Here’s a polished reference document based on your raw notes, organized and enriched with contextual details for better understanding and usability. This can serve as a training handout or quick reference for someone learning Docker fundamentals.

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🐳 Docker: A Practical Guide to App Runtime and Containerization

📌 Overview: It’s All About Running the App!

To deploy modern applications efficiently, we transition through multiple abstractions:

Physical Server → Virtual Server → Container

Type	Startup Time
Physical Server	5 minutes
Virtual Machine	20 seconds
Container	~1 second

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🐳 What is Docker?

Docker is a container management platform that enables the building, shipping, and running of applications consistently across different environments.

✅ Why Use Docker?

• Saves Time – Fast setup, teardown, and portability.
• Reduces Cost – Lower overhead compared to VMs.
• Improves Quality – Ensures consistency across development and production.

Container = Lightweight app runtime environment packaged with all its dependencies.

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🧪 Assignment #1: How Do Containers Work?

Container Architecture

Unlike VMs, containers share the host OS kernel. They are isolated, fast, and lightweight.

Virtual Machine Components

• Hypervisor: Manages VMs (e.g., VirtualBox, VMware).
• Image (ISO): Contains OS + Kernel + Apps.
• Boot Process: Hypervisor → Kernel (BOOTFS) → Root Filesystem (ROOTFS) → App

Docker Components

Component	Purpose
Docker Engine	The core engine to build/run containers
Docker Image	Template that includes ROOTFS + app (e.g., ubuntu + java)
Docker Registry	Public (e.g., Docker Hub) or private image storage
Docker Container	Running instance created from an image

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🧱 Ubuntu as a Docker Image

• Ubuntu Image = Linux Kernel (host) + ROOTFS of Ubuntu

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🛠 Docker Installation and Setup Steps

Step 1 – Install Docker

sudo apt-get update
sudo apt-get install ca-certificates curl gnupg lsb-release
sudo mkdir -p /etc/apt/keyrings
curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo gpg --dearmor -o /etc/apt/keyrings/docker.gpg
echo \
  "deb [arch=$(dpkg --print-architecture) signed-by=/etc/apt/keyrings/docker.gpg] \
  https://download.docker.com/linux/ubuntu $(lsb_release -cs) stable" | \
  sudo tee /etc/apt/sources.list.d/docker.list > /dev/null
sudo apt-get update
sudo apt-get install docker-ce docker-ce-cli containerd.io docker-compose-plugin
Code language: PHP (php)

Step 2 – Download Docker Image

docker pull httpd

Step 3 – Manage Docker Containers

docker create httpd
docker start <container_id>
docker stop <container_id>
docker restart <container_id>
docker pause <container_id>
docker unpause <container_id>
docker kill <container_id>
docker rm <container_id>
Code language: HTML, XML (xml)

Step 4 – Connect to Running Container

docker exec -it <container_id> /bin/bash
Code language: HTML, XML (xml)

Step 5 – Expose Container to Host

docker run -d -p 80:80 httpd
Code language: CSS (css)

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⚙️ Docker Run Modes

Command	Behavior
docker run	pull + create + start + attach to STDOUT
docker run -d	pull + create + start (run in detached mode)

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🧠 Behind the Scenes: Process Flow

HUMAN → docker CLI → dockerd → containerd → kernel

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🧪 Sample Docker Commands

Action	Command Example
Check Docker Info	docker info
Pull Image	docker pull httpd
List Images	docker images
Run Container	docker run -d httpd
Map Port	docker run -d -p 80:80 httpd
Inspect Container	docker inspect <container_id>
Access Container	docker exec -it <id> /bin/bash
Show Stats	docker stats

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📚 References and Further Learning

• 📖 Complete Docker CLI Reference
• 🛠 How to Install Docker in Linux
• 🤔 What is Docker?
• 🏗 Docker Architecture & Components Explained

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