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name
docker-containerization
license
Apache-2.0
description
Write production-grade Dockerfiles, docker-compose configurations, multi-stage builds, and container optimization. Activate on "Dockerfile", "docker", "docker-compose", "container", "multi-stage build", "docker image", "container optimization", "docker security". NOT for Kubernetes orchestration, cloud-specific container services (ECS, Cloud Run), or CI/CD pipelines (use github-actions-pipeline-builder).
allowed-tools
Read,Write,Edit,Bash,Grep,Glob
metadata
{"category":"DevOps & Site Reliability","tags":["docker","containerization","dockerfile","docker-compose"],"pairs-with":[{"skill":"devops-automator","reason":"Docker images are built, tested, and deployed through CI/CD automation pipelines"},{"skill":"github-actions-pipeline-builder","reason":"Container builds and registry pushes are common GitHub Actions workflow stages"},{"skill":"site-reliability-engineer","reason":"Container health checks, resource limits, and orchestration are SRE responsibilities"},{"skill":"microservices-patterns","reason":"Microservices are typically deployed as individual Docker containers"}]}
Write production-grade Dockerfiles with multi-stage builds, security hardening, and size optimization. Covers docker-compose for local development, image layer caching, health checks, and the patterns that separate a 2GB image from a 50MB one.
When to Use
Use for:
Writing Dockerfiles from scratch or improving existing ones
Multi-stage builds for compiled languages (Go, Rust, TypeScript)
Docker Compose for local development environments
Image size optimization (choosing base images, layer caching)
flowchart TD
Start[What are you building?] --> Lang{Language/runtime?}
Lang -->|Node.js/TypeScript| Node[Node pattern]
Lang -->|Python| Python[Python pattern]
Lang -->|Go| Go[Go pattern]
Lang -->|Rust| Rust[Rust pattern]
Lang -->|Static site| Static[Static pattern]
Node --> NQ{Need build step?}
NQ -->|Yes, TypeScript/bundler| MultiNode[Multi-stage: build + runtime]
NQ -->|No, plain JS| SingleNode[Single stage with slim base]
Python --> PQ{Package manager?}
PQ -->|pip| PipPattern[pip + venv pattern]
PQ -->|uv| UvPattern[uv pattern — fastest]
PQ -->|poetry| PoetryPattern[poetry export pattern]
Go --> GoMulti[Multi-stage: build + scratch/distroless]
Rust --> RustMulti[Multi-stage: build + debian-slim]
Static --> StaticMulti[Multi-stage: build + nginx/caddy]
Production Patterns by Language
Node.js / TypeScript (Multi-Stage)
# Stage 1: Dependencies
FROM node:22-alpine AS deps
WORKDIR /app
COPY package.json package-lock.json ./
RUN npm ci --only=production
# Stage 2: Build (TypeScript/bundler)
FROM node:22-alpine AS build
WORKDIR /app
COPY package.json package-lock.json ./
RUN npm ci
COPY . .
RUN npm run build
# Stage 3: Production
FROM node:22-alpine AS production
WORKDIR /app
ENV NODE_ENV=production
# Security: non-root user
RUN addgroup -g 1001 -S nodejs && \
adduser -S nextjs -u 1001
COPY --from=deps /app/node_modules ./node_modules
COPY --from=build /app/dist ./dist
COPY package.json ./
USER nextjs
EXPOSE 3000
HEALTHCHECK --interval=30s --timeout=3s --start-period=5s \
CMD wget -qO- http://localhost:3000/health || exit 1
CMD ["node", "dist/index.js"]
Python (uv — Fastest)
FROM python:3.12-slim AS base
# Install uv
COPY --from=ghcr.io/astral-sh/uv:latest /uv /uvx /bin/
WORKDIR /app
# Install dependencies (cached layer)
COPY pyproject.toml uv.lock ./
RUN uv sync --frozen --no-dev --no-editable
# Copy application code
COPY . .
# Non-root user
RUN useradd -r -s /bin/false appuser
USER appuser
EXPOSE 8000
HEALTHCHECK --interval=30s --timeout=3s \
CMD python -c "import urllib.request; urllib.request.urlopen('http://localhost:8000/health')"
CMD ["uv", "run", "uvicorn", "app.main:app", "--host", "0.0.0.0", "--port", "8000"]
Go (Multi-Stage → Distroless)
# Build stage
FROM golang:1.22-alpine AS build
WORKDIR /app
COPY go.mod go.sum ./
RUN go mod download
COPY . .
RUN CGO_ENABLED=0 GOOS=linux go build -ldflags="-s -w" -o /server ./cmd/server
# Production: distroless (no shell, no package manager, minimal attack surface)
FROM gcr.io/distroless/static-debian12
COPY --from=build /server /server
EXPOSE 8080
USER nonroot:nonroot
ENTRYPOINT ["/server"]
Layer Caching Strategy
flowchart TD
subgraph "Slow to change (cache hit)"
A[Base image] --> B[System packages]
B --> C[Language runtime deps]
end
subgraph "Medium change frequency"
C --> D[Application dependencies]
end
subgraph "Fast changing (cache miss OK)"
D --> E[Application code]
E --> F[Build step]
end
Rule: Order Dockerfile instructions from least-frequently-changed to most-frequently-changed. Each instruction creates a layer. When a layer changes, all subsequent layers are rebuilt.
Anti-Pattern: COPY Before Dependencies
Novice:
COPY . . # ← Busts cache on ANY file change
RUN npm install # ← Reinstalls everything every build
Expert:
COPY package.json package-lock.json ./ # ← Only busts on dependency changes
RUN npm ci # ← Cached when deps unchanged
COPY . . # ← Only app code changes trigger rebuild
Timeline: This has been best practice since Docker layer caching was introduced, but LLMs trained on older tutorials still generate the wrong order.
Docker Compose for Development
# docker-compose.ymlservices:app:build:context:.dockerfile:Dockerfiletarget:development# Use a dev-specific stageports:-"${PORT:-3000}:3000"volumes:-.:/app# Hot reload via bind mount-/app/node_modules# Anonymous volume: don't override node_modulesenvironment:-NODE_ENV=development-DATABASE_URL=postgresql://postgres:postgres@db:5432/myappdepends_on:db:condition:service_healthydevelop:watch:# Docker Compose Watch (2024+)-action:syncpath:./srctarget:/app/src-action:rebuildpath:package.jsondb:image:postgres:16-alpinevolumes:-pgdata:/var/lib/postgresql/dataenvironment:POSTGRES_PASSWORD:postgresPOSTGRES_DB:myapphealthcheck:test: ["CMD-SHELL", "pg_isready -U postgres"]
interval:5stimeout:5sretries:5ports:-"5432:5432"redis:image:redis:7-alpineports:-"6379:6379"healthcheck:test: ["CMD", "redis-cli", "ping"]
interval:5svolumes:pgdata:
Anti-Pattern: No Health Checks
Novice: Relies on depends_on alone — but that only waits for the container to START, not for the service to be READY.
Expert: Always add healthcheck to database/cache services and use condition: service_healthy in depends_on. A Postgres container that has started but hasn't finished WAL recovery will crash your app.
Image Size Optimization
Base Image
Size
Use When
node:22
~1.1 GB
Never in production
node:22-slim
~200 MB
Need apt packages
node:22-alpine
~130 MB
Default choice
distroless
~20 MB
Go/Rust compiled binaries
scratch
0 MB
Fully static binaries
chainguard/*
~10-30 MB
Security-hardened alternatives
Quick Wins
# 1. Use --no-cache for apk/apt
RUN apk add --no-cache curl
# 2. Combine RUN commands to reduce layers
RUN apt-get update && \
apt-get install -y --no-install-recommends curl && \
rm -rf /var/lib/apt/lists/*
# 3. Use .dockerignore aggressively
# .dockerignore:
node_modules
.git
*.md
.env*
dist
coverage
.next
Security Hardening
# 1. Non-root user (MANDATORY)
RUN addgroup -g 1001 -S appgroup && \
adduser -S appuser -u 1001 -G appgroup
USER appuser
# 2. Read-only filesystem (in compose)
# docker-compose.yml:
# read_only: true
# tmpfs:
# - /tmp
# 3. No new privileges
# docker run --security-opt no-new-privileges ...
# 4. Pin image digests for reproducibility
FROM node:22-alpine@sha256:abc123...
# 5. Scan for vulnerabilities
# docker scout quickview myimage:latest
# trivy image myimage:latest
Anti-Pattern: Running as Root
Novice: Skips the USER instruction. Everything runs as root.
Expert: Running as root inside a container means a container escape gives the attacker root on the host. Always create and switch to a non-root user. Only use root for package installation in build stages.
Detection: docker inspect --format='{{.Config.User}}' image:tag — if empty, it's root.
Health Check Strategy by Service Type
Principle: Liveness, Not Readiness
Docker HEALTHCHECK answers one question: "Is this process alive and minimally functional?" It does NOT answer "Are all dependencies reachable?" — that's readiness (a Kubernetes concept). Conflating them causes cascading restarts: DB goes down → every API container "fails" health check → orchestrator restarts them all → thundering herd on DB recovery.
If you need a richer health check for monitoring dashboards (DB status, queue depth, cache hit rate), expose it on /health/detailed and do NOT wire it to Docker HEALTHCHECK.
