| JNTech

Understand Docker Images and Containers

Before creating our own application, let's understand two important Docker concepts.

1. What is a Docker Image?

A Docker Image is a read-only template containing everything required to run an application.

For example:

Application code
Runtime (such as .NET)
Dependencies
Configuration

Think of an image as a blueprint.

2. What is a Docker Container?

A Docker Container is a running instance of a Docker Image.

Think of it this way:

Image = Blueprint
Container = Running application created from that blueprint.

3. Practical Exercise

Open Command Prompt and execute the following commands one by one.

Command 1: List Docker Images

docker images

This displays downloaded images.

Command 2: List Running Containers

docker ps

This displays currently running containers.

Command 3: List All Containers

docker ps -a

This displays running and stopped containers.

Command 4: Download an Nginx Image

docker pull nginx

Nginx is a web server. Docker downloads its image from Docker Hub.

Command 5: Verify the Image

docker images

You should now see nginx in the image list.

Expected learning outcome

You should now understand:

Command	Purpose
`docker images`	List images
`docker ps`	List running containers
`docker ps -a`	List all containers
`docker pull nginx`	Download an image

Create and Run Your First Docker Container

Objective: Run an Nginx web server inside a Docker container and access it through your Windows browser.

1. Create an Nginx Container

Open Command Prompt and execute:

docker run -d -p 8080:80 --name my-nginx nginx

Explanation:

Parameter	Description
`docker run`	Creates and starts a container
`-d`	Runs in background (detached mode)
`-p 8080:80`	Maps Windows port 8080 to container port 80
`--name my-nginx`	Assigns a container name
`nginx`	Docker image name

2. Verify the Container

Execute:

docker ps

You should see something similar to:

CONTAINER ID   IMAGE   COMMAND   STATUS
xxxxxxxx       nginx   ...       Up ...

3. Access Nginx from Browser

Open Google Chrome or Edge.

Navigate to:

http://localhost:8080

Exploring Microsoft Radius Application Platform - The New Stack

You should see:

Welcome to nginx!

Congratulations! You have successfully deployed a web server inside a Docker container.

4. Stop the Container

Execute:

docker stop my-nginx

Refresh your browser. The website should no longer be accessible.

5. Start the Container Again

docker start my-nginx

Refresh the browser. Nginx should work again.

Commands learned

Command	Purpose
`docker run`	Create and run container
`docker ps`	Check running containers
`docker stop`	Stop container
`docker start`	Start stopped container