🐳 Docker Cheatsheet – Quick Revision

🔹 Basics

• What is Docker?
  Platform to build, ship, and run applications in containers (lightweight, isolated environments).

• Key Components:

  • Image → Blueprint (read-only).

  • Container → Running instance of an image.

  • Dockerfile → Instructions to build an image.

  • Registry → Store/distribute images (e.g., Docker Hub).

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🔹 Common Commands

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🔹 Dockerfile Essentials

FROM ubuntu:20.04        # Base image
WORKDIR /app             # Set working dir
COPY . /app              # Copy files
RUN apt-get update && apt-get install -y python3
CMD ["python3", "app.py"] # Default command

👉 Build: docker build -t myapp .
👉 Run: docker run -d myapp

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🔹 Networking & Volumes

• Ports: docker run -p 8080:80 nginx → Host:8080 → Container:80

• Volumes (persistent data):

  • docker run -v /host/data:/container/data mysql

• Read-only volume:

  • docker run -v /host/data:/container/data:ro nginx

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🔹 Docker Compose

• Define multi-container apps (docker-compose.yml):

version: '3'
services:
  web:
    image: nginx
    ports:
      - "8080:80"
  db:
    image: mysql
    environment:
      MYSQL_ROOT_PASSWORD: root

👉 Run: docker-compose up -d

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🔹 Best Practices

• Use .dockerignore to avoid copying unnecessary files.

• Use multi-stage builds for smaller images.

• Keep containers stateless → use volumes for data.

• Tag images (myapp:v1) instead of using latest.

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⚡️ Quick Tip: Containers are ephemeral. Always use volumes for persistence.