docker-optimization

Docker Optimization Patterns

Comprehensive guide to optimizing Docker images for size, build speed, and security. Covers multi-stage builds, layer caching strategies, security hardening, and production deployment patterns.

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Quick Reference

When to use this skill:

• Building production Docker images
• Optimizing image size (reducing from 500MB+ to <100MB)
• Improving Docker build times
• Implementing Docker security best practices
• Debugging slow builds or large images
• Setting up Docker for microservices

Common triggers:

• "My Docker image is too large"
• "Docker builds take forever"
• "How do I optimize this Dockerfile"
• "Docker security best practices"
• "Multi-stage build pattern"

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Part 1: Multi-Stage Builds

The Problem: Bloated Images

Typical single-stage Dockerfile (800MB+ image):

FROM python:3.11
WORKDIR /app
COPY . .
RUN pip install -r requirements.txt
CMD ["python", "app.py"]

Problems:

• Includes build tools (gcc, make, etc.) - 300MB+
• Includes pip cache - 100MB+
• Includes source .git directory - 50MB+
• Includes test files and dev dependencies - 50MB+
• Total: 800MB+ for simple Python app

The Solution: Multi-Stage Pattern

Optimized multi-stage Dockerfile (120MB image):

# Stage 1: Builder
FROM python:3.11-slim AS builder
WORKDIR /app

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

# Copy only requirements first (cache optimization)
COPY requirements.txt .
RUN pip install --user --no-cache-dir -r requirements.txt

# Stage 2: Runtime
FROM python:3.11-slim
WORKDIR /app

# Copy only Python packages from builder
COPY --from=builder /root/.local /root/.local

# Copy only application code
COPY app.py .
COPY src/ ./src/

# Make sure scripts in .local are usable
ENV PATH=/root/.local/bin:$PATH

# Run as non-root user
RUN useradd -m appuser && chown -R appuser:appuser /app
USER appuser

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