# Docker Quick Reference

*Containers, images, volumes, networking, compose*

> Source: Docker Documentation (docs.docker.com) · MIT

## Basics

### Running Containers

```
docker run nginx              # run image
docker run -d nginx           # detached (background)
docker run -p 8080:80 nginx   # map port
docker run --name web nginx   # named container
docker run -it ubuntu bash    # interactive shell
```

### Essential Commands

| Command | Description |
|---------|-------------|
| `docker ps` | List running containers |
| `docker ps -a` | List all containers (including stopped) |
| `docker images` | List local images |
| `docker pull nginx` | Download image from registry |
| `docker info` | System-wide information |

## Container Management

### Lifecycle

| Command | Description |
|---------|-------------|
| `docker start <id>` | Start a stopped container |
| `docker stop <id>` | Graceful stop (SIGTERM) |
| `docker kill <id>` | Force stop (SIGKILL) |
| `docker restart <id>` | Restart container |
| `docker rm <id>` | Remove stopped container |
| `docker rm -f <id>` | Force remove (even if running) |

### Inspection & Debugging

| Command | Description |
|---------|-------------|
| `docker logs <id>` | View container logs |
| `docker logs -f <id>` | Follow logs (live) |
| `docker exec -it <id> bash` | Shell into running container |
| `docker inspect <id>` | Detailed container metadata (JSON) |
| `docker top <id>` | Running processes in container |
| `docker stats` | Live resource usage |

### Copying Files

```
docker cp file.txt <id>:/app/    # host → container
docker cp <id>:/app/log.txt ./   # container → host
```

## Images

### Building & Tagging

```
docker build -t myapp .          # build from Dockerfile
docker build -t myapp:v2 .       # with tag
docker tag myapp user/myapp:v2   # retag image
```

### Publishing

```
docker login
docker push user/myapp:v2
docker pull user/myapp:v2
```

### Image Management

| Command | Description |
|---------|-------------|
| `docker images` | List all local images |
| `docker rmi <image>` | Remove image |
| `docker image prune` | Remove dangling images |
| `docker system prune` | Remove all unused data |
| `docker history <image>` | Show image layer history |

## Dockerfile

### Common Instructions

| Command | Description |
|---------|-------------|
| `FROM node:20` | Base image |
| `WORKDIR /app` | Set working directory |
| `COPY . .` | Copy files into image |
| `RUN npm install` | Run command during build |
| `CMD ["node", "app.js"]` | Default command at runtime |
| `EXPOSE 3000` | Document listening port |
| `ENV NODE_ENV=production` | Set environment variable |
| `ARG VERSION=latest` | Build-time variable |
| `ENTRYPOINT ["python"]` | Fixed executable (CMD = args) |

### Example Dockerfile

```
FROM node:20-alpine
WORKDIR /app
COPY package*.json ./
RUN npm ci --production
COPY . .
EXPOSE 3000
CMD ["node", "server.js"]
```

## Volumes

### Persistent Storage

```
docker volume create mydata
docker run -v mydata:/app/data nginx
docker run -v $(pwd):/app nginx  # bind mount
```

### Volume Commands

| Command | Description |
|---------|-------------|
| `docker volume ls` | List volumes |
| `docker volume inspect <v>` | Volume details |
| `docker volume rm <v>` | Remove volume |
| `docker volume prune` | Remove unused volumes |

## Networks

### Network Basics

```
docker network create mynet
docker run --network mynet --name api nginx
docker run --network mynet --name db postgres
```

### Network Commands

| Command | Description |
|---------|-------------|
| `docker network ls` | List networks |
| `docker network inspect <n>` | Network details |
| `docker network connect <n> <c>` | Attach container to network |
| `docker network rm <n>` | Remove network |

*Containers on the same network can reach each other by name*

## Docker Compose

### Example compose.yaml

```
services:
  web:
    build: .
    ports: ["3000:3000"]
    depends_on: [db]
  db:
    image: postgres:16
    environment:
      POSTGRES_PASSWORD: secret
    volumes: [pgdata:/var/lib/postgresql/data]
volumes:
  pgdata:
```

### Compose Commands

| Command | Description |
|---------|-------------|
| `docker compose up` | Start all services |
| `docker compose up -d` | Start in background |
| `docker compose down` | Stop and remove containers |
| `docker compose down -v` | Also remove volumes |
| `docker compose build` | Rebuild images |
| `docker compose logs -f` | Follow all service logs |
| `docker compose ps` | List running services |
| `docker compose exec web bash` | Shell into a service |

## Useful Patterns

### Cleanup Commands

```
docker system prune -a          # remove all unused
docker container prune           # remove stopped
docker image prune -a            # remove unused images
```

### Quick Recipes

| Command | Description |
|---------|-------------|
| `Temp container` | `docker run --rm -it alpine sh` |
| `Port check` | `docker port <id>` |
| `Env vars` | `docker run -e KEY=val image` |
| `Env file` | `docker run --env-file .env image` |
| `Restart policy` | `docker run --restart unless-stopped image` |
| `Resource limit` | `docker run --memory 512m --cpus 1 image` |