🚢 The Container Challenge

Imagine you're shipping an app to production. Your code runs perfectly on your laptop, but it crashes on the server. Sound familiar?

Quick Experiment: Click the Containers

Click each container below to see what happens when dependencies aren't isolated:

📦

App A

Python 3.8

📦

App B

Python 3.11

🖥️

Shared Server

??? Python

📚 What's in this lesson

Docker fundamentals & commands
Docker Compose architecture
Key differences & use cases
Real-world decision framework
Hands-on examples

💡 Why this matters (WIIFM)

Eliminate "works on my machine"
Deploy faster with confidence
Manage complex multi-service apps
Industry-standard skillset
Simplify dev environments

What is Docker? 🐳

Docker is a platform that packages your application and all its dependencies into standardized, isolated units called containers.

Container Anatomy

📝 Your Application Code

📚 Dependencies & Libraries

⚙️ Runtime Environment

= 🐳 Complete Docker Container

Key Concept: Containers are lightweight, portable, and consistent across any environment—laptop, test server, or production cloud.

Essential Docker Commands

                
# Pull an image from Docker Hub
docker pull nginx:latest

# Run a container from an image
docker run -d -p 8080:80 --name my-nginx nginx:latest

# List running containers
docker ps

# Stop and remove a container
docker stop my-nginx && docker rm my-nginx

What is Docker Compose? 🎼

Docker Compose is a tool for defining and running multi-container Docker applications using a single YAML file.

Compose Orchestration

📄 docker-compose.yml

↓

🌐 Web App

🗄️ Database

⚡ Cache

Key Concept: Compose lets you define your entire application stack—web servers, databases, caches, queues—in one file and launch everything with one command.

Sample docker-compose.yml

1 version: '3.8'

2 services:

3 web:

4 image: nginx:latest

5 ports: ["8080:80"]

6 db:

7 image: postgres:14

                
# Start all services with one command
docker compose up -d

Knowledge Check 1

What is the primary purpose of Docker?

Feedback

Docker vs. Docker Compose: Key Differences 🔍

🐳 Docker (CLI)

📦

Single Container

Manual commands for each service

🎼 Docker Compose

📦📦📦

Multi-Container

One YAML file, one command

Aspect	Docker	Docker Compose
Scope	Single container management	Multi-container orchestration
Configuration	Command-line arguments	YAML file (declarative)
Networking	Manual network setup	Automatic network creation
Best For	Simple apps, single services	Complex multi-service stacks

Important: Docker Compose uses Docker under the hood. It's not a replacement—it's an abstraction layer that simplifies managing multiple containers.

Real-World Example: Blog Platform 📝

Let's compare how you'd run a typical three-tier blog application (web + database + cache).

❌ Docker: Multiple Commands

                        
docker network create blog-net
docker run -d --name db ...
docker run -d --name cache ...
docker run -d --name web ...

4 separate commands to remember

✅ Compose: Single Command

                        
services:
  web: ...
  db: ...
  cache: ...

docker compose up

Real Impact: Docker Compose automatically creates networks, manages startup order with depends_on, and lets services reference each other by name. What takes 10+ lines of Docker commands becomes 15 lines of declarative YAML.

Knowledge Check 2

When running multiple related containers (e.g., web app + database + cache), what is a key advantage of using Docker Compose?

Feedback

Decision Framework: When to Use What? 🎯

How many services does your app need?

↓

Just One

↓

🐳

Use Docker

Multiple

↓

🎼

Use Compose

Use Docker When:

✓ Running a single container
✓ Learning Docker fundamentals
✓ Testing individual microservices

Use Docker Compose When:

✓ Managing multiple services
✓ Setting up dev environments
✓ Onboarding new team members

Knowledge Check 3

Your team is building a web app with React frontend, Node.js API, PostgreSQL database, and Redis cache. Which tool is most appropriate for local development?

Feedback

Powerful Docker Compose Features 🚀

💾

Volume Persistence

Preserve data even when containers restart

🔐

Environment Variables

Manage configs and secrets safely

💚

Health Checks

Ensure services are ready before connecting

Volume Persistence Example

1 services:

2 db:

3 image: postgres:14

4 volumes:

5 - db-data:/var/lib/postgresql/data

Real Impact: These features eliminate hours of manual setup, making complex environments reproducible in seconds.

Knowledge Check 4

What does the depends_on field accomplish in a docker-compose.yml file?

Feedback

Common Pitfalls & Best Practices ⚠️

❌ Common Mistakes

Using Compose in production without orchestration (use Kubernetes/Swarm)

Hardcoding secrets in YAML files

Not using volumes for persistent data

Running containers as root user

✓ Best Practices

Use specific image tags (postgres:14.5 not :latest)

Keep Compose files in version control

Use .dockerignore to reduce build size

Implement health checks for all services

Industry Insight: According to Docker's 2023 survey, teams using Compose report 3x faster onboarding for new developers.

Quick Command Reference 📋

🐳 Docker Commands

                        
# Build & run
docker build -t app:v1 .
docker run -d -p 8080:80 app:v1

# Manage
docker ps
docker logs name
docker stop name
docker rm name
                        
                    

🎼 Compose Commands

                        
# Build & run
docker compose up -d
docker compose up --build

# Manage
docker compose ps
docker compose logs -f
docker compose down
                        
                    

Note: Modern Docker uses docker compose (no hyphen). The older docker-compose command is being phased out.

Ready to Test Your Knowledge? 🎯

You've learned the fundamentals of Docker and Docker Compose! Now it's time to demonstrate your understanding.

Assessment Details

5 multiple-choice questions
Real-world scenarios
Passing score: 80% (4/5 correct)
Certificate upon passing

Enter your name for the certificate:

Assessment Question 1 of 5

Which file format does Docker Compose use to define multi-container applications?

Assessment Question 2 of 5

You're joining a new team with an app that has 7 microservices. What's the best way to get the dev environment running on your laptop?

Assessment Question 3 of 5

What is the relationship between Docker and Docker Compose?

Assessment Question 4 of 5

Which scenario is BEST suited for using standard Docker commands rather than Docker Compose?

Assessment Question 5 of 5

In a docker-compose.yml file, what is the primary benefit of defining volumes for your database service?