Docker Compose – Multi Container Applications

Docker Compose – Multi Container Applications

When building real applications, you need:

  • Django

  • PostgreSQL

  • Redis

  • Celery

Managing multiple containers manually is hard.

Enter Docker Compose

Docker Compose allows defining multi-container applications using YAML.

Example docker-compose.yml

version: "3.9"

services:
  web:
    build: .
    command: gunicorn project.wsgi:application --bind 0.0.0.0:8000
    volumes:
      - .:/code
    ports:
      - "8000:8000"
    depends_on:
      - db

  db:
    image: postgres:15
    environment:
      POSTGRES_DB: mydb
      POSTGRES_USER: myuser
      POSTGRES_PASSWORD: mypassword

Run Compose

docker-compose up --build

Docker Volumes & Networks
Volumes
Used for:
  • Persisting database data
  • Sharing files
docker volume create myvolume
Networks
Docker automatically creates bridge networks, but you can create custom ones:
docker network create mynetwork

Docker for Production (Best Practices)
Security Best Practices
  • Use official base images
  • Use specific version tags
  • Avoid running as root
  • Use .dockerignore
  • Keep images small
Multi-Stage Builds
FROM python:3.12 as builder

WORKDIR /app
COPY requirements.txt .
RUN pip install --user -r requirements.txt

FROM python:3.12-slim
WORKDIR /app
COPY --from=builder /root/.local /root/.local
COPY . .

CMD ["python", "app.py"]
Docker + CI/CD
Docker works perfectly with:
  • GitHub Actions
  • GitLab CI/CD
  • Jenkins
Example flow:
  1. Push code
  2. Build Docker image
  3. Push to Docker Hub
  4. Deploy to server
Docker in Cloud Deployment
Docker can be deployed to:
  • Amazon ECS
  • Kubernetes
  • Google Kubernetes Engine
  • Azure Kubernetes Service


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