1. Create a new directory with mkdir example;
2. Access such directory with cd example;
3. Create a virtual environment. I'm using venv (the command is python3 -m venv EXAMPLEENV) in this app, now access it with source example/bin/activate. To leave the virtual environment, just type deactivate EXAMPLEENV;
4. Install Django with pip install django and see which version it's installing. In my case, the version installed is Django 4.2.4. You'll need to know it to create a requirements.txt file for Docker;
5. Create a Django project with django-admin startproject exampleapp. Access the exampleapp folder with cd example app, perform a database migration django manage.py migrate and start the local server python manage.py runserver. You can now use your browser and go to http://localhost:8000 and should see something like Image 1. Warning: a different page may appear (they might change according to the installed Django version), but that doesn't mean something went wrong. Check the Django official documentation if something doesn't feel right.

Your project directory's tree should look like this:

example (this is the root folder of your project)
├── exampleapp
│   ├── exampleapp
│   │   ├── asgi.py
│   │   ├── __init__.py
│   │   ├── __pycache__
│   │   ├── settings.py
│   │   ├── urls.py
│   │   └── wsgi.py
│   ├── db.sqlite3
│   └── manage.py
└── EXAMPLEENV

1. Create the requirements.txt file in root/exampleapp/. There's more than one way to do it, but from the root folder of your project (example), you can enter cd exampleapp and then touch requirements.txt. In this file, we'll type the names and versions of the dependencies (packages your project can't work without, e.g. Django) so Docker will automatically download and add them to the project.

2. Add Django==VERSION to requirements.txt. VERSION should be the Django version intended to be used in this project. In my case, I'm adding Django==4.2.4.

3. Creating the first Dockerfile:

   1. In root/exampleapp, create a Dockerfile with touch Dockerfile.
   2. Add this to the newly created file:

   # using the official python image with Alpine Linux
   FROM python:3.10.12-alpine
   
   # to set the work directory
   WORKDIR /usr/src/app
   
   # python environment variables. Read more in https://docs.python.org/3/using/cmdline.html#envvar-PYTHONUNBUFFERED and https://docs.python.org/3/using/cmdline.html#envvar-PYTHONUNBUFFERED
   ENV PYTHONDONTWRITEBYTECODE 1
   ENV PYTHONUNBUFFERED 1
   
   # updating and system dependencies
   RUN apk update \
       && apk add postgresql-dev gcc python3-dev musl-dev
   
   # update pip, copy requirements.txt into the work directory, then install dependencies defined in requirements.txt
   RUN pip install --upgrade pip
   COPY ./requirements.txt .
   RUN pip install -r requirements.txt
   
   # copy everything inside this specific directory, and not all others, to the work directory. 
   COPY . .
   
   

4. Creating the Docker Compose file:

   1. Go to the root directory of your project (/example/), create a docker-compose.yml file with touch docker-compose.yml;
   2. Add this to the newly created file:

   services:
     web:
       build: ./exampleapp # this needs to be django's main folder
       command: python manage.py runserver 0.0.0.0:8000
       volumes:
         - ./exampleapp/:/usr/src/app # django's main folder:WORKDIR defined in /example/exampleapp/Dockerfile
       ports:
         - 8000:8000
       env_file:
         - ./.env.dev
   

5. Update Django settings:

   1. Open settings.py (located inside /example/exampleapp/exampleapp/settings.py);
   2. Add import os at the top of the file.
   3. Edit the following variables: DEBUG, ALLOWED_HOSTS, and SECRET_KEY. To simplify and make things more secure, we'll add variables that depend on .env files (defined on the example/docker-compose.yml). Edit each accordingly to my example:
      • DEBUG = os.getenv('DEBUG_STATUS', False) == 'True'
      • ALLOWED_HOSTS = os.getenv('ALLOWED_HOSTS', '127.0.0.1').split(',')
      • SECRET_KEY = os.getenv('SECRET_KEY') Docker will look for the value of each of the above inside .env files, according to the Compose configuration.

6. Create a .env.dev file in the project's root folder. I'm using touch .env.dev.

7. Add this to .env.dev (if you're in the right directory but can't see this file, check how to see hidden files in your Operating System):

SECRET_KEY=secret
DEBUG_STATUS=True
ALLOWED_HOSTS=localhost

8. You can now, in the project's root folder, type docker compose build to build the project's image (you might need to write sudo alongside with all the Docker related commands. In this case, it would be sudo docker compose build) and then docker compose up -d to run the container. After everything loaded, you can head to http://localhost:8000 to check if the container is working. If not, you may check for errors by typing docker compose logs -f. In order to stop the container(s), you can type docker compose down -v. The -v flag takes down any volumes that might be running (none so far, but we'll be adding some in the future).

If you've followed every step so far, your project directory should look like this:

example (project's root folder)
├── exampleapp
│   ├── exampleapp
│   ├── db.sqlite3
│   ├── Dockerfile
│   ├── manage.py
│   └── requirements.txt
├── docker-compose.yml
├── env
│   ├── bin
│   ├── include
│   ├── lib
│   ├── lib64 -> lib
│   └── pyvenv.cfg
├── LICENSE
└── README.md

1. We'll now a service for the database by editing example/docker-compose.yml. This is how the file should look like now:

services:
  web:
    build: ./exampleapp
    command: python manage.py runserver 0.0.0.0:8000
    volumes:
      - ./exampleapp/:/usr/src/app
    ports:
      - 8000:8000
    env_file:
      - ./.env.dev
    depends_on:
      - db
  db:
    image: postgres:15.4-alpine
    volumes:
      - postgres_data:/var/lib/postgresql/data/
    env_file:
      - ./.env.dev

volumes:
  postgres_data:

IMPORTANT: Note how the service web now depends on the new service db. Don't forget to add these lines. 2. Add new variables to the example/.env.dev file in order to configure the database. These will also be used by the settings.py file. Since this is only the development environment, you don't need focus on making the values extra safe. For the production environment, however, it's recommended you use secure values for your .env file. Since we're using Postgres, the value for the DB_ENGINE must not be changed (check Django's documentation on how to configure the database). These are the new lines:

POSTGRES_USER=user
POSTGRES_PASSWORD=pass
POSTGRES_DB=django_dev_db
DB_ENGINE=django.db.backends.postgresql
POSTGRES_HOST=db
POSTGRES_PORT=5432

3. On the root folder, enter the virtual environment (if you're not using it right now) and install the psycopg2-binary package by entering pip install psycopg2-binary. Pay attention to which version you installed (just like you did with Django) or type pip list to see the version installed.
4. Open your requirements.txt file (it's in the same folder as manage.py, and you can find it by typing, from the project's root folder, cd exampleapp/) and add the line psycopg2-binary==VERSION to it. This is how my file currently looks like:

Django==4.2.4
psycopg2-binary==2.9.7

5. Go to the settings.py file (example/exampleapp/exampleapp/settings.py) and change the DATABASES dictionary. Afterwards, it should look like this:

DATABASES = {
    'default': {
        'ENGINE': os.environ.get("DB_ENGINE"),
        'NAME': os.environ.get("POSTGRES_DB"),
        'USER': os.environ.get("POSTGRES_USER"),
        'PASSWORD': os.environ.get("POSTGRES_PASSWORD"),
        'HOST': os.environ.get("POSTGRES_HOST"),
        'PORT': os.environ.get("POSTGRES_PORT"),
    }
}

6. Testing:
   1. Bring down your containers and volume (if they're running) with docker compose down -v, build (again) the image and start the containers with docker compose up -d --build;
   2. Run the migrations with docker compose exec web python manage.py migrate --noinput. If you get the error django.db.utils.OperationalError: FATAL: database "django_dev_db" does not exist, bring down the containers and volume with docker compose down -v, and rebuild everything by typing docker compose up -d --build.
   3. Make sure the tables were created by typing sudo docker compose exec db psql --username=user --dbname=django_dev_db and then \l. Something like this should show up.

   django_dev_db=# \l
                                               List of databases
     Name      | Owner | Encoding |  Collate   |   Ctype    | ICU Locale | Locale Provider | Access privileges
---------------+-------+----------+------------+------------+------------+-----------------+-------------------
 django_dev_db | user  | UTF8     | en_US.utf8 | en_US.utf8 |            | libc            |
 postgres      | user  | UTF8     | en_US.utf8 | en_US.utf8 |            | libc            |
 template0     | user  | UTF8     | en_US.utf8 | en_US.utf8 |            | libc            | =c/user          +
               |       |          |            |            |            |                 | user=CTc/user
 template1     | user  | UTF8     | en_US.utf8 | en_US.utf8 |            | libc            | =c/user          +
               |       |          |            |            |            |                 | user=CTc/user
(4 rows)

4. Type \c to check with which user you're logged in. It should return something like:

django_dev_db=# \c
You are now connected to database "django_dev_db" as user "user".

5. To check the list of relations (or who owns what), type \dt. Result:

django_dev_db=# \dt
                  List of relations
 Schema |            Name            | Type  | Owner 
--------+----------------------------+-------+-------
 public | auth_group                 | table | user
 public | auth_group_permissions     | table | user
 public | auth_permission            | table | user
 public | auth_user                  | table | user
 public | auth_user_groups           | table | user
 public | auth_user_user_permissions | table | user
 public | django_admin_log           | table | user
 public | django_content_type        | table | user
 public | django_migrations          | table | user
 public | django_session             | table | user
(10 rows)

6. To quit the Postgres CLI, type \q.
7. Last but not least, type docker volume inspect example_postgres_data to make sure the Docker volume was created. My results:

[
    {
        "CreatedAt": "DATE",
        "Driver": "local",
        "Labels": {
            "com.docker.compose.project": "blog",
            "com.docker.compose.version": "2.17.3",
            "com.docker.compose.volume": "postgres_data"
        },
        "Mountpoint": "/var/lib/docker/volumes/blog_postgres_data/_data",
        "Name": "blog_postgres_data",
        "Options": null,
        "Scope": "local"
    }
]

The database is working, but that doesn't mean you'll be able to access http://localhost:8000 just yet. It was only after completing the following steps that it finally worked.

7. Setting up an entrypoint:
   1. Create a entrypoint.sh inside example/exampleapp/, the directory with manage.py. Add the following code inside it:

#!/bin/sh

if [  "DB_ENGINE" = "django.db.backends.postgresql" ]
then
    echo "Waiting for Postgres..."

    while ! nc -z $DB_HOST $DB_PORT; do
        sleep 0.1
    done

    echo "Postgres started!"
fi

python manage.py flush --no-input
python manage.py migrate

exec "$@"

Afterwards, make it an executable by typing chmod +x entrypoint.sh (you need to be in the same directory as the file). 2. Let's edit the Dockerfile (located in the same directory as entrypoint.sh and manage.py). We need to add lines so we can copy and work with entrypoint.sh, and then add one line to actually run the file. This is how the file will look like after the additions:

# using the official python image with Alpine Linux
FROM python:3.10.12-alpine

# to set the work directory
WORKDIR /usr/src/app

# python environment variables. Read more in https://docs.python.org/3/using/cmdline.html#envvar-PYTHONUNBUFFERED and https://docs.python.org/3/using/cmdline.html#envvar-PYTHONUNBUFFERED
ENV PYTHONDONTWRITEBYTECODE 1
ENV PYTHONUNBUFFERED 1

# updating and installing system dependencies
RUN apk update \
    && apk add postgresql-dev gcc python3-dev musl-dev

# update pip, copy requirements.txt into the work directory, then install dependencies defined in requirements.txt
RUN pip install --upgrade pip
COPY ./requirements.txt .
RUN pip install -r requirements.txt

# copy entrypoint.sh to the work directory, run a stream editor, then allow the file to be executed
COPY ./entrypoint.sh .
RUN sed -i 's/\r$//g' /usr/src/app/entrypoint.sh
RUN chmod +x /usr/src/app/entrypoint.sh

# copy everything inside this specific directory, and not all others, to the work directory.
COPY . .

# run as soon as the container is started
ENTRYPOINT ["/usr/src/app/entrypoint.sh"]

By the way, you'll need netcat to run entrypoint.sh. Alpine already comes with it so that's why I'm not downloading it, but make sure your container's OS has it as well.

8. Bring everything down with sudo docker compose down -v, and then rebuild and run the containers with sudo docker compose up -d --build.

I recommend everyone to only set up the production environment only after finishing the project.