Introduction to Docker - Docker & DevOps Tutorial | TechLead

What is Docker?

Docker is an open-source platform that automates the deployment, scaling, and management of applications using containerization. Containers package an application and all its dependencies into a standardized unit, ensuring it runs the same way on any machine — from your laptop to production servers.

Why Docker?

Consistency: "Works on my machine" is no longer a problem — containers run identically everywhere
Isolation: Each container runs in its own environment, preventing dependency conflicts
Portability: Move containers between development, staging, and production effortlessly
Efficiency: Containers share the host OS kernel and use far fewer resources than virtual machines
Speed: Containers start in seconds, making development and deployment much faster

Containers vs Virtual Machines

While virtual machines (VMs) include a full guest operating system, containers share the host OS kernel and only package the application and its dependencies. This makes containers significantly lighter and faster.

Comparison

Feature	Container	Virtual Machine
Startup Time	Seconds	Minutes
Size	MBs	GBs
OS	Shares host kernel	Full guest OS
Isolation	Process-level	Full isolation
Performance	Near-native	Overhead from hypervisor

Docker Architecture

Docker uses a client-server architecture with these key components:

Docker Daemon (dockerd): Runs on the host and manages containers, images, networks, and volumes
Docker Client (docker): The CLI tool you use to interact with the daemon
Docker Registry: A repository for Docker images (e.g., Docker Hub)
Docker Images: Read-only templates used to create containers
Docker Containers: Running instances of images

Installing Docker

macOS

# Install Docker Desktop for macOS
# Download from https://www.docker.com/products/docker-desktop/
# Or use Homebrew:
brew install --cask docker

Linux (Ubuntu/Debian)

# Update packages
sudo apt-get update

# Install dependencies
sudo apt-get install ca-certificates curl gnupg

# Add Docker's official GPG key
sudo install -m 0755 -d /etc/apt/keyrings
curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo gpg --dearmor -o /etc/apt/keyrings/docker.gpg

# Set up the repository
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

# Install Docker Engine
sudo apt-get update
sudo apt-get install docker-ce docker-ce-cli containerd.io docker-buildx-plugin docker-compose-plugin

Windows

# Install Docker Desktop for Windows
# Download from https://www.docker.com/products/docker-desktop/
# Requires WSL 2 backend
wsl --install

Verify Installation

# Check Docker version
docker --version
# Docker version 27.x.x, build xxxxx

# Run a test container
docker run hello-world

# Check Docker info
docker info

Your First Container

# Pull and run an nginx web server
docker run -d -p 8080:80 --name my-web nginx

# Visit http://localhost:8080 in your browser!

# See running containers
docker ps

# Stop the container
docker stop my-web

# Remove the container
docker rm my-web

Key Takeaways

✅ Docker packages apps into portable, isolated containers
✅ Containers are lighter and faster than VMs
✅ Docker ensures consistency across all environments
✅ The Docker ecosystem includes images, containers, registries, and orchestration tools