Docker Optimization Skill

Comprehensive optimization techniques for Docker images and containers covering size reduction, build caching, and runtime performance.

Purpose

Reduce image size, improve build times, and optimize container performance using 2024-2025 industry best practices.

Parameters

Parameter	Type	Required	Default	Description
target	enum	No	all	size/build/runtime/all
base_image	string	No	-	Current base image
current_size	string	No	-	Current image size

Optimization Strategies

1. Image Size Reduction

Base Image Selection

Base	Size	Use Case
scratch	0	Static Go/Rust binaries
distroless	2-20MB	Production containers
alpine	5MB	General purpose
slim	80-150MB	When apt packages needed
full	500MB+	Development only

# Before: 1.2GB
FROM node:20

# After: 150MB (88% smaller)
FROM node:20-alpine

Layer Optimization

# Bad: 3 layers, 150MB
RUN apt-get update
RUN apt-get install -y curl
RUN rm -rf /var/lib/apt/lists/*

# Good: 1 layer, 50MB
RUN apt-get update && \
    apt-get install -y --no-install-recommends curl && \
    rm -rf /var/lib/apt/lists/*

Remove Unnecessary Files

# Clean package manager cache
RUN npm cache clean --force
RUN pip cache purge
RUN apt-get clean && rm -rf /var/lib/apt/lists/*

# Use .dockerignore
# node_modules, .git, *.md, tests/, docs/

2. Build Speed Optimization

Layer Caching Strategy

# Dependencies first (rarely change)
COPY package*.json ./
RUN npm ci

# Source code last (frequently changes)
COPY . .
RUN npm run build

BuildKit Cache Mounts

# syntax=docker/dockerfile:1
FROM node:20-alpine

# Cache npm packages
RUN --mount=type=cache,target=/root/.npm \
    npm ci

# Cache pip packages
RUN --mount=type=cache,target=/root/.cache/pip \
    pip install -r requirements.txt

Parallel Multi-Stage

# Parallel stages (BuildKit)
FROM node:20-alpine AS deps
COPY package*.json ./
RUN npm ci

FROM deps AS builder
COPY . .
RUN npm run build

FROM deps AS linter
COPY . .
RUN npm run lint

3. Runtime Performance

Resource Limits

services:
  app:
    deploy:
      resources:
        limits:
          cpus: '1'
          memory: 512M
        reservations:
          cpus: '0.5'
          memory: 256M

Container Tuning

# Set memory limits
docker run --memory=512m --memory-swap=512m app

# CPU limits
docker run --cpus=1.5 app

# I/O limits
docker run --device-read-bps=/dev/sda:1mb app

Optimization Checklist

Size Checklist

• Using smallest viable base image?
• Multi-stage build implemented?
• Package manager cache cleaned?
• Dev dependencies excluded?
• .dockerignore configured?

Build Speed Checklist

• Dependencies copied before code?
• BuildKit enabled?
• Cache mounts used?
• Parallel stages where possible?

Runtime Checklist

• Resource limits set?
• Health checks configured?
• Non-root user?
• Read-only filesystem where possible?

Analysis Tools

# Image size analysis
docker images --format "table {{.Repository}}\t{{.Tag}}\t{{.Size}}"

# Layer analysis
docker history <image> --format "{{.Size}}\t{{.CreatedBy}}"

# Deep dive analysis
dive <image>

# Build time analysis
DOCKER_BUILDKIT=1 docker build --progress=plain .

Error Handling

Common Issues

Issue	Cause	Solution
Large image	No multi-stage	Implement multi-stage
Slow builds	Poor layer order	Dependencies before code
Cache not working	Context changes	Use .dockerignore
OOM at runtime	No limits	Set memory limits

Troubleshooting

Debug Checklist

• BuildKit enabled? (DOCKER_BUILDKIT=1)
• Cache being used? (Check build output)
• .dockerignore working? (Check context size)
• Layers optimized? (Run dive)

Usage

Skill("docker-optimization")

Related Skills

• docker-multi-stage
• dockerfile-basics
• docker-production