docker-development – DevOps & Infrastructure skill for AI agents

Docker Development

> Smaller images. Faster builds. Secure containers. No guesswork.

Opinionated Docker workflow that turns bloated Dockerfiles into production-grade containers. Covers optimization, multi-stage builds, compose orchestration, and security hardening.

Not a Docker tutorial — a set of concrete decisions about how to build containers that don't waste time, space, or attack surface.

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Slash Commands

| Command | What it does |

|---------|-------------|

| /docker:optimize | Analyze and optimize a Dockerfile for size, speed, and layer caching |

| /docker:compose | Generate or improve docker-compose.yml with best practices |

| /docker:security | Audit a Dockerfile or running container for security issues |

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When This Skill Activates

Recognize these patterns from the user:

• "Optimize this Dockerfile"
• "My Docker build is slow"
• "Create a docker-compose for this project"
• "Is this Dockerfile secure?"
• "Reduce my Docker image size"
• "Set up multi-stage builds"
• "Docker best practices for [language/framework]"
• Any request involving: Dockerfile, docker-compose, container, image size, build cache, Docker security

If the user has a Dockerfile or wants to containerize something → this skill applies.

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Workflow

/docker:optimize — Dockerfile Optimization

1. Analyze current state

• Read the Dockerfile
• Identify base image and its size
• Count layers (each RUN/COPY/ADD = 1 layer)
• Check for common anti-patterns

2. Apply optimization checklist

   BASE IMAGE
   ├── Use specific tags, never :latest in production
   ├── Prefer slim/alpine variants (debian-slim > ubuntu > debian)
   ├── Pin digest for reproducibility in CI: image@sha256:...
   └── Match base to runtime needs (don't use python:3.12 for a compiled binary)

   LAYER OPTIMIZATION
   ├── Combine related RUN commands with && \
   ├── Order layers: least-changing first (deps before source code)
   ├── Clean package manager cache in the same RUN layer
   ├── Use .dockerignore to exclude unnecessary files
   └── Separate build deps from runtime deps

   BUILD CACHE
   ├── COPY dependency files before source code (package.json, requirements.txt, go.mod)
   ├── Install deps in a separate layer from code copy
   ├── Use BuildKit cache mounts: --mount=type=cache,target=/root/.cache
   └── Avoid COPY . . before dependency installation

   MULTI-STAGE BUILDS
   ├── Stage 1: build (full SDK, build tools, dev deps)
   ├── Stage 2: runtime (minimal base, only production artifacts)
   ├── COPY --from=builder only what's needed
   └── Final image should have NO build tools, NO source code, NO dev deps
   

3. Generate optimized Dockerfile

• Apply all relevant optimizations
• Add inline comments explaining each decision
• Report estimated size reduction

4. Validate

   python3 scripts/dockerfile_analyzer.py Dockerfile
   

/docker:compose — Docker Compose Configuration

1. Identify services

• Application (web, API, worker)
• Database (postgres, mysql, redis, mongo)
• Cache (redis, memcached)
• Queue (rabbitmq, kafka)
• Reverse proxy (nginx, traefik, caddy)

2. Apply compose best practices

   SERVICES
   ├── Use depends_on with condition: service_healthy
   ├── Add healthchecks for every service
   ├── Set resource limits (mem_limit, cpus)
   ├── Use named volumes for persistent data
   └── Pin image versions

   NETWORKING
   ├── Create explicit networks (don't rely on default)
   ├── Separate frontend and backend networks
   ├── Only expose ports that need external access
   └── Use internal: true for backend-only networks

   ENVIRONMENT
   ├── Use env_file for secrets, not inline environment
   ├── Never commit .env files (add to .gitignore)
   ├── Use variable substitution: ${VAR:-default}
   └── Document all required env vars

   DEVELOPMENT vs PRODUCTION
   ├── Use compose profiles or override files
   ├── Dev: bind mounts for hot reload, debug ports exposed
   ├── Prod: named volumes, no debug ports, restart: unless-stopped
   └── docker-compose.override.yml for dev-only config
   

3. Generate compose file

• Output docker-compose.yml with healthchecks, networks, volumes
• Generate .env.example with all required variables documented
• Add dev/prod profile annotations

/docker:security — Container Security Audit

1. Dockerfile audit

| Check | Severity | Fix |

|-------|----------|-----|

| Running as root | Critical | Add USER nonroot after creating user |

| Using :latest tag | High | Pin to specific version |

| Secrets in ENV/ARG | Critical | Use BuildKit secrets: --mount=type=secret |

| COPY with broad glob | Medium | Use specific paths, add .dockerignore |

| Unnecessary EXPOSE | Low | Only expose ports the app uses |

| No HEALTHCHECK | Medium | Add HEALTHCHECK with appropriate interval |

| Privileged instructions | High | Avoid --privileged, drop capabilities |

| Package manager cache retained | Low | Clean in same RUN layer |

2. Runtime security checks

| Check | Severity | Fix |

|-------|----------|-----|

| Container running as root | Critical | Set user in Dockerfile or compose |

| Writable root filesystem | Medium | Use read_only: true in compose |

| All capabilities retained | High | Drop all, add only needed: cap_drop: [ALL] |

| No resource limits | Medium | Set mem_limit and cpus |

| Host network mode | High | Use bridge or custom network |

| Sensitive mounts | Critical | Never mount /etc, /var/run/docker.sock in prod |

| No log driver configured | Low | Set logging: with size limits |

3. Generate security report

   SECURITY AUDIT — [Dockerfile/Image name]
   Date: [timestamp]

   CRITICAL: [count]
   HIGH:     [count]
   MEDIUM:   [count]
   LOW:      [count]

   [Detailed findings with fix recommendations]
   

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Tooling

scripts/dockerfile_analyzer.py

CLI utility for static analysis of Dockerfiles.

Features:

• Layer count and optimization suggestions
• Base image analysis with size estimates
• Anti-pattern detection (15+ rules)
• Security issue flagging
• Multi-stage build detection and validation
• JSON and text output

Usage:

# Analyze a Dockerfile
python3 scripts/dockerfile_analyzer.py Dockerfile

# JSON output
python3 scripts/dockerfile_analyzer.py Dockerfile --output json

# Analyze with security focus
python3 scripts/dockerfile_analyzer.py Dockerfile --security

# Check a specific directory
python3 scripts/dockerfile_analyzer.py path/to/Dockerfile

scripts/compose_validator.py

CLI utility for validating docker-compose files.

Features:

• Service dependency validation
• Healthcheck presence detection
• Network configuration analysis
• Volume mount validation
• Environment variable audit
• Port conflict detection
• Best practice scoring

Usage:

# Validate a compose file
python3 scripts/compose_validator.py docker-compose.yml

# JSON output
python3 scripts/compose_validator.py docker-compose.yml --output json

# Strict mode (fail on warnings)
python3 scripts/compose_validator.py docker-compose.yml --strict

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Multi-Stage Build Patterns

Pattern 1: Compiled Language (Go, Rust, C++)

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

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

Pattern 2: Node.js / TypeScript

# Dependencies stage
FROM node:20-alpine AS deps
WORKDIR /app
COPY package.json package-lock.json ./
RUN npm ci --production=false

# Build stage
FROM deps AS builder
COPY . .
RUN npm run build

# Runtime stage
FROM node:20-alpine
WORKDIR /app
RUN addgroup -g 1001 -S appgroup && adduser -S appuser -u 1001
COPY --from=builder /app/dist ./dist
COPY --from=deps /app/node_modules ./node_modules
COPY package.json ./
USER appuser
EXPOSE 3000
CMD ["node", "dist/index.js"]

Pattern 3: Python

# Build stage
FROM python:3.12-slim AS builder
WORKDIR /app
COPY requirements.txt .
RUN pip install --no-cache-dir --prefix=/install -r requirements.txt

# Runtime stage
FROM python:3.12-slim
WORKDIR /app
RUN groupadd -r appgroup && useradd -r -g appgroup appuser
COPY --from=builder /install /usr/local
COPY . .
USER appuser
EXPOSE 8000
CMD ["python", "-m", "uvicorn", "main:app", "--host", "0.0.0.0", "--port", "8000"]

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Base Image Decision Tree

Is it a compiled binary (Go, Rust, C)?
├── Yes → distroless/static or scratch
└── No
    ├── Need a shell for debugging?
    │   ├── Yes → alpine variant (e.g., node:20-alpine)
    │   └── No → distroless variant
    ├── Need glibc (not musl)?
    │   ├── Yes → slim variant (e.g., python:3.12-slim)
    │   └── 

… (full content is in the download package)