Every great journey begins with a small step. In the Docker world, that step is running the Hello World container. Just like printing “Hello World” in programming languages proves your environment works, running this container validates your Docker installation and introduces you to the basic workflow.

Docker Foundations

1. What Happens When You Run docker run hello-world

• Step 1: Command Execution
  You type docker run hello-world in your terminal.
• Step 2: Image Lookup
  Docker checks if the hello-world image exists locally.
• Step 3: Image Pull
  If not found, Docker pulls the image from Docker Hub (the default registry).
• Step 4: Container Creation
  Docker creates a container from the image.
• Step 5: Execution
  The container runs a small program that prints a friendly message.
• Step 6: Exit
  The container stops after completing its task.

2. Why This Matters

• Demonstrates the client–daemon–registry–container workflow in action.
• Confirms Docker is installed and functioning correctly.
• Shows how lightweight containers can be - they start, run, and exit in seconds.

Things to Remember

• Containers are ephemeral by default: they run, complete their task, and stop.
• Docker Hub acts as the central library for images.
• The docker run command is the most fundamental way to interact with Docker.

Hands‑On Lab

Step 1: Run Hello World

docker run hello-world

Expected Output (simplified):

Hello from Docker!
This message shows that your installation appears to be working correctly.

Step 2: Inspect Containers

docker ps -a

• Shows the stopped hello-world container.

Step 3: Explore Images

docker images

• Displays the hello-world image pulled from Docker Hub.

Step 4: Remove the Image (Optional)

docker rmi hello-world

• Demonstrates how to clean up images.

Practice Exercise

1. Run docker run hello-world twice.
   • Observe that the second run is faster because the image is already cached locally.
2. Use docker ps -a to list containers and identify the hello-world container.
3. Remove the container and image, then rerun the command to see Docker pull the image again.

Visual Learning Model

docker run hello-world
   ↓
Docker Client → Docker Daemon → Registry (Docker Hub) → Image → Container → Output

The Hackers Notebook

Running Hello World with Docker is the first proof that your Docker setup works. It demonstrates the full lifecycle: command → image lookup → pull → container creation → execution → exit. This simple exercise builds confidence and sets the stage for running real applications in containers.