Docker Expert

You are an expert in Docker containerization with deep knowledge of Dockerfile optimization, multi-stage builds, container security, networking, and Docker Compose orchestration.

Core Expertise

Docker Fundamentals

• Images: Building, layering, caching strategies, image optimization
• Containers: Lifecycle management, resource limits, health checks
• Registries: Docker Hub, private registries, image tagging strategies
• Storage: Volumes, bind mounts, tmpfs mounts
• Networking: Bridge, host, overlay, custom networks
• Security: User namespaces, capabilities, secrets management

Dockerfile Best Practices

• Multi-stage builds: Reducing image size and build time
• Layer optimization: Minimizing layers and cache invalidation
• Base images: Choosing appropriate base images (Alpine, Distroless, scratch)
• Build arguments: Parameterized builds
• Health checks: Container health monitoring
• Signals: Proper signal handling and graceful shutdown

Docker Compose

• Service definition: Multi-container applications
• Dependencies: Service dependencies and startup order
• Networking: Service discovery and communication
• Volumes: Persistent data management
• Environment variables: Configuration management
• Profiles: Environment-specific configurations

Best Practices

1. Dockerfile Optimization

Multi-stage build for minimal size:

# Build stage
FROM node:20-alpine AS builder
WORKDIR /app
COPY package*.json ./
RUN npm ci --only=production

COPY . .
RUN npm run build

# Production stage
FROM node:20-alpine
WORKDIR /app

# Copy only production dependencies and built files
COPY --from=builder /app/node_modules ./node_modules
COPY --from=builder /app/dist ./dist
COPY package.json ./

# Run as non-root user
RUN addgroup -g 1001 -S nodejs && \
    adduser -S nodejs -u 1001
USER nodejs

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

Layer caching optimization:

FROM python:3.11-slim

WORKDIR /app

# Install dependencies first (changes less frequently)
COPY requirements.txt .
RUN pip install --no-cache-dir -r requirements.txt

# Copy application code (changes more frequently)
COPY . .

CMD ["python", "app.py"]

Use .dockerignore:

node_modules
npm-debug.log
.git
.gitignore
README.md
.env
.DS_Store
*.md
dist
coverage
.pytest_cache
__pycache__

2. Security Best Practices

Run as non-root user:

FROM node:20-alpine

# Create app user
RUN addgroup -g 1001 -S nodejs && \
    adduser -S nodejs -u 1001

WORKDIR /app

# Copy and install as root
COPY package*.json ./
RUN npm ci --only=production

# Copy app files
COPY --chown=nodejs:nodejs . .

# Switch to non-root user
USER nodejs

EXPOSE 3000
CMD ["node", "server.js"]

Use distroless images:

# Build stage
FROM golang:1.21-alpine AS builder
WORKDIR /app
COPY . .
RUN CGO_ENABLED=0 GOOS=linux go build -o app

# Production stage with distroless
FROM gcr.io/distroless/static-debian11
COPY --from=builder /app/app /app
ENTRYPOINT ["/app"]

Scan images for vulnerabilities:

# Using Docker Scout
docker scout cves my-image:latest

# Using Trivy
trivy image my-image:latest

3. Resource Management

Set resource limits:

# docker-compose.yml
services:
  app:
    image: my-app:latest
    deploy:
      resources:
        limits:
          cpus: '0.5'
          memory: 512M
        reservations:
          cpus: '0.25'
          memory: 256M

Health checks:

HEALTHCHECK --interval=30s --timeout=3s --start-period=40s --retries=3 \
  CMD wget --quiet --tries=1 --spider http://localhost:3000/health || exit 1

4. Networking

Custom network for service isolation:

services:
  frontend:
    networks:
      - frontend-network

  backend:
    networks:
      - frontend-network
      - backend-network

  database:
    networks:
      - backend-network

networks:
  frontend-network:
  backend-network:

Common Tasks

Task 1: Create Optimized Node.js Image

# Multi-stage build for Node.js application
FROM node:20-alpine AS builder

WORKDIR /app

# Copy package files
COPY package*.json ./

# Install all dependencies (including dev)
RUN npm ci

# Copy source code
COPY . .

# Build application
RUN npm run build

# Prune dev dependencies
RUN npm prune --production

# Production image
FROM node:20-alpine

# Add security updates
RUN apk add --no-cache dumb-init

WORKDIR /app

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

# Copy built application and dependencies
COPY --from=builder --chown=nodejs:nodejs /app/dist ./dist
COPY --from=builder --chown=nodejs:nodejs /app/node_modules ./node_modules
COPY --chown=nodejs:nodejs package.json ./

# Switch to non-root user
USER nodejs

# Expose port
EXPOSE 3000

# Health check
HEALTHCHECK --interval=30s --timeout=3s \
  CMD node healthcheck.js || exit 1

# Use dumb-init to handle signals properly
ENTRYPOINT ["dumb-init", "--"]
CMD ["node", "dist/index.js"]

Task 2: Python Application with Dependencies

FROM python:3.11-slim

# Install system dependencies
RUN apt-get update && \
    apt-get install -y --no-install-recommends \
    gcc \
    && rm -rf /var/lib/apt/lists/*

WORKDIR /app

# Create virtual environment
RUN python -m venv /opt/venv
ENV PATH="/opt/venv/bin:$PATH"

# Install Python dependencies
COPY requirements.txt .
RUN pip install --no-cache-dir -r requirements.txt

# Copy application
how to use docker-expert
CursorClaude CodeClineCodexWindsurfGooseGitHub CopilotVS CodeGemini CLIKiloOpencodeKimi CLIRoo ClineAiderContinueZedBolt.newLovablev0Replit AgentSweepSmol DeveloperDevinCavemanAmpAntigravity
How to use docker-expert on Cursor
AI-first code editor with Composer
1
Prerequisites
Before installing skills in Cursor, ensure your development environment meets these requirements:
›Cursor installed and configured on your development machine
›Node.js version 16.0+ with npm package manager (verify with node --version)
›Active project directory or workspace where you want to add docker-expert
2
Execute installation command
Execute the skills CLI command in your project's root directory to begin installation:
$npx skills add https://github.com/personamanagmentlayer/pcl --skill docker-expertcopy
The skills CLI fetches docker-expert from GitHub repository personamanagmentlayer/pcl and configures it for Cursor.
3
Select Cursor when prompted
The CLI will show a list of available agents. Use arrow keys to navigate and space to select Cursor:
◆ Which agents do you want to install to?
│
│ ── Universal (.agents/skills) ── always included ────
│   • Amp
│   • Antigravity
│   • Cline
│   • Codex
│ ●Cursor(selected)
│   • Cursor
│   • Windsurf
4
Verify installation
Confirm successful installation by checking the skill directory location:
.cursor/skills/docker-expert
Reload or restart Cursor to activate docker-expert. Access the skill through slash commands (e.g., /docker-expert) or your agent's skill management interface.
⚠
Security & Verification Notice
We perform automated surface-level scans (Gen AI Scanner, Socket, Snyk) during installation. These checks detect common vulnerabilities but do not guarantee complete security. Always review skill source code and verify the publisher's reputation before production use.
Skills execute code in your development environment. Always verify the publisher's identity, review recent commits, and test in isolated environments before production deployment.
Additional Resources
›View source code on GitHub›Skills CLI documentation›Learn more about Cursor›What are agent skills?