docker-helper

name	docker-helper
description	Docker and Docker Compose mastery for containers, images, networks, volumes, and debugging. Use when user asks to "build a container", "run docker", "debug container", "write dockerfile", "docker compose up", "check container logs", "optimize docker image", or any container operations.

Docker Helper

Essential Docker and Docker Compose commands and patterns.

Container Operations

# Run container
docker run -d --name myapp -p 8080:80 nginx
docker run -it --rm ubuntu bash  # Interactive, auto-remove

# With volume and env
docker run -d \
  -v $(pwd):/app \
  -e NODE_ENV=production \
  --name myapp \
  node:18 npm start

# List containers
docker ps          # Running
docker ps -a       # All

# Logs
docker logs myapp
docker logs -f myapp        # Follow
docker logs --tail 100 myapp

# Exec into container
docker exec -it myapp bash
docker exec -it myapp sh    # Alpine

# Stop/remove
docker stop myapp
docker rm myapp
docker rm -f myapp  # Force

Image Operations

# Build
docker build -t myapp:latest .
docker build -t myapp:v1.0 -f Dockerfile.prod .

# List/remove
docker images
docker rmi myapp:latest
docker image prune -a  # Remove unused

# Tag/push
docker tag myapp:latest registry.io/myapp:latest
docker push registry.io/myapp:latest

Docker Compose

# Start services
docker compose up -d
docker compose up -d --build  # Rebuild

# Stop
docker compose down
docker compose down -v  # Remove volumes

# Logs
docker compose logs -f
docker compose logs -f web

# Scale
docker compose up -d --scale web=3

# Exec
docker compose exec web bash

Compose File Pattern

# docker-compose.yml
services:
  web:
    build: .
    ports:
      - "3000:3000"
    volumes:
      - .:/app
      - /app/node_modules
    environment:
      - NODE_ENV=development
    depends_on:
      - db

  db:
    image: postgres:15
    volumes:
      - postgres_data:/var/lib/postgresql/data
    environment:
      POSTGRES_PASSWORD: secret

volumes:
  postgres_data:

Debugging

# Container inspection
docker inspect myapp
docker inspect --format '{{.NetworkSettings.IPAddress}}' myapp

# Resource usage
docker stats
docker stats myapp

# Processes in container
docker top myapp

# Filesystem changes
docker diff myapp

# Copy files
docker cp myapp:/app/file.txt ./
docker cp ./file.txt myapp:/app/

Cleanup

# Remove stopped containers
docker container prune

# Remove unused images
docker image prune -a

# Remove unused volumes
docker volume prune

# Remove everything unused
docker system prune -a --volumes

Dockerfile Best Practices

# Use specific tags
FROM node:18-alpine

# Set working directory
WORKDIR /app

# Copy package files first (layer caching)
COPY package*.json ./
RUN npm ci --only=production

# Copy source
COPY . .

# Non-root user
RUN addgroup -g 1001 appgroup && \
    adduser -S -u 1001 -G appgroup appuser
USER appuser

# Expose port
EXPOSE 3000

# Health check
HEALTHCHECK --interval=30s --timeout=3s \
  CMD wget -q --spider http://localhost:3000/health || exit 1

CMD ["node", "server.js"]

Reference

For multi-stage builds, networking, and optimization: references/advanced.md