---
name: docker-6f6b63c6bb31
description: Build, run, and secure Docker containers with current best practices. Use for Dockerfile review, multi-stage builds, Compose orchestration, image hardening, and CI/CD integration.
metadata:
  category: user-invoked
disable-model-invocation: true
---

Default output: return only the result, blockers, and required evidence. Omit preambles, process narration, repeated context, confidence scores, and follow-up offers. Use at most five bullets unless a required artifact or schema needs more.

# Docker Container Engineering

## Current Versions (Verify Before Use)

```bash
docker --version          # Engine version
docker compose version    # Compose plugin version
docker buildx version     # BuildKit/buildx version
```

Check the [Docker Engine release notes](https://docs.docker.com/engine/release-notes/) for the latest stable.

## Core Principles

1. **Multi-stage builds are the default.** Every production Dockerfile should use multi-stage builds to minimize attack surface and image size.
2. **Non-root containers.** Every container should run as a non-root user unless impossible.
3. **Layer caching is a first-class concern.** Order Dockerfile instructions from least-frequently-changing to most-frequently-changing.
4. **Healthchecks are mandatory.** Every long-running container must define a `HEALTHCHECK`.
5. **Scan before push.** Every image should pass a security scan before registry upload.

## Dockerfile Review Checklist

### Structure
- [ ] Uses multi-stage build (at least 2 stages: builder + runtime)
- [ ] Base image is a slim or distroless variant (`alpine`, `slim`, `distroless`)
- [ ] No `latest` tag — pinned to specific digest or version
- [ ] `WORKDIR` is set before file operations
- [ ] `COPY` uses specific files, not `COPY . .` where possible

### Security
- [ ] Runs as non-root (`USER` directive or `--user` at runtime)
- [ ] No secrets in layers (use BuildKit secrets or runtime mounts)
- [ ] `EXPOSE` documents only necessary ports
- [ ] `HEALTHCHECK` is defined
- [ ] No unnecessary packages installed (`apt-get` cleaned, no dev tools in runtime)
- [ ] Image scanned with `docker scout` or Trivy

### Efficiency
- [ ] `.dockerignore` exists and excludes: `.git`, `node_modules`, `*.log`, `.env`
- [ ] Layer order respects cache invalidation (dependencies before code)
- [ ] `RUN` commands combined where logical (but not excessively long)
- [ ] BuildKit enabled (`DOCKER_BUILDKIT=1` or default in modern Docker)

## Multi-Stage Build Template

```dockerfile
# syntax=docker/dockerfile:1
FROM node:22-alpine AS builder
WORKDIR /app
COPY package*.json .
RUN npm ci --only=production

FROM node:22-alpine AS runtime
RUN addgroup -g 1001 -S nodejs && adduser -S nodejs -u 1001
WORKDIR /app
COPY --from=builder --chown=nodejs:nodejs /app/node_modules ./node_modules
COPY --chown=nodejs:nodejs . .
USER nodejs
EXPOSE 3000
HEALTHCHECK --interval=30s --timeout=3s --start-period=5s --retries=3 \
  CMD node -e "require('http').get('http://localhost:3000/health', (r) => r.statusCode === 200 ? process.exit(0) : process.exit(1))"
CMD ["node", "server.js"]
```

## Docker Compose Patterns

### Development vs Production Separation
```yaml
# docker-compose.yml — production baseline
services:
  app:
    build: .
    restart: unless-stopped
    deploy:
      resources:
        limits:
          cpus: '1.0'
          memory: 512M
    healthcheck:
      test: ["CMD", "curl", "-f", "http://localhost:3000/health"]
      interval: 30s
      timeout: 3s
      retries: 3
```

```yaml
# docker-compose.override.yml — development only
services:
  app:
    volumes:
      - .:/app
    environment:
      - NODE_ENV=development
    command: npm run dev
```

### Validation
```bash
docker compose config              # validate and merge
docker compose config --profiles   # check profile separation
```

## Security Scanning

```bash
# Docker Scout (built-in, requires login)
docker scout quickview myimage:latest
docker scout cves myimage:latest

# Trivy (open source)
trivy image myimage:latest
trivy filesystem .

# Snyk
snyk container test myimage:latest
```

## Common Anti-Patterns

| Anti-Pattern | Why It's Wrong | Fix |
|---|---|---|
| `FROM node:latest` | Non-reproducible builds, surprise updates | Pin to `node:22-alpine` or digest |
| Running as root | Container escape = host compromise | `USER` directive + file ownership |
| `COPY . .` without `.dockerignore` | Bloats image, leaks secrets | Explicit `.dockerignore` |
| `apt-get update && apt-get install` without cleanup | Bloated layers | `&& rm -rf /var/lib/apt/lists/*` |
| No healthcheck | Orchestrator can't detect failure | `HEALTHCHECK` in Dockerfile or compose |
| Secrets in ENV | Visible in `docker inspect` | BuildKit secrets or runtime mounts |
| Single-stage build | Large attack surface, slow deploys | Multi-stage: build → runtime |

## CI/CD Integration

```yaml
# .github/workflows/docker.yml
- name: Build and scan
  run: |
    docker build -t app:${{ github.sha }} .
    docker scout cves app:${{ github.sha }} --exit-code --only-severity critical,high
    docker run --rm app:${{ github.sha }} npm test
```

## Troubleshooting Flow

1. **Build fails:** Check layer cache — `docker build --no-cache` to isolate
2. **Image too large:** Run `dive myimage:latest` to analyze layer bloat
3. **Container exits immediately:** Check `CMD`/`ENTRYPOINT` and logs (`docker logs`)
4. **Permission denied:** Verify `USER` directive and file ownership in `COPY --chown`
5. **Healthcheck failing:** Test command inside container with `docker exec`

## Official Resources

- [Dockerfile reference](https://docs.docker.com/engine/reference/builder/)
- [Compose specification](https://docs.docker.com/compose/compose-file/)
- [Docker security best practices](https://docs.docker.com/develop/dev-best-practices/)
- [BuildKit documentation](https://docs.docker.com/build/buildkit/)
- [Docker Scout](https://docs.docker.com/scout/)


---
Source attribution: v1truv1us
Original project: https://github.com/v1truv1us/ai-eng-system/blob/eaff192b6e8bcb204a1f1b132b98f748a9b4572e/plugins/ai-eng-devops/skills/docker/SKILL.md
License: MIT
License information: https://opensource.org/license/mit
Original upstream instructions; downloaded from Mega AI Hub.

## Upstream license notice

MIT License

Copyright (c) 2025 John Ferguson

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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SOFTWARE.



# Mega AI Hub resource metadata

Creator / publisher: v1truv1us
Original project: https://github.com/v1truv1us/ai-eng-system/blob/eaff192b6e8bcb204a1f1b132b98f748a9b4572e/plugins/ai-eng-devops/skills/docker/SKILL.md
Attribution basis: Source repository record

Fields of work: Development & Engineering
Roles: Backend Developer, DevOps / SRE, Full-Stack Developer
Specialties: Backend, DevOps
Tools: Docker
Country applicability: Country not specified
Classification basis: Source catalog labels
Instruction SHA-256: d3ba73690467a49c5a930d0bde11ce7d8a339e355b024a2805d99e266b3bdd5d