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DOCKER CHEATSHEET
Enterprise-ready Docker commands, patterns, and best practices for development and production environments

Category: DevOps · Type: cheatsheet
Official docs: https://docs.docker.com/

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## What is Docker?

**Docker** is an open-source containerization platform that packages applications and their dependencies into lightweight, portable containers. It ensures consistent behavior across development, testing, and production environments.

**⚡ Key Features**
- Lightweight container runtime
- Immutable application images
- Environment consistency
- Fast startup and scalability

**🎯 Use Cases**
- Microservices architecture
- CI/CD pipelines
- Cloud-native deployments
- Local dev parity with production

## 🛠️ Interactive Command Builder

Build a `docker run` command without memorizing flag order — fill in the fields below and copy the result.

## 📦 Docker - Install & Runtime Info

Verify Docker installation and daemon status.

```bash
docker --version
docker info
```

## 🐳 Docker - Run Containers

Run container in detached mode with port mapping.

```bash
docker run -d -p 8080:8080 --name my-app my-app:1.0
```

Run with environment variables.

```bash
docker run -d \
  -e SPRING_PROFILES_ACTIVE=prod \
  -p 8080:8080 \
  my-app:1.0
```

## 🔍 Docker - List, Inspect & Logs

List containers.

```bash
docker ps
docker ps -a
```

Inspect container.

```bash
docker inspect my-app
```

View logs.

```bash
docker logs my-app
docker logs -f my-app
```

## ⏸️ Docker - Start, Stop & Restart

```bash
docker stop my-app
docker start my-app
docker restart my-app
```

Graceful stop.

```bash
docker stop -t 30 my-app
```

## 📦 Docker - Image Lifecycle

Build and list images.

```bash
docker build -t my-app:1.0 .
docker images
```

Remove images.

```bash
docker rmi my-app:1.0
docker image prune -a
```

## 📂 Docker - Volumes & Persistence

Create and attach volumes.

```bash
docker volume create app-data
docker run -d -v app-data:/var/lib/app my-app:1.0
```

## 🌐 Docker - Networking Basics

```bash
docker network ls
docker network create app-network
```

Attach network.

```bash
docker run -d --network app-network my-app:1.0
```

## 🧱 Dockerfile - Best Practices

Minimal production Dockerfile.

```dockerfile
FROM eclipse-temurin:17-jre-alpine
WORKDIR /app
COPY target/app.jar app.jar
EXPOSE 8080
ENTRYPOINT ["java","-jar","app.jar"]
```

## ⚡ Dockerfile - Multi Stage Build

```dockerfile
FROM maven:3.9-eclipse-temurin-17 AS build
WORKDIR /build
COPY . .
RUN mvn clean package -DskipTests

FROM eclipse-temurin:17-jre-alpine
WORKDIR /app
COPY --from=build /build/target/app.jar app.jar
ENTRYPOINT ["java","-jar","app.jar"]
```

## 🔒 Docker - Run as Non Root

```dockerfile
RUN addgroup -S app && adduser -S app -G app
USER app
```

## 🛡️ Docker - Read Only Containers

```bash
docker run -d \
  --read-only \
  --tmpfs /tmp \
  my-app:1.0
```

## 🔐 Docker - Secrets Handling

```bash
docker run -d \
  -e DB_PASSWORD_FILE=/run/secrets/db_password \
  my-app:1.0
```

## 🔍 Docker - Image Vulnerability Scan

```bash
docker scan my-app:1.0
trivy image my-app:1.0
```

## 📊 Docker - Resource Monitoring

```bash
docker stats
```

## ⏱️ Docker - CPU & Memory Limits

```bash
docker run -d \
  --memory=512m \
  --cpus=1.5 \
  my-app:1.0
```

## 🚨 Docker - Restart Policies

```bash
docker run -d \
  --restart unless-stopped \
  my-app:1.0
```

## 🚀 Docker - CI Build Pattern

```bash
docker build -t my-app:${GIT_COMMIT} .
docker tag my-app:${GIT_COMMIT} my-app:latest
```

## 🔁 Docker - Tagging Strategy

```
my-app:1.2.4
my-app:1.2
my-app:latest
my-app:git-<sha>
```

## 🧪 Docker - Test Inside Container

```bash
docker run --rm my-app:test mvn test
```

## 🧰 Docker Compose - Basics

```bash
docker compose up -d
docker compose down
```

```yaml
services:
  app:
    image: my-app
    ports:
      - "8080:8080"
```

## 🧰 Docker Compose - Profiles

```yaml
services:
  app:
    profiles: ["prod"]
  mock:
    profiles: ["dev"]
```

```bash
docker compose --profile dev up
```

## 🚫 Troubleshoot - Restart Loop

```bash
docker logs my-app
docker inspect my-app --format='{{.State.ExitCode}}'
```

## 🚫 Troubleshoot - Disk Full

```bash
docker system df
docker system prune -a
```

## 💡 Enterprise Docker Golden Rules

- One container = one responsibility
- Never store secrets in images
- Always define resource limits
- Logs go to stdout/stderr
- Immutable builds only
- Scan images in CI
- Delete before debugging

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