How to Containerize an Application.

Introduction

In today’s software development landscape, containerization has become an essential practice for building, deploying, and managing applications efficiently. This project focuses on containerizing a simple Node.js Todo List Manager application using Docker. By packaging the application and its dependencies into a container, developers can ensure consistency across different environments, simplify deployment, and improve scalability. Whether you're new to Docker or just getting started with containerization, this project offers a hands-on experience that demonstrates how to move an application from a local environment to a portable, containerized setup.

Prerequisites

Before you begin, ensure you have the following installed and set up on your system:

• Docker Desktop (latest version) – to build, run, and manage containers.
• Git client – to clone the project repository and manage source control.
• An IDE or text editor – such as Visual Studio Code, for editing and managing project files.
• (Optional but recommended) Basic understanding of terminal or command-line operations.

Step 1 : Get the app

• Steps to Get the App and Run it in Visual Studio Code
• Open Visual Studio Code
• Launch VS Code on your computer.

• Open the Terminal
• Click on Terminal at the top menu and select new terminal

• Clone the Application Repository
• In the terminal, type the following command and press Enter:

git clone https://github.com/docker/getting-started-app.git

• Navigate into the App Folder cd getting-started-app
• Open the Folder in VS Code (Optional) code .

• View the contents of the cloned repository. You should see the following files and sub-directories.

Step 2 : Build image

To build the image, you'll need to use a Dockerfile. A Dockerfile is simply a text-based file with no file extension that contains a script of instructions. Docker uses this script to build a container image.

• In the getting-started-app directory, the same location as the package.json file, create a file named Dockerfile with the following contents:

• This Dockerfile starts off with a node:lts-alpine base image, a light-weight Linux image that comes with Node.js and the Yarn package manager pre-installed. It copies all of the source code into the image, installs the necessary dependencies, and starts the application.

• Build the image using the following commands:

docker build -t getting-started-app .

Step 3: Start an app container

• Now that you have an image, you can run the application in a container using the docker run command.
• Run your container using the docker run command and specify the name of the image you just created:

** docker run -d -p 127.0.0.1:3000:3000 getting-started**

• After a few seconds, open your web browser to http://localhost:3000. You should see your app.

Conclusion

By the end of this project, you will have successfully transformed a simple Node.js Todo List Manager into a fully containerized application. You’ll gain hands-on experience with Docker commands, image creation, and container management — valuable skills for modern DevOps and cloud-based development workflows. This exercise not only strengthens your understanding of containerization but also prepares you to deploy scalable, portable, and efficient applications in real-world environments.