.setdefault(
    'DJANGO_SETTINGS_MODULE', 
    'myproject.settings'
  )

• run:
  DJANGO_SETTINGS_MODULE=myproject.settings.dev ./manage.py runserver

More fine grained settings

• eg. SECRET_KEY or passwords
   

• export SECRET_KEY=foobar
  
  $ python3 -c "import os; print(os.environ['SECRET_KEY'])"
  
  foobar
  
  

• works well with just strings

Introducing django-environ

• $ export CACHE_URL=redis://localhost:6379/0
  
  $ python -c "
  import environ; 
  env=environ.Env(); 
  print(env.cache())
  "
  
  {
    'LOCATION': 'redis://localhost:6379/0', 
    'BACKEND': 'django_redis.cache.RedisCache'
  }
  

Custom env var and defaults

• $ python -c "
  import environ; 
  env=environ.Env(); 
  print(
    env.cache(
      'MEMCACHED_URL',
      default='locmemcache://unique-snowflake')
  )"
  
  {
    'LOCATION': 'unique-snowflake', 
    'BACKEND': 'django...locmem.LocMemCache'
  }
  

More parameters

• $ export DATABASE_URL=postgresql://app:password@localhost:5432/app?ATOMIC_REQUESTS=1 
  
  $ python -c "import environ; env=environ.Env(); print(env.db())"
  
  {'ENGINE': 'django...postgresql_psycopg2', 
  'HOST': 'localhost', 'ATOMIC_REQUESTS': True, 'USER': 'app', 'OPTIONS': {}, 'PASSWORD': 'password', 'PORT': 5432, 'NAME': 'app'}
  
  

Required settings

• $ python -c "import environ; env=environ.Env(); print(env.db(NO_DATABASE_URL))"
  
  Traceback (most recent call last):
   File "<string>", line 1, in <module>
   File ".../django-environ/environ/environ.py", line 207, in db_url
      return self.db_url_config(self.get_value(var, default=default), engine=engine)
   File ".../django-environ/environ/environ.py", line 280, in get_value
      raise ImproperlyConfigured(error_msg)
  django.core.exceptions.ImproperlyConfigured: Set the DATABASE_URL environment variable

Datatypes

• $ export BOOL_=1
  
  $ python -c "import environ; env=environ.Env(); print(env.bool('BOOL_'))"
  
  True

• $ export FLOAT_=3,14
  
  $ python -c "import environ; env=environ.Env(); print(env.float('FLOAT_'))"
  
  3.14

Datatypes

• $ export LIST_=a,b,c,d,1,2,3
  
  $ python -c "import environ; env=environ.Env(); print(env.list('LIST_'))"
  
  ['a', 'b', 'c', 'd', '1', '2', '3']
  
  

• $ export DICT_=foo=bar,spam=42,ham=3.14
  
  $ python -c "import environ; env=environ.Env(); print(env.dict('DICT_'))"
  
  {'foo': 'bar', 'ham': '3.14', 'spam': '42'}

Managing environments

• .bashrc or .profile
• direnv (https://direnv.net)
   
• let django-environ read a file

  • $ python -c "
    import environ; 
    env=environ.Env(); 
    environ.Env.read_env('.env')
    "

• with docker-compose
  • ...

All the things

• https://12factor.net/config

• https://django-environ.readthedocs.io/en/latest/

• https://github.com/fdemmer/django-environ

• my twitter: @fdemmer

• slides: https://slides.com/fdemmer