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how does docker containerization work?

By September 13, 2023November 3rd, 2023Azure, Blogs, Cloud, DevOps
docker containerization


Welcome to our beginner’s guide on Docker! If we’re new to software development, Docker is a handy tool that makes life easier. In this blog, we’ll cover the basics of Docker, including what it is and why it’s useful. We’ll also talk about Docker images, which are like application packages. We’ll learn about the Docker registry, where we can find and share these images. We’ll introduce Docker files, which are instructions for creating Docker images. We’ll even show you some simple commands to get started. By the end of this guide, we’ll have a good understanding of Docker and how it simplifies deploying applications. Let’s dive in and explore the world of Docker together!

Why do Developers prefer Docker over virtual machines?

When it comes to application development, Docker has captured the hearts of developers worldwide, and it’s no wonder why! Let’s explore the top reasons why Docker has become the go-to choose, leaving traditional virtual machines in the dust.


    1. Efficiency: Docker containers consume fewer resources and booting up at lightning speed. With Docker, developers enjoy faster startup times and optimized resource utilization, resulting in a smoother and more efficient development experience.
    2. Seamless Portability: Imagine being able to effortlessly transport your applications across different systems, without worrying about compatibility issues. Docker makes it possible! By providing a consistent runtime environment, Docker empowers developers to package and deploy applications across various systems that support Docker.
    3. Fast Deployment: Today’s computer world, the speed of software development is very important. Docker understands this need for agility. With Docker, developers can easily deploy applications and testing during the development process.
    4. Scaling Made Simple: As applications grow in complexity and demand, scalability becomes a crucial factor. Docker’s containerization approach makes scaling a cakewalk. By effortlessly managing and orchestrating containers across multiple machines, Docker allows developers to easily adapt and expand their applications as needed.
    5. Isolation and Security: Security is a top priority for developers, and Docker takes it seriously. Docker ensures application isolation, shielding applications. Additionally, Docker provides built-in security features that further enhance application protection. With Docker, developers can rest easy knowing their applications are well-guarded.


What Problems does Docker solve?

Docker is a powerful platform that solves the problem of software application deployment and management by utilizing containerization technology. Traditional software deployment often involves complex and time-consuming processes, such as configuring the runtime environment, managing dependencies, and dealing with compatibility issues across different systems. Docker simplifies this process by encapsulating an application and its dependencies into a lightweight, standalone container.

By using Docker, developers can package their applications with all the necessary components, including the operating system, libraries, and dependencies, into a standardized container format. These containers are isolated and provide consistent runtime environments across different machines, whether it’s a developer’s local workstation, a testing environment, or a production server. Docker containers can run on any system that supports Docker, making applications highly portable and reducing the chances of compatibility issues.

Another problem Docker solves is the efficient utilization of system resources. Traditional virtualization technologies require running separate operating system instances for each application, leading to resource inefficiencies. Docker containers, on the other hand, share the host operating system kernel, enabling higher density and better resource utilization. Multiple containers can run simultaneously on the same machine without the overhead of running separate virtual machines, optimizing resource allocation, and minimizing hardware costs.

Additionally, Docker enables easier collaboration among development teams. With Docker, developers can share their application containers, ensuring that everyone works with the same software stack and dependencies. This eliminates the “it works on my machine” problem, as containers provide a consistent environment regardless of the underlying infrastructure. Docker also supports versioning and allows for easy distribution of container images, facilitating seamless integration into continuous integration and deployment workflow.

Docker Concept:
1. Docker Image and container:
Imagine a magical box called a Docker image. It holds everything you need to make an application work smoothly, like the code, tools, and even its friends (dependencies). You can think of a Docker image as a blueprint for creating special containers. These containers are like little worlds of their own, where your application can run safely and consistently. The best part is that Docker images are lightweight, so they’re easy to move around and share with others. It’s like packing up your app and sending it on a grand adventure to any computer you want.

2. Docker Registry: A Docker registry acts as the central repository to store docker images. It acts as a storage and distribution platform where developers can publish their Docker images and other users can discover, access, and pull those images to their local environments. Docker Hub is the most widely used public Docker registry, but organizations can also set up private registries for internal use, ensuring secure storage and controlled access to Docker images.

3. Docker file: A Docker file is a crucial component in the world of Docker containers. It is a plain text file that contains a series of instructions, or steps, to build a Docker image. These instructions outline the exact steps needed to create a containerized application environment.

The Docker file starts with a base image, which serves as the foundation for the container. This base image can be a minimalistic operating system or an existing image with pre-installed software. From there, the Docker file allows you to define and customize the container to suit your specific application requirements.

Each instruction in the Docker file represents a layer in the image’s construction. Layers are like building blocks that stack on top of each other to form the final image. Docker optimizes this layering approach by reusing existing layers whenever possible, resulting in faster and more efficient image builds.

Docker file instructions can perform a wide range of tasks, including installing software packages, copying files into the image, setting environment variables, and configuring the container’s runtime behavior. These instructions can be written in a clear and straightforward syntax, making it easy for developers to understand and modify the Docker file as needed.

One of the significant advantages of Docker files is their portability. Once you have a Docker file, you can easily share it with others, allowing them to recreate the exact same container environment. This consistency ensures that applications behave the same way across different development, testing, and production environments.

Docker files also enable version control and collaboration. By keeping Docker files in a version control system like Git, you can track changes, roll back to previous versions, and collaborate with team members effectively. This makes it easier to maintain and update container environments as your application evolves.

In summary, a Docker file is a powerful tool for building Docker images. It provides a clear and structured approach to defining the steps needed to create a containerized environment for your applications. With Docker files, you can achieve consistency, portability, and scalability, simplifying the process of packaging, deploying, and maintaining containerized applications.

4. Sample Docker Command: Docker offers easy and helpful commands to work with containers and images. These commands make it simple to manage containers, build and run images, and configure networks and storage. docker run: Use this command to start a new container from an image. You can specify options like the image to use, network settings, and environment variables. For example,

docker run -d -p 8080:80 nginx starts a background container running the NGINX web server, accessible at port 8080 on your computer.

docker stop: When you want to stop a running container, use docker stop followed by the container ID or name. It gently stops the container by sending a signal. For instance,

docker stop my-container stops a container named “my-container”.

docker build: This command creates a Docker image from a Docker file. By default, it looks for a file named “Dockerfile” in the current directory. We can use the -f flag to specify a different Docker file name. For example, docker build -t my-image:1.0. builds an image named “my-image” with version “1.0” using the Docker file in the current directory.

docker ps: To see a list of running containers, use docker ps. It shows details like container ID, used image, status, and exposed ports. Adding the -a flag displays all containers, even if they’re not currently running.

docker rm: When you’re done with a container, you can remove it using docker rm followed by the container ID or name. If the container is running, either stop it first or use the -f flag to force removal. For example, docker rm my-container removes a container named “my-container”.

These commands are just the beginning. Docker offers many more commands to manage containers and images, making it easier to develop, deploy, and maintain applications within a containerized environment.

Sample Docker Project:

Here’s an example project that demonstrates how to containerize a “Hello World” Angular application using Docker.

First, let’s create a new directory for the angular project:


Next, we’ll initialize a new Angular project using the Angular CLI:


Now, create a simple “Hello World” Angular component. Open the file src/app/app.component.html and replace below contents with old.:


We’re almost ready to Dockerize our Angular application. Let’s create a Docker file. Create a file called Docker file in the root of your project directory and open it with a text editor.

Here’s the content of the Docker file:



This Docker file consists of two stages and is used to build and serve an Angular application using Docker.

Let’s go through each section in detail:

Stage 1: Build the Angular application.

In this stage, we are using a base image node:14 as the build environment for the Angular application. Here’s what each line does:

FROM node:14 as build: This sets the base image as node:14 and assigns a name build to this stage. The base image provides the necessary dependencies and tools to build a Node.js application.

WORKDIR /app: This sets the working directory inside the container as /app. It will be the location where the application’s code and files will be copied.

COPY package*.json ./: This copies the package.json and package-lock.json files from the host machine (the directory where the Docker file is located) to the /app directory inside the container. This allows Docker to cache the dependencies installation step separately from the application code, optimizing the build process.

RUN npm install: This runs the npm install command in the container, which installs the dependencies Mentioned in the package.json file.

COPY. .: This copies all the remaining files and directories from the host machine to the /app directory inside the container. This includes the application source code.

RUN npm run build –prod: This command executes the build script defined in the package.json file. It builds the Angular application with the –prod flag, indicating that it should be built for production with optimizations.

At this stage, the Angular application is built and ready to be served.

Stage 2: Serve the application with a lightweight HTTP server.

In this stage, we are using a lightweight web server image nginx:alpine to serve the Angular application. Here’s what each line does:

FROM nginx:alpine: This sets the base image as nginx:alpine, which provides a minimal Nginx server installation.

COPY –from=build /app/dist/hello-world-angular /usr/share/nginx/html: This copies the built Angular application from the build stage to the /usr/share/nginx/html directory inside the container. The hello-world-angular folder is the output of the Angular build process and contains the static files needed to serve the application.

EXPOSE 80: This exposes port 80 of the container, allowing external access to the Nginx server running inside.

CMD [“nginx”, “-g”, “daemon off;”]: This specifies the command to run when the container starts. It starts the Nginx server and keeps the container running in the foreground with the daemon off; directive.

When the Docker image is built and a container is created from it, the Angular application will be served by the Nginx server on port 80. Users can access the application by visiting the appropriate URL or IP address.

Once you have created and saved the Docker file, it’s time to build the Docker image. Open a terminal, navigate to the root of your project directory, and run the following command:


This command builds a Docker image using the Docker file in the current directory and tags it with the name hello-world-angular.

After the build process completes successfully, we can run a container based on our newly created image:


This command runs a container based on the hello-world-angular image and maps port 8080 of the host to port 80 of the container. You can choose a different port if desired.

Now, if you open your web browser and navigate to http://localhost:8080, you should see the “Hello, World!” message entered by your Angular application running inside a Docker container.

That’s it! You have successfully containerized a “Hello World” Angular application using Docker.


In conclusion, Docker has become an essential tool in the world of software development and deployment. Its benefits and the problems it resolves make it an indispensable part of modern application development workflows. Docker provides a consistent and isolated environment through its containerization technology, allowing applications to run reliably across different systems. With Docker, developers can package their applications into Docker images, which include all the dependencies and configurations needed for smooth execution. These images can be easily shared and deployed on any machine running Docker, thanks to Docker’s lightweight and portable nature. Docker also provides a centralized repository called Docker Registry, where developers can store and distribute their Docker images.

In this article, we explored the reasons why Docker is widely used, including its efficiency, scalability, and reproducibility. We discussed the benefits of Docker, such as improved resource utilization, simplified deployment, and faster development cycles. We also touched upon the problems Docker resolves, such as dependency management, environment inconsistencies, and application portability.

To illustrate the concepts discussed, we walked through a sample Angular project that was Dockerized. We created a Docker file that defined the build and serving stages of our Angular application. We used Docker commands to build a Docker image and run a container based on that image. By containerizing our application, we achieved easy deployment and execution in a consistent environment.

Overall, Docker revolutionizes the way we develop, deploy, and manage applications. It empowers developers with the ability to build, package, and distribute applications as self-contained units, ensuring consistent and reliable execution across various environments. By leveraging Docker’s containerization technology, developers can streamline their workflows, collaborate more effectively, and deliver software faster than ever before.

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