🐳 Docker Tutorial – Complete Beginner to Advanced Guide

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🧠 Introduction to Docker

📌 What is Docker?

Docker is an open-source containerization platform that simplifies building, shipping, and running applications across environments. It packages applications and their dependencies into containers, making them portable and consistent.

🎯 Why Use Docker?

“It works on my machine” is no longer an excuse.

Docker ensures consistent environments across development, testing, and production. It reduces bugs caused by environmental differences.

🧱 Key Concepts in Docker

• Image – Blueprint for containers
• Container – Running instance of an image
• Dockerfile – Script to automate image creation
• Docker Hub – Cloud registry for sharing images

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🔧 Getting Started with Docker

🧰 Prerequisites

• Basic command-line knowledge
• Familiarity with Linux
• Admin rights on your system

💻 Installing Docker

🖥 Docker Desktop (Windows/macOS)

• Download from docker.com
• Run the installer and complete setup
• Verify with: docker --version

🐧 Docker Engine (Linux)

sudo apt update
sudo apt install docker-ce docker-ce-cli containerd.io

🧬 Docker Architecture

• Docker Daemon: Runs as a background service
• Docker Client: CLI tool to interact with Docker
• Registries: Repositories like Docker Hub that store images

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📦 Core Docker Components

🧱 Docker Images

📸 What is an Image?

An image is a read-only template that defines the environment your app will run in.

🛠 Building Docker Images

FROM node:18
WORKDIR /app
COPY . .
RUN npm install
CMD ["node", "app.js"]

Build the image:

docker build -t my-node-app .

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📦 Docker Containers

▶️ Creating and Running Containers

docker run -d -p 3000:3000 my-node-app

🛑 Stopping and Removing Containers

docker ps
docker stop <container_id>
docker rm <container_id>

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🧾 Dockerfile Basics

✍️ Writing a Dockerfile

• FROM – Base image
• COPY – Copy project files
• RUN – Execute shell commands
• CMD – Set container start command

✅ Best Practices

• Use .dockerignore
• Minimize image layers
• Pin exact versions

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🧠 Docker Commands Cheat Sheet

🖼 Image Commands

docker images
docker rmi <image_id>

📦 Container Commands

docker ps
docker logs <id>
docker exec -it <id> bash

🌐 Network & Volume Commands

docker network ls
docker volume ls

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🧰 Docker Compose

📌 What is Docker Compose?

A tool to define and manage multi-container Docker applications using a docker-compose.yml file.

⚙️ Installing Docker Compose

Docker Desktop includes Compose. On Linux:

sudo apt install docker-compose

🧾 Sample docker-compose.yml

version: "3"
services:
  web:
    build: .
    ports:
      - "5000:5000"
  redis:
    image: redis:alpine

▶️ Run with Compose

docker-compose up

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🌐 Working with Docker Hub

⬇️ Pull Images

docker pull nginx

⬆️ Push Images

docker tag my-app username/my-app
docker push username/my-app

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🛠 Real-World Use Cases

👨‍💻 Docker in Development

Quick setup of dev environments. No more dependency hell.

🧪 Docker in CI/CD Pipelines

Jenkins, GitHub Actions, and GitLab CI use Docker to ensure reliable builds/tests.

🚀 Production Deployment

Use orchestration tools like Kubernetes or Docker Swarm for high availability and scaling.

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🔥 Best Practices for Docker

• 🧊 Use smaller base images (e.g., Alpine)
• 📁 .dockerignore to exclude unnecessary files
• 🏷️ Tag images properly (e.g., myapp:1.0)

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🐞 Common Docker Issues and Fixes

🚫 Container Not Starting

docker logs <container_id>

⚠️ Port Conflicts

Ensure no other app is using the specified port.

🔐 Permission Issues

Use sudo or add your user to the Docker group:

sudo usermod -aG docker $USER

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🔐 Security in Docker

🛡 Docker Security Basics

• Avoid running as root inside containers
• Update base images frequently

👤 Run with Least Privileges

docker run --user 1000:1000 ...

Avoid --privileged unless absolutely necessary.

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🌍 Docker Ecosystem and Alternatives

🧑‍🚀 Podman vs Docker

Podman is rootless and daemonless — a good alternative in secure environments.

🧭 Kubernetes & Docker

Kubernetes can orchestrate Docker containers. However, recent versions support runtimes like containerd and CRI-O.

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🎯 Conclusion

Docker revolutionizes how we develop, test, and deploy software. It’s portable, fast, and scalable—ideal for both personal and enterprise projects. Master Docker to future-proof your development workflow.

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