Lesson 06 — Docker Basics

Lesson Overview

Imagine you’re developing a Python application.

It works perfectly on your laptop.

You send it to another developer.

Suddenly, it doesn’t work.

Why?

Because their computer has:

Different Python version
Different operating system
Missing libraries
Different configurations

This is known as the classic:

“It works on my machine.”

Docker solves this problem.

Docker packages an application together with everything it needs to run:

Application code
Libraries
Dependencies
Runtime
Configuration

This package is called a Container.

Containers ensure that applications run the same way everywhere.

Today, Docker is one of the most important technologies in Cloud Computing, DevOps, Platform Engineering, AI, and Cybersecurity.

Learning Objectives

After completing this lesson, you will be able to:

Understand containerization.
Learn Docker architecture.
Install Docker.
Work with Docker images.
Run Docker containers.
Create Dockerfiles.
Build Docker images.
Use Docker Hub.
Manage Docker volumes and networking.
Apply Docker in enterprise environments.

What is Docker?

Docker is an open-source platform used to build, package, ship, and run applications inside lightweight containers.

Instead of installing software directly on an operating system, applications run inside isolated containers.

Docker provides:

Consistency
Portability
Isolation
Scalability
Fast deployment

Why Docker Matters

Docker helps organizations:

Eliminate environment issues
Simplify deployments
Improve scalability
Speed up development
Standardize environments
Support microservices

Docker has become a standard technology in modern software development.

What is a Container?

A container is an isolated environment that contains everything an application needs to run.

A container includes:

Application
Runtime
Libraries
Dependencies
Configuration Files

Unlike virtual machines, containers share the host operating system kernel, making them lightweight and fast.

Containers vs Virtual Machines

Virtual Machine	Docker Container
Includes Guest OS	Shares Host OS
Larger Size	Lightweight
Slower Startup	Starts in Seconds
Higher Resource Usage	Lower Resource Usage
Full Virtualization	Operating System-Level Virtualization

Containers are more efficient for most modern applications.

Docker Architecture

Docker consists of several components.

Developer

↓

Docker CLI

↓

Docker Engine

↓

Docker Images

↓

Docker Containers

Each component plays a specific role in managing containers.

Docker Components

Docker includes:

Docker Client
Docker Engine
Docker Daemon
Docker Images
Docker Containers
Docker Registry

Together they provide a complete container platform.

Docker Images

A Docker Image is a read-only template used to create containers.

Think of an image as a blueprint.

Example:

Python Image

↓

Run Container

↓

Python Application

Images can be reused to create multiple containers.

Docker Containers

Containers are running instances of Docker images.

Example:

Docker Image

↓

Container 1

↓

Container 2

↓

Container 3

Each container runs independently.

Docker Hub

Docker Hub is the public repository for Docker images.

Popular images include:

Ubuntu
Alpine
Python
Nginx
MySQL
PostgreSQL
Redis
Jenkins

Developers download images instead of creating everything from scratch.

Installing Docker

Download Docker Desktop from:

https://www.docker.com/products/docker-desktop

Verify installation:

docker --version

Example:

Docker version 28.x.x

Running Your First Container

Run the Hello World container.

docker run hello-world

Docker automatically:

Downloads the image
Creates a container
Executes it
Displays the output

This confirms Docker is working correctly.

Pulling Images

Download an image.

docker pull ubuntu

Download Python:

docker pull python

Images are stored locally after downloading.

Viewing Images

Display downloaded images.

docker images

Example output:

python

ubuntu

nginx

Running Containers

Start an Ubuntu container.

docker run ubuntu

Interactive mode:

docker run -it ubuntu bash

The -it option provides an interactive terminal.

Listing Running Containers

View active containers.

docker ps

View all containers:

docker ps -a

These commands help monitor container status.

Stopping Containers

Stop a running container.

docker stop container_id

Replace container_id with the actual container identifier.

Removing Containers

Delete a container.

docker rm container_id

Removing unused containers keeps your environment clean.

Removing Images

Delete an image.

docker rmi image_name

Example:

docker rmi ubuntu

Dockerfile

A Dockerfile defines how to build a Docker image.

Example:

FROM python:3.12

WORKDIR /app

COPY . .

RUN pip install -r requirements.txt

CMD ["python","app.py"]

Docker reads the instructions from top to bottom.

Building an Image

Build an image from a Dockerfile.

docker build -t myapp .

The -t flag assigns a name (tag) to the image.

Running Your Image

docker run myapp

Docker creates a container from the image.

Docker Volumes

Containers are temporary.

Volumes provide persistent storage.

Example:

docker volume create app-data

Volumes allow data to survive container restarts and replacements.

Docker Networking

Containers communicate using Docker networks.

Create a network:

docker network create app-network

Networking enables communication between multiple containers.

Docker Compose (Introduction)

Docker Compose manages multi-container applications.

Example:

services:

  web:

    image: nginx

  database:

    image: mysql

Compose allows multiple services to start together using a single command.

Common Docker Commands

Command	Purpose
docker pull	Download image
docker images	List images
docker run	Create container
docker ps	List running containers
docker stop	Stop container
docker rm	Remove container
docker rmi	Remove image
docker build	Build image
docker logs	View logs
docker exec	Execute command inside container

Docker in Cloud Computing

Cloud Engineers use Docker for:

Microservices
Application Packaging
Serverless Development
Kubernetes Deployments
Cloud Migration

Containers simplify application portability across cloud providers.

Docker in DevOps

DevOps Engineers use Docker to:

Build CI/CD pipelines
Standardize development environments
Deploy applications
Create reproducible builds
Run automated tests

Docker is a core DevOps technology.

Docker in Cybersecurity

Security teams use Docker for:

Security testing labs
Malware analysis
Sandboxed environments
Vulnerability scanning
Container security assessments

Containers provide isolated environments for testing and analysis.

Docker in AI

AI Engineers use Docker to package:

Machine Learning Models
Jupyter Notebooks
TensorFlow Applications
PyTorch Projects
AI APIs

Containers ensure AI workloads run consistently across environments.

Common Beginner Mistakes

Avoid these mistakes:

Running containers as root unnecessarily.
Storing secrets inside Docker images.
Creating oversized images.
Ignoring image updates.
Leaving unused containers running.
Forgetting to persist important data with volumes.

Following best practices improves security and efficiency.

Enterprise Best Practices

Professional teams:

Use official base images.
Keep images lightweight.
Scan images for vulnerabilities.
Use version tags.
Store secrets securely.
Use multi-stage builds.
Remove unused images regularly.
Monitor container health.

These practices improve reliability and security.

Real-World Example

A DevOps Engineer deploys a web application.

Workflow:

Write Application

↓

Create Dockerfile

↓

Build Docker Image

↓

Push Image to Registry

↓

Deploy Container

↓

Application Running

The same Docker image can run on a developer’s laptop, a test environment, or a production Kubernetes cluster without modification.

Key Takeaways

After completing this lesson, you should understand:

Docker.
Containers.
Images.
Docker Hub.
Dockerfile.
Docker Build.
Docker Run.
Docker Volumes.
Docker Networking.
Docker Best Practices.

Summary

Docker revolutionized software development by making applications portable, consistent, and easy to deploy.

By packaging applications and their dependencies into lightweight containers, Docker enables developers and operations teams to build, test, ship, and run software reliably across different environments.

Docker is now a foundational technology for Cloud Computing, DevOps, Artificial Intelligence, Cybersecurity, and modern application development.

Next Lesson

➡️ Lesson 07 — Infrastructure as Code (IaC)

In the next lesson, you’ll learn how to automate infrastructure provisioning using Infrastructure as Code (IaC). You’ll explore Terraform, AWS CloudFormation, declarative infrastructure, version-controlled deployments, and enterprise infrastructure automation practices.