Docker: An Introduction

1. The Big Idea: What Problem Does Docker Solve?
2. Core Concepts: The Building Blocks
3. The Docker Workflow: A Practical Cycle
4. Essential Docker Commands (Hands-On)
5. Your First Dockerfile: A Simple Example
6. Key Benefits & Advantages
7. Docker vs. Virtual Machines (VMs)
8. Next Steps & Advanced Topics
Summary

1. The Big Idea: What Problem Does Docker Solve?

Imagine this classic scenario:

"It works on my machine!" - A developer says code runs perfectly on their laptop.
"But it's broken on the server!" - The operations team can't get it to run in production.

The problem is environment inconsistency. Different machines have different operating systems, software versions, libraries, and configurations.

Docker solves this by using containerization.

Analogy: Shipping Containers

Instead of shipping goods loose on a ship (error-prone), we pack everything into a standard-sized container.
Similarly, a Docker container packages your application code, along with all its dependencies, into a standardized unit.
This container can run reliably anywhere Docker is installed.

2. Core Concepts: The Building Blocks

a) Docker Image

A read-only template. Think of it as a blueprint for creating containers. Images are immutable.

b) Docker Container

A running instance of an image. You can run multiple containers from the same image. They are isolated.

c) Dockerfile

A text file with instructions for building images. Defines base image, dependencies, copied files, and startup command.

d) Docker Engine

Core software including the Docker Daemon, REST API, and CLI.

e) Docker Hub / Registry

A repository for images. Like GitHub but for Docker images.

3. The Docker Workflow: A Practical Cycle

Create a Dockerfile
Build an Image using docker build
Run a Container using docker run
Test and iterate
Share image via registry

4. Essential Docker Commands (Hands-On)

Examples:

docker run hello-world

docker run -p 8080:80 nginx

5. Your First Dockerfile: A Simple Example

Containerizing a Python Flask app:

app.py

from flask import Flask
app = Flask(__name__)

@app.route('/')
def hello_world():
return 'Hello, Docker World!'

if __name__ == '__main__':
    app.run(debug = True, host = '0.0.0.0')

Dockerfile

FROM python: 3.9 - slim
WORKDIR / app
COPY requirements.txt.
RUN pip install - r requirements.txt
COPY. .
    EXPOSE 5000
CMD["python", "app.py"]

requirements.txt

Flask==2.1.0

6. Key Benefits & Advantages

Consistency
Isolation
Portability
Efficiency
Scalability
Microservices-ready

7. Docker vs. Virtual Machines (VMs)

Feature	VM	Docker Container
Guest OS	Full OS	Shares Host Kernel
Size	GBs	MBs
Boot Time	Minutes	Seconds

8. Next Steps & Advanced Topics

Docker Compose
Kubernetes
Best practices (dockerignore, alpine images, non-root users)

Summary

Docker solves "it works on my machine" by packaging apps and dependencies into containers. You learned about images, containers, Dockerfiles, workflows, commands, and best practices.

Isaac.