Docker

{
  "name": "docker",
  "version": "1.0.0",
  "category": "universal",
  "toolchain": "universal",
  "tags": [
    "docker",
    "containers",
    "devops",
    "infrastructure",
    "deployment"
  ],
  "entry_point_tokens": 78,
  "full_tokens": 7794,
  "related_skills": [],
  "author": "claude-mpm-skills",
  "license": "MIT",
  "created": "2025-11-30",
  "updated": "2025-12-31",
  "source_path": "toolchains/universal/infrastructure/docker/SKILL.md",
  "repository": "https://github.com/bobmatnyc/claude-mpm-skills",
  "subcategory": "infrastructure"
}


---
name: docker
description: Docker containerization for packaging applications with dependencies into isolated, portable units ensuring consistency across development, testing, and production environments.
user-invocable: false
disable-model-invocation: true
progressive_disclosure:
  entry_point:
    - summary
    - when_to_use
    - quick_start
  sections:
    - core_concepts
    - dockerfile_basics
    - multi_stage_builds
    - docker_compose
    - development_workflows
    - production_patterns
    - framework_examples
    - orchestration
    - debugging
    - troubleshooting
    - best_practices
---

# Docker Containerization Skill

## Summary
Docker provides containerization for packaging applications with their dependencies into isolated, portable units. Containers ensure consistency across development, testing, and production environments, eliminating "works on my machine" problems.

## When to Use
- **Local Development**: Consistent dev environments across team members
- **CI/CD Pipelines**: Reproducible build and test environments
- **Microservices**: Isolated services with independent scaling
- **Production Deployment**: Portable applications across cloud providers
- **Database/Service Testing**: Ephemeral databases for integration tests
- **Legacy Application Isolation**: Run incompatible dependencies side-by-side

## Quick Start

### 1. Create Dockerfile
```dockerfile
FROM node:18-alpine
WORKDIR /app
COPY package*.json ./
RUN npm ci --only=production
COPY . .
EXPOSE 3000
CMD ["node", "server.js"]
```

### 2. Build Image
```bash
docker build -t myapp:1.0 .
```

### 3. Run Container
```bash
docker run -p 3000:3000 myapp:1.0
```

---

## Core Concepts

### Images vs Containers
- **Image**: Read-only template with application code, runtime, and dependencies
- **Container**: Running instance of an image with writable layer
- **Registry**: Storage for images (Docker Hub, GitHub Container Registry)

### Layers and Caching
Each Dockerfile instruction creates a layer. Docker caches unchanged layers for faster builds.

```dockerfile
# GOOD: Dependencies change less frequently than code
FROM python:3.11-slim
COPY requirements.txt .
RUN pip install -r requirements.txt  # Cached unless requirements.txt changes
COPY . .                              # Rebuild only when code changes

# BAD: Invalidates cache on every code change
FROM python:3.11-slim
COPY . .                              # Changes frequently
RUN pip install -r requirements.txt  # Reinstalls on every build
```

### Volumes
Persistent data storage that survives container restarts.

```bash
# Named volume (managed by Docker)
docker run -v mydata:/app/data myapp

# Bind mount (host directory)
docker run -v $(pwd)/data:/app/data myapp

# Anonymous volume (temporary)
docker run -v /app/data myapp
```

### Networks
Containers communicate through Docker networks.

```bash
# Create network
docker network create mynetwork

# Run containers on network
docker run --network mynetwork --name db postgres
docker run --network mynetwork --name app myapp
# App can connect to db using hostname "db"
```

---

## Dockerfile Basics

### Essential Instructions

```dockerfile
# Base image
FROM node:18-alpine

# Metadata
LABEL maintainer="dev@example.com"
LABEL version="1.0"

# Set working directory
WORKDIR /app

# Copy files
COPY package*.json ./
COPY src/ ./src/

# Run commands (creates layer)
RUN npm ci --only=production

# Set enviro