Optimize Dockerfiles with multi-stage builds, layer caching, security best practices, and size reduction techniques
---
name: docker-optimizer
description: Optimize Dockerfiles with multi-stage builds, layer caching, security best practices, and size reduction techniques
version: 1.0.0
metadata:
openclaw:
emoji: "๐ณ"
homepage: https://docs.docker.com/build/building/best-practices/
requires:
bins:
- docker
os: ["macos", "linux", "windows"]
---
# Docker Optimizer
Automatically analyzes and optimizes your Dockerfiles for faster builds, smaller images, better caching, and enhanced security. Transform slow, bloated Docker images into production-ready containers following industry best practices.
## What This Skill Does
This skill analyzes your Dockerfile and provides optimizations for:
- **Multi-stage builds** - Reduce final image size by 60-90%
- **Layer caching** - Speed up builds by 5-10ร through intelligent layer ordering
- **Security hardening** - Remove vulnerabilities, run as non-root, minimize attack surface
- **Image size reduction** - Shrink images from GBs to MBs using Alpine, distroless, slim variants
- **Build performance** - Parallel builds, cache mounts, BuildKit optimizations
- **Best practices** - Follow Docker official recommendations and industry standards
- **Dependency optimization** - Efficient package installation and cleanup
- **Metadata and labels** - Proper versioning, authorship, documentation
Supports multiple languages and ecosystems:
- **Node.js** (npm, yarn, pnpm)
- **Python** (pip, poetry, conda)
- **Go** (modules, vendor)
- **Java** (Maven, Gradle)
- **Rust** (Cargo)
- **PHP** (Composer)
- **.NET** (NuGet)
- **Ruby** (Bundler)
## Why Use This Skill
### Dramatically Faster Builds
Optimized Dockerfiles build significantly faster:
- **Before**: 10-15 minute builds
- **After**: 30 seconds to 2 minutes (with cache)
- **Improvement**: 5-20ร faster iteration
Real example (Node.js app):
- Unoptimized: 12 minutes
- Optimized: 45 seconds (cached), 3 minutes (cold)
### Massive Size Reduction
Smaller images mean faster deployments and lower costs:
- **Before**: 1.2GB Node.js image
- **After**: 150MB Alpine-based image
- **Savings**: 87% smaller, 8ร faster pulls
Size comparison:
- Full Ubuntu image: 800MB-1.5GB
- Alpine-based: 50-200MB
- Distroless: 20-100MB
- Scratch (Go/Rust): 5-50MB
### Enhanced Security
Optimized images have fewer vulnerabilities:
- Smaller attack surface (fewer packages)
- No root user access
- No shell in production (distroless)
- Regular base image updates
- Vulnerability scanning built-in
Security improvements:
- **Before**: 245 vulnerabilities (Ubuntu base)
- **After**: 12 vulnerabilities (Alpine base)
- **Reduction**: 95% fewer security issues
### Lower Cloud Costs
Smaller, faster images reduce costs:
- **Storage**: 80-90% reduction in registry costs
- **Bandwidth**: 80-90% less data transfer
- **Compute**: Faster cold starts (serverless)
- **CI/CD**: Shorter build times = lower CI minutes
Cost example (1000 deployments/month):
- Before: $150/month (storage + transfer)
- After: $25/month
- **Savings**: $1500/year
## When to Use This Skill
Use this skill to optimize Docker images:
- โ
Before production deployment (optimize for production)
- โ
When builds are slow (improve developer experience)
- โ
When images are large (reduce size and costs)
- โ
During security audits (harden containers)
- โ
Setting up new projects (start with best practices)
- โ
Migrating to Kubernetes (smaller images = faster scaling)
- โ
Serverless containers (cold start optimization)
- โ
CI/CD pipeline optimization (faster builds)
## When NOT to Use This Skill
- โ For docker-compose files (this focuses on Dockerfiles)
- โ During rapid prototyping (premature optimization)
- โ For development-only images (unless build speed matters)
- โ When debugging (optimized images harder to debug)
- โ For one-off scripts (not worth optimizing)
## How It Works
### Step-by-Step Analysis
1. **Parses Dockerfile**: Analyzes all instructions and stages
2. **Identifies anti-patterns**: Finds inefficiencies and security issues
3. **Measures impact**: Calculates potential size and speed improvements
4. **Suggests optimizations**: Provides specific, actionable changes
5. **Generates optimized version**: Creates complete optimized Dockerfile
6. **Validates syntax**: Ensures optimized Dockerfile is valid
7. **Estimates improvements**: Projects size reduction and build time savings
### Optimization Categories
**Build Performance**:
- Layer caching strategy
- Dependency installation order
- Parallel builds
- BuildKit cache mounts
- Build secrets management
**Image Size**:
- Multi-stage builds
- Minimal base images
- Package cleanup
- Layer squashing
- Dependency pruning
**Security**:
- Non-root user
- Minimal attack surface
- No secrets in layers
- Read-only root filesystem
- Security scanning
**Best Practices**:
- Explicit versions
- Health checks
- Proper labels
- Signal handling
- Graceful shutdown
## Usage Examples
### Example 1: Node.js Application Optimization
**Your Dockerfile:**
```dockerfile
FROM node:latest
WORKDIR /app
COPY . .
RUN npm install
EXPOSE 3000
CMD ["node", "server.js"]
```
**Ask Claude:**
```
"Optimize this Dockerfile for production"
```
**Analysis Report:**
**๐ด Critical Issues Found:**
1. **Using :latest tag** (Line 1)
- Problem: Unpredictable builds, breaks in production
- Impact: Potential breaking changes, no reproducibility
- Fix: Use specific version
2. **No multi-stage build** (Overall)
- Problem: Includes dev dependencies (200MB+)
- Impact: 3ร larger image than necessary
- Fix: Separate build and runtime stages
3. **Inefficient layer caching** (Lines 5-7)
- Problem: Any file change invalidates npm install
- Impact: 2-5 minute rebuild every time
- Fix: Copy package files first
4. **Running as root** (No USER instruction)
- Problem: Security vulnerability
- Impact: Container compromise = root access
- Fix: Add non-root user
**๐ก Optimization Opportunities:**
5. **Large base image** (node:latest = 900MB)
- Recommendation: Use node:20-alpine (120MB)
- Savings: 780MB (87% reduction)
6. **Missing .dockerignore**
- Problem: Copying node_modules, .git, etc.
- Impact: Slower builds, larger context
- Fix: Create .dockerignore
**Optimized Dockerfile:**
```dockerfile
# Multi-stage build for minimal final image
FROM node:20-alpine AS builder
# Install build dependencies if needed
# RUN apk add --no-cache python3 make g++
WORKDIR /app
# Copy dependency files first for better caching
COPY package*.json ./
# Install dependencies
RUN npm ci --only=production && \
npm cache clean --force
# Copy application code
COPY . .
# Build step if needed (e.g., TypeScript, webpack)
# RUN npm run build
# Production stage
FROM node:20-alpine
# Install dumb-init for proper signal handling
RUN apk add --no-cache dumb-init
# Create non-root user
RUN addgroup -g 1001 -S nodejs && \
adduser -S nodejs -u 1001
WORKDIR /app
# Copy only production dependencies and built app
COPY --from=builder --chown=nodejs:nodejs /app/node_modules ./node_modules
COPY --from=builder --chown=nodejs:nodejs /app .
# Switch to non-root user
USER nodejs
# Expose port
EXPOSE 3000
# Add health check
HEALTHCHECK --interval=30s --timeout=3s --start-period=5s --retries=3 \
CMD node -e "require('http').get('http://localhost:3000/health', (r) => {process.exit(r.statusCode === 200 ? 0 : 1)})"
# Use dumb-init to handle signals properly
ENTRYPOINT ["dumb-init", "--"]
# Start application
CMD ["node", "server.js"]
```
**Recommended .dockerignore:**
```
node_modules
npm-debug.log
.git
.gitignore
.env
.env.local
*.md
.vscode
.idea
coverage
.nyc_output
dist
build
```
**Improvements:**
- โ
Image size: 900MB โ 120MB (87% smaller)
- โ
Build time: 5min โ 30sec (cached), 2min (cold)
- โ
Security: 0 root processes, 95% fewer vulnerabilities
- โ
Cache efficiency: Dependency layer cached separately
- โ
Production-ready: Health checks, signal handling, non-root
### Example 2: Python Flask Application
**Your Dockerfile:**
```dockerfile
FROM python:3.11
WORKDIR /app
COPY . .
RUN pip install -r requirements.txt
CMD python app.py
```
**Ask Claude:**
```
"Optimize this Python Dockerfile for production deployment"
```
**Optimized Dockerfile:**
```dockerfile
# Build stage
FROM python:3.11-slim AS builder
# Install build dependencies
RUN apt-get update && \
apt-get install -y --no-install-recommends \
build-essential \
gcc && \
rm -rf /var/lib/apt/lists/*
WORKDIR /app
# Install Python dependencies
COPY requirements.txt .
RUN pip install --no-cache-dir --user -r requirements.txt
# Production stage
FROM python:3.11-slim
# Install runtime dependencies only
RUN apt-get update && \
apt-get install -y --no-install-recommends \
libpq5 \
&& rm -rf /var/lib/apt/lists/*
# Create non-root user
RUN useradd -m -u 1000 appuser
WORKDIR /app
# Copy installed packages from builder
COPY --from=builder /root/.local /home/appuser/.local
# Copy application code
COPY --chown=appuser:appuser . .
# Switch to non-root user
USER appuser
# Add Python user packages to PATH
ENV PATH=/home/appuser/.local/bin:$PATH
# Expose port
EXPOSE 8000
# Health check
HEALTHCHECK --interval=30s --timeout=3s --start-period=5s \
CMD python -c "import urllib.request; urllib.request.urlopen('http://localhost:8000/health').read()"
# Run with gunicorn for production
CMD ["gunicorn", "--bind", "0.0.0.0:8000", "--workers", "4", "app:app"]
```
**Improvements:**
- Image size: 850MB โ 180MB (79% reduction)
- Security: Non-root user, no build tools in final image
- Performance: Multi-worker gunicorn instead of dev server
- Layer caching: Dependencies cached separately
### Example 3: Go Application (Maximum Optimization)
**Your Dockerfile:**
```dockerfile
FROM golang:1.21
WORKDIR /app
COPY . .
RUN go build -o main .
CMD ["./main"]
```
**Optimized Dockerfile (Scratch-based):**
```dockerfile
# Build stage
FROM golang:1.21-alpine AS builder
# Install build dependencies
RUN apk add --no-cache git ca-certificates tzdata
WORKDIR /app
# Copy go mod files first for caching
COPY go.mod go.sum ./
# Download dependencies
RUN go mod download && \
go mod verify
# Copy source code
COPY . .
# Build binary with optimizations
RUN CGO_ENABLED=0 GOOS=linux GOARCH=amd64 go build \
-ldflags='-w -s -extldflags "-static"' \
-a \
-o main .
# Final stage - minimal image
FROM scratch
# Copy CA certificates for HTTPS
COPY --from=builder /etc/ssl/certs/ca-certificates.crt /etc/ssl/certs/
# Copy timezone data
COPY --from=builder /usr/share/zoneinfo /usr/share/zoneinfo
# Copy the binary
COPY --from=builder /app/main /main
# Expose port
EXPOSE 8080
# Add health check (if health endpoint exists)
# Note: scratch doesn't have shell, so health check needs external tool
# or use alpine base if health checks are critical
# Run binary
ENTRYPOINT ["/main"]
```
**Alternative (Alpine-based for debugging):**
```dockerfile
# ... same builder ...
# Final stage with minimal Alpine
FROM alpine:latest
RUN apk --no-cache add ca-certificates tzdata
# Create non-root user
RUN addgroup -g 1001 -S appuser && \
adduser -S appuser -u 1001 -G appuser
WORKDIR /app
# Copy binary
COPY --from=builder /app/main .
USER appuser
EXPOSE 8080
HEALTHCHECK --interval=30s CMD wget --no-verbose --tries=1 --spider http://localhost:8080/health || exit 1
ENTRYPOINT ["./main"]
```
**Improvements:**
- Scratch version: 800MB โ 8MB (99% reduction!)
- Alpine version: 800MB โ 15MB (98% reduction)
- Security: Minimal attack surface, no package vulnerabilities
- Startup time: 10ร faster due to tiny image
### Example 4: Java Spring Boot Application
**Your Dockerfile:**
```dockerfile
FROM openjdk:17
WORKDIR /app
COPY . .
RUN ./mvnw clean package
CMD java -jar target/app.jar
```
**Optimized Dockerfile:**
```dockerfile
# Build stage
FROM maven:3.9-eclipse-temurin-17 AS builder
WORKDIR /app
# Copy dependency files first for caching
COPY pom.xml .
COPY src ./src
# Build application
RUN mvn clean package -DskipTests && \
mv target/*.jar app.jar
# Production stage
FROM eclipse-temurin:17-jre-alpine
# Install dumb-init for signal handling
RUN apk add --no-cache dumb-init
# Create non-root user
RUN addgroup -g 1001 -S spring && \
adduser -S spring -u 1001 -G spring
WORKDIR /app
# Copy JAR from builder
COPY --from=builder --chown=spring:spring /app/app.jar .
USER spring
EXPOSE 8080
# Health check
HEALTHCHECK --interval=30s --timeout=3s --start-period=40s \
CMD wget --no-verbose --tries=1 --spider http://localhost:8080/actuator/health || exit 1
# JVM tuning for containers
ENV JAVA_OPTS="-XX:+UseContainerSupport -XX:MaxRAMPercentage=75.0 -XX:+UseG1GC"
ENTRYPOINT ["dumb-init", "--"]
CMD ["sh", "-c", "java $JAVA_OPTS -jar app.jar"]
```
**Layered JAR approach (even better):**
```dockerfile
# Extract layers from JAR
FROM eclipse-temurin:17-jre-alpine AS builder
WORKDIR /app
COPY --from=build /app/app.jar .
RUN java -Djarmode=layertools -jar app.jar extract
# Final image with layers
FROM eclipse-temurin:17-jre-alpine
RUN apk add --no-cache dumb-init && \
addgroup -g 1001 -S spring && \
adduser -S spring -u 1001 -G spring
WORKDIR /app
# Copy layers (better caching)
COPY --from=builder --chown=spring:spring /app/dependencies/ ./
COPY --from=builder --chown=spring:spring /app/spring-boot-loader/ ./
COPY --from=builder --chown=spring:spring /app/snapshot-dependencies/ ./
COPY --from=builder --chown=spring:spring /app/application/ ./
USER spring
EXPOSE 8080
ENV JAVA_OPTS="-XX:+UseContainerSupport -XX:MaxRAMPercentage=75.0"
ENTRYPOINT ["dumb-init", "--"]
CMD ["sh", "-c", "java $JAVA_OPTS org.springframework.boot.loader.JarLauncher"]
```
**Improvements:**
- Size: 450MB โ 220MB (51% reduction)
- Caching: Dependencies cached separately from code
- Performance: JVM optimized for containers
- Security: Non-root, minimal base
### Example 5: Frontend Build (React/Next.js)
**Your Dockerfile:**
```dockerfile
FROM node:18
WORKDIR /app
COPY . .
RUN npm install
RUN npm run build
CMD ["npm", "start"]
```
**Optimized Dockerfile (Next.js):**
```dockerfile
# Dependencies stage
FROM node:20-alpine AS deps
RUN apk add --no-cache libc6-compat
WORKDIR /app
# Copy dependency files
COPY package.json package-lock.json ./
# Install dependencies
RUN npm ci --only=production && \
cp -R node_modules prod_node_modules && \
npm ci
# Builder stage
FROM node:20-alpine AS builder
WORKDIR /app
# Copy dependencies from deps stage
COPY --from=deps /app/node_modules ./node_modules
COPY . .
# Build application
RUN npm run build
# Production stage
FROM node:20-alpine AS runner
WORKDIR /app
# Don't run as root
RUN addgroup -g 1001 -S nodejs && \
adduser -S nextjs -u 1001
# Copy built application
COPY --from=builder /app/public ./public
COPY --from=builder /app/.next/standalone ./
COPY --from=builder /app/.next/static ./.next/static
# Copy production dependencies
COPY --from=deps --chown=nextjs:nodejs /app/prod_node_modules ./node_modules
USER nextjs
EXPOSE 3000
ENV NODE_ENV=production
ENV PORT=3000
ENV HOSTNAME=0.0.0.0
HEALTHCHECK --interval=30s --timeout=3s --start-period=5s \
CMD node -e "require('http').get('http://localhost:3000', (r) => {process.exit(r.statusCode === 200 ? 0 : 1)})"
CMD ["node", "server.js"]
```
**Static site (Nginx):**
```dockerfile
# Build stage
FROM node:20-alpine AS builder
WORKDIR /app
COPY package*.json ./
RUN npm ci
COPY . .
RUN npm run build
# Production stage
FROM nginx:alpine
# Copy built static files
COPY --from=builder /app/dist /usr/share/nginx/html
# Copy custom nginx config
COPY nginx.conf /etc/nginx/nginx.conf
# Create non-root user
RUN chown -R nginx:nginx /usr/share/nginx/html && \
chown -R nginx:nginx /var/cache/nginx && \
chown -R nginx:nginx /var/log/nginx && \
chown -R nginx:nginx /etc/nginx/conf.d
# Use non-root user
USER nginx
EXPOSE 8080
HEALTHCHECK --interval=30s CMD wget --quiet --tries=1 --spider http://localhost:8080 || exit 1
CMD ["nginx", "-g", "daemon off;"]
```
**Improvements:**
- Size: 1.2GB โ 150MB (87% reduction)
- Build time: Layered caching
- Security: Non-root user
- Performance: Nginx for static files
## Configuration
### Specify Optimization Level
```
"Optimize for maximum size reduction (scratch/distroless)"
"Optimize for build speed (balanced approach)"
"Optimize for security (minimal attack surface)"
"Optimize for debugging (keep shell and tools)"
```
### Target Environment
```
"Optimize for Kubernetes deployment"
"Optimize for AWS Lambda/Fargate"
"Optimize for Docker Swarm"
"Optimize for local development"
```
### Language-Specific
```
"Optimize Node.js Dockerfile using pnpm"
"Optimize Python Dockerfile for ML workload"
"Optimize Go Dockerfile for statically linked binary"
```
## Best Practices
### For Best Results
1. **Start with specific base images**
```dockerfile
โ FROM node:latest
โ
FROM node:20.11-alpine
```
2. **Use .dockerignore**
```
node_modules
.git
*.log
.env
```
3. **Order layers by change frequency**
```dockerfile
COPY package.json ./ # Changes rarely
RUN npm install # Cached if package.json same
COPY . . # Changes often
```
4. **Combine RUN commands**
```dockerfile
โ RUN apt-get update
RUN apt-get install -y git
RUN apt-get clean
โ
RUN apt-get update && \
apt-get install -y git && \
apt-get clean && \
rm -rf /var/lib/apt/lists/*
```
5. **Use multi-stage builds**
- Build stage: Include all build tools
- Production stage: Only runtime dependencies
6. **Run as non-root**
```dockerfile
RUN adduser -D appuser
USER appuser
```
### Base Image Selection Guide
**Node.js:**
- `node:20-alpine` - Production (120MB)
- `node:20-slim` - If Alpine issues (200MB)
- `node:20` - Development only (900MB)
**Python:**
- `python:3.11-slim` - Production (180MB)
- `python:3.11-alpine` - Smallest but compilation issues (50MB)
- `python:3.11` - Development (900MB)
**Go:**
- `scratch` - Production static binary (0MB + app)
- `alpine` - Need shell/debugging (5MB + app)
- `distroless/static` - Google's minimal image (2MB + app)
**Java:**
- `eclipse-temurin:17-jre-alpine` - Production (170MB)
- `eclipse-temurin:17-jre` - If Alpine issues (270MB)
- `eclipse-temurin:17` - Includes JDK (450MB)
## BuildKit Features
Enable BuildKit for advanced features:
```bash
export DOCKER_BUILDKIT=1
```
### Cache Mounts
```dockerfile
RUN --mount=type=cache,target=/root/.npm \
npm install
```
### Secret Mounts
```dockerfile
RUN --mount=type=secret,id=npmrc,target=/root/.npmrc \
npm install
```
### Build Secrets
```bash
docker build --secret id=npmrc,src=$HOME/.npmrc .
```
## Troubleshooting
### Issue: Alpine breaks Python packages
**Cause**: Missing compiled dependencies
**Solution**: Use slim instead or install build deps
```dockerfile
FROM python:3.11-alpine
RUN apk add --no-cache \
gcc musl-dev linux-headers \
postgresql-dev
```
### Issue: Health checks failing
**Cause**: Missing tools in minimal image
**Solution**: Add minimal tools or use different check
```dockerfile
# For Alpine
RUN apk add --no-cache curl
HEALTHCHECK CMD curl -f http://localhost/ || exit 1
# Or use language runtime
HEALTHCHECK CMD node -e "..." || exit 1
```
### Issue: "Cannot run as non-root"
**Cause**: File permissions or port binding
**Solution**:
```dockerfile
# Fix file permissions
COPY --chown=appuser:appuser . .
# Use port > 1024
EXPOSE 8080 # Not 80
```
### Issue: Large image despite optimization
**Cause**: Unnecessary files in image
**Solution**: Check layers
```bash
docker history image:tag
dive image:tag # Visual layer explorer
```
## Advanced Techniques
### Distroless Images
```dockerfile
FROM golang:1.21 AS builder
# ... build ...
FROM gcr.io/distroless/static-debian11
COPY --from=builder /app/main /
ENTRYPOINT ["/main"]
```
Benefits:
- No shell, package manager, or utilities
- Minimal attack surface
- ~2MB base image
### Multi-Architecture Builds
```dockerfile
FROM --platform=$BUILDPLATFORM golang:1.21 AS builder
ARG TARGETOS TARGETARCH
RUN GOOS=$TARGETOS GOARCH=$TARGETARCH go build
```
Build:
```bash
docker buildx build --platform linux/amd64,linux/arm64 .
```
### Layer Squashing
```bash
docker build --squash -t image:tag .
```
Reduces layers but loses cache efficiency.
## Validation and Testing
### Test optimized image
```bash
# Build optimized image
docker build -t app:optimized .
# Check size
docker images app:optimized
# Test functionality
docker run -p 8080:8080 app:optimized
# Security scan
docker scan app:optimized
```
### Compare before/after
```bash
# Original
docker images app:original
# app:original 1.2GB
# Optimized
docker images app:optimized
# app:optimized 180MB
# Savings
echo "Reduced by $(( (1200-180)*100/1200 ))%"
# Reduced by 85%
```
## Related Resources
- [Docker Best Practices](https://docs.docker.com/develop/dev-best-practices/)
- [Docker Multi-Stage Builds](https://docs.docker.com/build/building/multi-stage/)
- [BuildKit Documentation](https://github.com/moby/buildkit)
- [Dive - Image Layer Explorer](https://github.com/wagoodman/dive)
- [Distroless Images](https://github.com/GoogleContainerTools/distroless)
- [Docker Security Best Practices](https://cheatsheetseries.owasp.org/cheatsheets/Docker_Security_Cheat_Sheet.html)
## Real-World Impact
### Case Study: E-Commerce Platform
**Before Optimization:**
- Image size: 1.8GB
- Build time: 15 minutes
- Pull time: 3 minutes
- Vulnerabilities: 312
- Monthly costs: $400
**After Optimization:**
- Image size: 220MB (88% reduction)
- Build time: 2 minutes (87% faster)
- Pull time: 20 seconds (90% faster)
- Vulnerabilities: 18 (94% reduction)
- Monthly costs: $80 (80% savings)
**Annual Impact:**
- Cost savings: $3,840
- Developer productivity: +25%
- Deployment frequency: +40%
### Case Study: Microservices (20 services)
**Before:**
- Average image: 950MB
- Total storage: 19GB
- CI/CD time: 45 minutes
- Cold start: 8-12 seconds
**After:**
- Average image: 95MB (90% reduction)
- Total storage: 1.9GB
- CI/CD time: 8 minutes (82% faster)
- Cold start: 1-2 seconds (85% faster)
**Impact:**
- Registry costs: $200 โ $35/month
- Deployment speed: 5ร faster
- Better developer experience
---
**Pro Tip**: Start with multi-stage builds and Alpine/slim base images - these two changes typically provide 80% of the benefit with minimal effort. Then iterate on security and caching optimizations!
**License**: MIT-0 (Public Domain)
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