Docker + Django in 10 Days: From Zero to Production [Day: 05]

🎯 Goal of Day 5

By the end of today, you will:

• Understand why Docker Compose exists

• Run Django + PostgreSQL together

• Learn how services talk to each other

• Stop rebuilding containers on every code change

• Be very close to production-style setups

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❓ Why Docker Compose?

Yesterday’s problem:

• One container is fine

• Multiple containers = pain

Imagine running:

• Django

• PostgreSQL

• Redis

• Celery

Manually?

😵‍💫 No.

Docker Compose solves this:

One file → multiple services → one command

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📄 What Is Docker Compose?

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

You define everything in:

docker-compose.yml

Then run:

docker compose up

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🧠 Big Picture (Today)

Django Container  ↔  PostgreSQL Container

Important rule:

Containers talk using service names, not localhost.

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📁 Project Structure (Update)

Your project should now look like:

django-docker/
├── core/
├── manage.py
├── requirements.txt
├── Dockerfile
└── docker-compose.yml

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🐘 Step 1: Update requirements.txt

Django>=4.2,<5.0
psycopg2-binary>=2.9

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🐳 Step 2: Update Dockerfile (Small Change)

FROM python:3.12-slim

ENV PYTHONDONTWRITEBYTECODE=1
ENV PYTHONUNBUFFERED=1

WORKDIR /app

COPY requirements.txt .
RUN pip install --no-cache-dir -r requirements.txt

COPY . .

CMD ["python", "manage.py", "runserver", "0.0.0.0:8000"]

(No big change — good sign 👍)

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🧩 Step 3: Create docker-compose.yml

version: "3.9"

services:
  web:
    build: .
    container_name: django_app
    command: python manage.py runserver 0.0.0.0:8000
    volumes:
      - .:/app
    ports:
      - "8000:8000"
    depends_on:
      - db

  db:
    image: postgres:15
    container_name: postgres_db
    environment:
      POSTGRES_DB: django_db
      POSTGRES_USER: django_user
      POSTGRES_PASSWORD: django_pass
    volumes:
      - postgres_data:/var/lib/postgresql/data
    ports:
      - "5432:5432"

volumes:
  postgres_data:

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🧠 Very Important Concepts Here

🔹 services

Each service = one container.

🔹 build: .

Uses your Dockerfile.

🔹 volumes

.:/app

Means:

• Local code ↔ container code

• No rebuild needed on code change 🎉

🔹 depends_on

Starts DB before Django.

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🔌 Step 4: Update Django Database Settings

In settings.py:

DATABASES = {
    "default": {
        "ENGINE": "django.db.backends.postgresql",
        "NAME": "django_db",
        "USER": "django_user",
        "PASSWORD": "django_pass",
        "HOST": "db",   # service name, NOT localhost
        "PORT": "5432",
    }
}

⚠️ HOST = "db" is CRITICAL.

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▶️ Step 5: Run Everything

Stop previous containers:

docker compose down

Start new setup:

docker compose up --build

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🧪 Step 6: Run Migrations

Open a new terminal:

docker compose exec web python manage.py migrate

Create superuser:

docker compose exec web python manage.py createsuperuser

Visit:

http://127.0.0.1:8000/admin

🎉 Django + PostgreSQL is LIVE in Docker 🎉

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🧠 Networking Magic (Important)

Inside Docker:

• localhost → current container only

• db → PostgreSQL container

Docker Compose creates an internal network automatically.

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📚 Official Docs (Must Bookmark)

• Docker Compose overview
  https://docs.docker.com/compose/

• PostgreSQL image
  https://hub.docker.com/_/postgres

• Django PostgreSQL docs
  https://docs.djangoproject.com/en/stable/ref/databases/#postgresql-notes

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⚠️ Common Beginner Mistakes

• Using localhost for DB ❌

• Forgetting volumes → data loss

• Forgetting to run migrations

• Editing code but not using volumes

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📝 Homework (Very Important)

1. Start containers with docker compose up

2. Run migrations

3. Access admin panel

4. Stop containers

5. Restart and confirm data persists

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✅ End of Day 5 Summary

• You learned Docker Compose

• You ran multiple containers

• Django talks to PostgreSQL correctly

• You now have a real backend setup

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