Docker Patterns Skill

Patterns for building and running Docker containers.

Multi-Stage Builds

Node.js Application

dockerfile

# Stage 1: Dependencies
FROM node:20-alpine AS deps
WORKDIR /app
COPY package*.json ./
RUN npm ci

# Stage 2: Builder
FROM node:20-alpine AS builder
WORKDIR /app
COPY --from=deps /app/node_modules ./node_modules
COPY . .
RUN npm run build

# Stage 3: Production
FROM node:20-alpine AS production
WORKDIR /app

ENV NODE_ENV=production

# Create non-root user
RUN addgroup -g 1001 -S appgroup && \
    adduser -S appuser -u 1001

# Copy only production dependencies
COPY package*.json ./
RUN npm ci --only=production && \
    npm cache clean --force

# Copy built application
COPY --from=builder /app/dist ./dist

USER appuser

EXPOSE 3000
CMD ["node", "dist/index.js"]

Next.js Application

dockerfile

FROM node:20-alpine AS base

# Dependencies
FROM base AS deps
WORKDIR /app
COPY package*.json ./
RUN npm ci

# Builder
FROM base AS builder
WORKDIR /app
COPY --from=deps /app/node_modules ./node_modules
COPY . .
RUN npm run build

# Production
FROM base AS runner
WORKDIR /app

ENV NODE_ENV=production
ENV NEXT_TELEMETRY_DISABLED=1

RUN addgroup -g 1001 -S nodejs && \
    adduser -S nextjs -u 1001

COPY --from=builder /app/public ./public
COPY --from=builder --chown=nextjs:nodejs /app/.next/standalone ./
COPY --from=builder --chown=nextjs:nodejs /app/.next/static ./.next/static

USER nextjs

EXPOSE 3000
ENV PORT=3000

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

Optimization Patterns

Layer Caching

dockerfile

# Bad: Copies everything, invalidates cache on any change
COPY . .
RUN npm install && npm run build

# Good: Separate dependency and code layers
COPY package*.json ./
RUN npm ci
COPY . .
RUN npm run build

Reduce Image Size

dockerfile

# Use Alpine base images
FROM node:20-alpine

# Clean up in same layer
RUN apk add --no-cache \
      git \
      curl \
    && npm install -g pnpm \
    && rm -rf /var/cache/apk/*

# Use multi-stage to exclude build tools
FROM node:20-alpine AS builder
RUN npm install -g typescript
COPY . .
RUN tsc

FROM node:20-alpine
COPY --from=builder /app/dist ./dist

.dockerignore

code

# .dockerignore
node_modules
.git
.gitignore
*.md
.env*
.vscode
coverage
.nyc_output
dist
.next
Dockerfile*
docker-compose*

Security Patterns

Non-Root User

dockerfile

# Create user in base image
RUN addgroup -g 1001 -S app && \
    adduser -S -u 1001 -G app app

# Set ownership
COPY --chown=app:app . .

# Switch to non-root
USER app

Read-Only Filesystem

dockerfile

# In Dockerfile
USER app

# In docker-compose.yml
services:
  app:
    read_only: true
    tmpfs:
      - /tmp
      - /var/run

Scan for Vulnerabilities

yaml

# GitHub Actions
- name: Scan image
  uses: aquasecurity/trivy-action@master
  with:
    image-ref: myapp:latest
    format: 'table'
    exit-code: '1'
    severity: 'CRITICAL,HIGH'

Health Checks

dockerfile

HEALTHCHECK --interval=30s --timeout=3s --start-period=5s --retries=3 \
  CMD wget --no-verbose --tries=1 --spider http://localhost:3000/health || exit 1

# Alternative with curl
HEALTHCHECK --interval=30s --timeout=3s \
  CMD curl -f http://localhost:3000/health || exit 1

Environment Configuration

Build Arguments

dockerfile

ARG NODE_ENV=production
ARG BUILD_DATE
ARG VERSION

ENV NODE_ENV=${NODE_ENV}

LABEL org.opencontainers.image.created=${BUILD_DATE}
LABEL org.opencontainers.image.version=${VERSION}

Runtime Environment

dockerfile

# Default values
ENV NODE_ENV=production \
    PORT=3000 \
    LOG_LEVEL=info

# Values from docker run -e
# docker run -e DATABASE_URL=postgres://...

Docker Compose Patterns

Development

yaml

version: '3.8'

services:
  app:
    build:
      context: .
      target: deps
    volumes:
      - .:/app
      - /app/node_modules
    ports:
      - "3000:3000"
    environment:
      - NODE_ENV=development
    command: npm run dev

Production

yaml

version: '3.8'

services:
  app:
    image: myapp:${VERSION:-latest}
    restart: unless-stopped
    ports:
      - "3000:3000"
    environment:
      - NODE_ENV=production
    deploy:
      replicas: 3
      resources:
        limits:
          cpus: '0.5'
          memory: 512M
    healthcheck:
      test: ["CMD", "curl", "-f", "http://localhost:3000/health"]
      interval: 30s
      timeout: 10s
      retries: 3

Service Dependencies

yaml

services:
  app:
    depends_on:
      db:
        condition: service_healthy
      redis:
        condition: service_started

  db:
    image: postgres:15
    healthcheck:
      test: ["CMD-SHELL", "pg_isready -U postgres"]
      interval: 5s
      timeout: 5s
      retries: 5

  redis:
    image: redis:7-alpine

Networking

yaml

services:
  frontend:
    networks:
      - frontend

  backend:
    networks:
      - frontend
      - backend

  database:
    networks:
      - backend

networks:
  frontend:
  backend:
    internal: true  # No external access

Integration

Used by:

•infrastructure-engineer agent
•cicd-engineer agent