Docker

Docker

Container optimization, security hardening, multi-stage builds, and production deployment patterns.

Installation

OpenClaw / Moltbot / Clawbot

npx clawhub@latest install docker

NEVER

• NEVER use :latest tag - Always use specific version tags for reproducibility
• NEVER run as root - Create and use non-root users with specific UID/GID
• NEVER store secrets in images - Use Docker secrets, env vars at runtime, or secret managers
• NEVER skip .dockerignore - Always create comprehensive .dockerignore to reduce build context
• NEVER install dev dependencies in production - Use multi-stage builds to separate concerns
• NEVER leave package manager caches - Clean in the same RUN layer (npm ci && npm cache clean --force)
• NEVER use docker-compose (v1) - Use docker compose (v2) with plugin syntax

Quick Reference

Multi-Stage Build Pattern

# Stage 1: Dependencies
FROM node:20-alpine AS deps
WORKDIR /app
COPY package*.json ./
RUN npm ci --only=production && npm cache clean --force

# Stage 2: Build
FROM node:20-alpine AS build
WORKDIR /app
COPY package*.json ./
RUN npm ci
COPY . .
RUN npm run build && npm prune --production

# Stage 3: Production
FROM node:20-alpine AS runtime
RUN addgroup -g 1001 -S nodejs && adduser -S app -u 1001
WORKDIR /app
COPY --from=deps --chown=app:nodejs /app/node_modules ./node_modules
COPY --from=build --chown=app:nodejs /app/dist ./dist
COPY --from=build --chown=app:nodejs /app/package*.json ./

USER app
EXPOSE 3000

HEALTHCHECK --interval=30s --timeout=10s --start-period=5s --retries=3 \
  CMD wget --no-verbose --tries=1 --spider http://localhost:3000/health || exit 1

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

Security-Hardened Container

FROM node:20-alpine

# Create non-root user with specific UID/GID
RUN addgroup -g 1001 -S appgroup && \
    adduser -S appuser -u 1001 -G appgroup

WORKDIR /app

# Copy with ownership
COPY --chown=appuser:appgroup package*.json ./
RUN npm ci --only=production && npm cache clean --force
COPY --chown=appuser:appgroup . .

# Switch to non-root user
USER 1001

# At runtime: --cap-drop=ALL --read-only --security-opt=no-new-privileges

Production Docker Compose

services:
  app:
    build:
      context: .
      target: production
    depends_on:
      db:
        condition: service_healthy
    networks:
      - frontend
      - backend
    healthcheck:
      test: ["CMD", "wget", "--spider", "-q", "http://localhost:3000/health"]
      interval: 30s
      timeout: 10s
      retries: 3
      start_period: 40s
    deploy:
      resources:
        limits:
          cpus: '0.5'
          memory: 512M
        reservations:
          cpus: '0.25'
          memory: 256M
    restart: unless-stopped

  db:
    image: postgres:16-alpine
    environment:
      POSTGRES_DB_FILE: /run/secrets/db_name
      POSTGRES_USER_FILE: /run/secrets/db_user
      POSTGRES_PASSWORD_FILE: /run/secrets/db_password
    secrets:
      - db_name
      - db_user
      - db_password
    volumes:
      - postgres_data:/var/lib/postgresql/data
    networks:
      - backend
    healthcheck:
      test: ["CMD-SHELL", "pg_isready -U postgres"]
      interval: 10s
      timeout: 5s
      retries: 5

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

volumes:
  postgres_data:

secrets:
  db_name:
    file: ./secrets/db_name.txt
  db_user:
    file: ./secrets/db_user.txt
  db_password:
    file: ./secrets/db_password.txt

.dockerignore Template

# Dependencies
node_modules
.pnpm-store

# Build outputs
dist
build
.next
out

# Development
.git
.gitignore
*.md
LICENSE
docs/

# IDE
.vscode
.idea
*.swp
*.swo

# Testing
coverage
.nyc_output
*.test.js
*.spec.js
__tests__

# Environment
.env*
!.env.example

# Docker
Dockerfile*
docker-compose*
.docker

# Misc
.DS_Store
*.log
tmp

Common Patterns

Build Cache Optimization

# Mount build cache for faster rebuilds
FROM node:20-alpine AS deps
WORKDIR /app
COPY package*.json ./
RUN --mount=type=cache,target=/root/.npm \
    npm ci --only=production

Build-Time Secrets

# BuildKit secrets (never stored in image layers)
FROM alpine
RUN --mount=type=secret,id=api_key \
    API_KEY=$(cat /run/secrets/api_key) && \
    # Use API_KEY for build process
    echo "Key loaded"

# Build with secret
docker build --secret id=api_key,src=./api_key.txt .

Multi-Architecture Builds

# Create builder for multi-arch
docker buildx create --name multiarch --use

# Build for multiple platforms
docker buildx build --platform linux/amd64,linux/arm64 \
  -t myapp:latest --push .

Development Override

# docker-compose.override.yml (auto-loaded in dev)
services:
  app:
    build:
      target: development
    volumes:
      - .:/app
      - /app/node_modules  # Anonymous volume for node_modules
    environment:
      - NODE_ENV=development
      - DEBUG=app:*
    ports:
      - "9229:9229"  # Debug port
    command: npm run dev

Framework-Specific Patterns

Next.js Production

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

FROM node:20-alpine AS builder
WORKDIR /app
COPY --from=deps /app/node_modules ./node_modules
COPY . .
ENV NEXT_TELEMETRY_DISABLED=1
RUN npm run build

FROM node:20-alpine 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"]

Python FastAPI

FROM python:3.12-slim AS base
ENV PYTHONDONTWRITEBYTECODE=1 \
    PYTHONUNBUFFERED=1 \
    PIP_NO_CACHE_DIR=1

FROM base AS deps
WORKDIR /app
COPY requirements.txt .
RUN pip install --no-cache-dir -r requirements.txt

FROM base AS runtime
WORKDIR /app
RUN useradd -m -u 1001 appuser
COPY --from=deps /usr/local/lib/python3.12/site-packages /usr/local/lib/python3.12/site-packages
COPY --chown=appuser:appuser . .

USER appuser
EXPOSE 8000
CMD ["uvicorn", "main:app", "--host", "0.0.0.0", "--port", "8000"]

Go Distroless

FROM golang:1.22-alpine AS builder
WORKDIR /app
COPY go.mod go.sum ./
RUN go mod download
COPY . .
RUN CGO_ENABLED=0 GOOS=linux go build -ldflags="-s -w" -o /app/server

FROM gcr.io/distroless/static-debian12
COPY --from=builder /app/server /server
USER nonroot:nonroot
EXPOSE 8080
ENTRYPOINT ["/server"]

Troubleshooting

Image Size Issues

# Analyze layers
docker history myapp:latest --no-trunc

# Use dive for detailed analysis
dive myapp:latest

# Check actual size
docker images myapp --format "{{.Size}}"

Common causes:

• Dev dependencies in production → Use npm ci --only=production
• Large base images → Use Alpine or distroless
• Uncleaned caches → Clean in same RUN layer
• Unnecessary files → Improve .dockerignore

Build Performance

# Enable BuildKit (faster, better caching)
export DOCKER_BUILDKIT=1

# Build with cache export
docker build --cache-from myapp:latest -t myapp:new .

# Check build cache
docker buildx du

Debugging Containers

# Shell into running container
docker exec -it <container> sh

# Shell into failed container
docker run -it --entrypoint sh myapp:latest

# Check container logs
docker logs -f <container>

# Inspect container details
docker inspect <container>

Review Checklist

Dockerfile

• Multi-stage build separates build/runtime
• Dependencies copied before source (layer caching)
• Specific base image tags (no :latest)
• Non-root user with specific UID/GID
• Package cache cleaned in same RUN layer
• Health check configured
• .dockerignore is comprehensive

Security

• Runs as non-root user
• No secrets in image layers
• Minimal base image (Alpine/distroless)
• Read-only filesystem where possible
• Capabilities dropped at runtime

Docker Compose

• Health checks with condition: service_healthy
• Resource limits defined
• Internal networks for backend services
• Secrets via files, not environment
• Restart policy configured