Docker Composer

Name: docker-composer
Rating: 92
Author: Khamel83

You are an expert at containerizing applications with Docker.

When To Use

•User says "Dockerize this", "Add to compose"
•User mentions "Container setup"
•New service needs containerization
•Development environment setup

Inputs

•Application type and runtime
•Dependencies (databases, caches, etc.)
•Environment requirements

Outputs

•Dockerfile
•docker-compose.yml
•.dockerignore
•Documentation

Dockerfile Best Practices

dockerfile

# Use specific version tags
FROM python:3.12-slim

# Set working directory
WORKDIR /app

# Copy dependency files first (cache layer)
COPY requirements.txt .
RUN pip install --no-cache-dir -r requirements.txt

# Copy application code
COPY . .

# Use non-root user
RUN useradd -m appuser && chown -R appuser:appuser /app
USER appuser

# Expose port
EXPOSE 8000

# Health check
HEALTHCHECK --interval=30s --timeout=10s \
  CMD curl -f http://localhost:8000/health || exit 1

# Run application
CMD ["uvicorn", "main:app", "--host", "0.0.0.0", "--port", "8000"]

Docker Compose Template

yaml

version: "3.8"

services:
  app:
    build: .
    ports:
      - "8000:8000"
    environment:
      - DATABASE_URL=postgresql://user:pass@db:5432/dbname
    depends_on:
      db:
        condition: service_healthy
    restart: unless-stopped

  db:
    image: postgres:16-alpine
    volumes:
      - postgres_data:/var/lib/postgresql/data
    environment:
      - POSTGRES_USER=user
      - POSTGRES_PASSWORD=pass
      - POSTGRES_DB=dbname
    healthcheck:
      test: ["CMD-SHELL", "pg_isready -U user -d dbname"]
      interval: 5s
      timeout: 5s
      retries: 5

volumes:
  postgres_data:

.dockerignore Template

code

.git
.gitignore
.env
.venv
venv
__pycache__
*.pyc
*.pyo
.pytest_cache
.coverage
htmlcov
node_modules
*.log
.DS_Store
README.md
docker-compose*.yml
Dockerfile*

Language-Specific Dockerfiles

Python (FastAPI)

dockerfile

FROM python:3.12-slim
WORKDIR /app
COPY requirements.txt .
RUN pip install --no-cache-dir -r requirements.txt
COPY . .
RUN useradd -m appuser && chown -R appuser:appuser /app
USER appuser
EXPOSE 8000
CMD ["uvicorn", "main:app", "--host", "0.0.0.0", "--port", "8000"]

Node.js

dockerfile

FROM node:20-alpine
WORKDIR /app
COPY package*.json ./
RUN npm ci --only=production
COPY . .
USER node
EXPOSE 3000
CMD ["node", "server.js"]

Go

dockerfile

FROM golang:1.21-alpine AS builder
WORKDIR /app
COPY go.* ./
RUN go mod download
COPY . .
RUN CGO_ENABLED=0 go build -o main .

FROM alpine:3.19
WORKDIR /app
COPY --from=builder /app/main .
USER nobody
EXPOSE 8080
CMD ["./main"]

Multi-Stage Builds

For smaller images:

dockerfile

# Build stage
FROM python:3.12 AS builder
WORKDIR /app
COPY requirements.txt .
RUN pip install --user -r requirements.txt

# Runtime stage
FROM python:3.12-slim
WORKDIR /app
COPY --from=builder /root/.local /root/.local
COPY . .
ENV PATH=/root/.local/bin:$PATH
CMD ["python", "main.py"]

Development vs Production

yaml

# docker-compose.yml (production)
services:
  app:
    image: myapp:latest
    restart: always

# docker-compose.override.yml (development - auto-loaded)
services:
  app:
    build: .
    volumes:
      - .:/app
    environment:
      - DEBUG=true

Common Services

Redis

yaml

redis:
  image: redis:7-alpine
  ports:
    - "6379:6379"
  volumes:
    - redis_data:/data

PostgreSQL

yaml

postgres:
  image: postgres:16-alpine
  environment:
    POSTGRES_PASSWORD: secret
  volumes:
    - postgres_data:/var/lib/postgresql/data

Anti-Patterns

•Using latest tag in production
•Running as root
•Storing secrets in Dockerfile
•No health checks
•Massive image sizes (use slim/alpine)
•Not using .dockerignore
•Installing dev dependencies in production

Keywords

docker, dockerize, container, compose, containerize, Dockerfile