cli-demo

Containerisation CLI Demo

A quick live-demo walkthrough showing the power of containers using Docker CLI and Docker Compose.

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1. Instant Web Server

Start an NGINX web server in seconds:

docker run --detach --publish 8080:80 --name web nginx

Open in browser:

http://localhost:8080

Observations

• No installation required
• No config files
• No service management
• Works instantly on a clean machine

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2. PostgreSQL Database in Seconds

Start PostgreSQL:

docker run -d \
  -e POSTGRES_PASSWORD=secret \
  -p 5432:5432 \
  --name db \
  postgres

Confirm it's up and accepting connections:

docker logs db
telnet 127.0.0.1 5432

Observations

• Fully initialized database in seconds
• No apt install or manual setup
• Disposable infrastructure

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3. Throwaway Runtimes (Node, Python, JDK)

Run a temporary Node.js environment:

docker run --rm -it node node

ℹ️ -it is short for --interactive --tty

Inside Node REPL:

console.log("Hello from a clean runtime");
[1,2,3].map(x => x * 2)

Exit the container:

.exit

Observations

• No Node.js installed locally
• No environment pollution
• Disposable tooling

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4. Multiple Runtime Versions Side-by-Side

Python

docker run --rm python:3.8 python --version
docker run --rm python:3.12 python --version

Multiple JDK versions side-by-side

# NOTE: eclipse-temurin = OpenJDK binaries
docker run --rm eclipse-temurin:17 java -version
docker run --rm eclipse-temurin:21 java -version
docker run --rm eclipse-temurin:latest java -version

Observations

• Multiple versions simultaneously
• No dependency conflicts
• Perfect reproducibility

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5. WordPress + Database

Create Network

docker network create wp-net

Start MySQL

docker run -d \
  --name wp-db \
  --network wp-net \
  -e MYSQL_ROOT_PASSWORD=secret \
  -e MYSQL_DATABASE=wordpress \
  -e MYSQL_USER=wp \
  -e MYSQL_PASSWORD=wp \
  mysql:8

Start WordPress

docker run -d \
  --name wp \
  --network wp-net \
  -p 8081:80 \
  -e WORDPRESS_DB_HOST=wp-db:3306 \
  -e WORDPRESS_DB_USER=wp \
  -e WORDPRESS_DB_PASSWORD=wp \
  -e WORDPRESS_DB_NAME=wordpress \
  wordpress

Open in browser:

http://localhost:8081

Observations

• Multiple services connected instantly
• Automatic service discovery
• Environment-based configuration
• No manual database wiring

BONUS: Can we persist our infrastructure commands?

These Docker commands setup our infrastructure consistently, but wouldn't it be nice if we could persist these as a configuration file? This is where Docker Compose comes in!

The commands above have been persisted as compose.yml, and can all be brought up with a simple docker compose up --detach command.

This is called 🌟 Infrastructure as Code 🌟

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6. Docker Compose Example

A full JVM application + database stack — Spring Boot + Postgres — defined entirely in a single compose.yaml. No local JDK, no local Postgres, just one command.

See edu-spring-postgres/README.md for the walkthrough and commands.

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7. Volume mounting

We can mount in volumes using the CLI with the --volume or -v argument.

Volumes can be either relative or absolute paths on your machine - or the name of a docker volume.

Example:

docker run --volume ./web:/usr/share/nginx/html --detach --publish 8080:80 --name web nginx

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8. Cleanup

Remove containers:

docker rm --force web db wp wp-db spring-app spring-db

Remove networks:

docker network rm wp-net spring-net

Remove compose stack (and data volumes!):

docker compose down --volumes

General cleanup of all unused Docker resources

docker system prune

Observations

• No leftover configuration
• No config drift
• Fully disposable environments

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8. Key Takeaways

• Containers package the entire runtime environment
• Same image runs everywhere
• No "works on my machine"
• Fast local development setup
• Easy reproducibility
• Infrastructure becomes disposable
• Consistent deployments across environments