In the last post I covered starting a new Django project with Docker, and how to build a custom container image for my project, but what I haven’t covered is how to use a Database and how persist your data since all data stored in the container ephemeral and would only exist during the life span of the container.

Instead of managing the Database inside my container we will use a ready made container, in my case I am going to use Postgres, and to solve data persistence issue we are going to mount Postgres data directory into a named volume.

But what about telling my Django app where to find the Postgres instance! Luckily this part is easily solved with the use of Docker Compose

Compose is a tool for defining and running multi-container Docker applications

We start with creating a new docker-compose.yml file describing what services our application consist of:

version: "3"
services:

  db:
    image: postgres
    restart: always
    environment:
      POSTGRES_DB: dj
      POSTGRES_USER: dj
      POSTGRES_PASSWORD: should_use_env
    volumes:
      - db-data:/var/lib/postgresql/data
    networks:
      - backend

  web:
    build: .
    restart: always
    depends_on:
      - db
    ports:
      - 8000:8000
    environment:
      POSTGRES_DB: dj
      POSTGRES_USER: dj
      POSTGRES_PASSWORD: should_use_env
      POSTGRES_HOST: db
    volumes:
      - .:/app
    networks:
      - backend

networks:
  backend:

volumes:
  db-data:

We need to change some settings in our Django app to add Postgres support, by adding the following line to requirements.txt:

psycopg2==2.7.3.2

and change our database settings by changing the DATABASE section in apps/apps/settings.py:

DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.postgresql_psycopg2',
        'NAME': os.environ.get('POSTGRES_DB', ''),
        'USER': os.environ.get('POSTGRES_USER', ''),
        'PASSWORD': os.environ.get('POSTGRES_PASSWORD', ''),
        'HOST': os.environ.get('POSTGRES_HOST', ''),
    }   
}

That’s all we need to change, we can now start our Docker compose application using the following command:

docker-compose up -d

and to execute more commands (e.g. DB migrations) on the running instance:

docker-compose exec web ./apps/manage.py migrate 
docker-compose exec web ./apps/manage.py createsuperuser

Note: dockerdjango is the name of the directory we are running the command from, you can use docker ps to find out your instances name too.

• django
• docker
• linux
• python