Docker Image: Creating and Managing Container Images

Docker images are lightweight, standalone, executable packages that include everything needed to run a piece of software, including the code, runtime, libraries, environment variables, and config files. They provide a portable and consistent way to deploy applications across different environments in Docker containers.

Containerization has revolutionized software development and deployment, providing developers with a flexible and efficient way to package and distribute applications. Docker, a popular containerization platform, offers powerful tools for creating, pulling, and managing container images. Docker images serve as the building blocks for containers, encapsulating everything an application needs to run consistently across different environments. In this article, we will explore the process of creating, pulling, and managing Docker container images.

Must Explore: Docker Online Courses & Certifications

Table of Content

• What are Docker Images? 
• Prerequisite: Docker Installation
• Cloning a Sample React-Docker App
• Creating Docker Images
• Pulling Docker Images
• Managing Docker Images
• Image Versioning and Tagging Strategies
• Best Practices for Docker Images

What are Docker Images?

Docker images are lightweight, self-contained, and executable software packages. They contain everything needed to run an application, including its code, runtime environment, system tools, libraries, and dependencies. One of the key features of Docker images is their layered architecture. Each layer represents a specific change or modification to the base image, providing a mechanism for reusability and efficiency.

Prerequisite: Docker Installation

Before you can start creating and managing Docker images, you need to have Docker installed on your system. 

Follow the steps below to install Docker based on your operating system:

Windows:

Visit the official Docker website: https://www.docker.com/products/docker -desktop.

Click on the "Get Docker" button to download the Docker Desktop installer.

Run the installer and follow the on-screen instructions.

Once the installation is complete, Docker will run on your Windows machine.

Mac:

Go to the official Docker website: https://www.docker.com/products/docker- desktop.

Click on the "Get Docker" button to download the Docker Desktop installer.

Open the downloaded DMG file and drag the Docker icon to the Applications folder.

Launch Docker from the Applications folder.

Docker will be installed and running on your Mac.

Linux:

Docker provides different installation methods for various Linux distributions. Refer to the official Docker documentation for detailed installation steps based on your Linux distribution: https://docs.docker.com/engine /install/.

Note: For Linux systems, ensure you have the necessary permissions to install Docker or run the Docker commands with root or sudo access.

Once Docker is installed, you can verify the installation by opening a terminal or command prompt and running the following command:

This command will display the Docker client and server versions, indicating a successful installation.

Ensure that Docker is running in the background before proceeding with the Docker image creation, pulling, and management steps outlined in this article.

Cloning a Sample React-Docker App

Let's start by cloning a sample React-Docker app from a GitHub repository to demonstrate the process of creating a Docker image. This app will serve as our example throughout the article.

Open your terminal or command prompt.

Change to the directory where you want to clone the repository.

Run the following command to clone the repository:

Once the repository is cloned, navigate to the project directory:

Now that we have the sample React-Docker app cloned locally, we can create a Docker image for it.

Creating Docker Images

Creating Docker images allows developers to package their applications and dependencies into a single, portable unit. The process begins with a Dockerfile, a text file containing instructions on how to build the image. 

Let's look at an example Dockerfile for a simple React.js application:

Note: This Dockerfile already exists in the cloned repository. You don't need to create again.

To build the Docker image, navigate to the directory containing the Dockerfile and run the following command:

This command builds the Docker image and tags it with the name my-react-app. Make sure to include the. at the end, which indicates that the build context is the current directory.

To verify the successful creation of the image, execute the following command:

You can see the “my-react-docker-app” image.

Once the image is built, you can run a container based on that image using the following command:

This command starts a new container and maps port 3000 of the container to port 3000 of your local machine.

Open your web browser and visit http://localhost:3000 to see your React app running in the Docker container.

Note: This Dockerfile assumes that your React app has a build script defined in the package.json file, which is commonly used in React projects. If your project has a different setup, you might need to modify the Dockerfile accordingly.

Pulling Docker Images

Pulling Docker images is the act of retrieving pre-built images from a remote registry. Docker Hub, the default registry provided by Docker, hosts an extensive collection of public images. To pull an image, developers use the docker pull command followed by the image name and, optionally, the tag, representing a specific version or variant of the image. For example, to pull the official Node.js image with the latest version, run the following command:

To confirm the successful retrieval of the image, run:

Managing Docker Images

Effective management becomes crucial as the number of Docker images in an environment grows. Docker provides various commands to simplify image management. The docker images command lists all the images available on the host machine, displaying their repository, tag, and size. However, before removing an image, it is important to stop and remove any running 140129 using it.

To stop a container, you can use the docker stop command followed by the container name or container ID.

To find the container name or container ID, run

Finally, to remove an image, you can use the docker rmi command followed by the image name or image ID. For example, to remove an image with the tag my-react-docker-app, run:

Image Versioning and Tagging Strategies

Versioning and tagging play a crucial role in managing Docker images effectively. Versioning helps track different iterations and updates of an image, providing a history of changes. It is essential to use meaningful labels and tags when tagging images, making identifying specific versions or variants easier. Following a consistent and standardized tagging strategy simplifies image retrieval and ensures compatibility between different components.

Here's an example of how to tag a Docker image with a version:

Build your Docker image with a specific version number:

Tag the image with a new version:

To Verify, run:

Best Practices for Docker Images

It is important to follow best practices to ensure efficient and secure use of Docker images. 

1. Use Official Base Images:

     Pull official base images from trusted sources:

2. Keep Images Lightweight:

Exclude unnecessary files and dependencies from the image:

Create a .dockerignore file in the same directory as the Dockerfile to specify files and directories to exclude during the build process.

Example .dockerignore file:

In this example, we exclude the node_modules directory, npm-debug.log file, and.DS_Store file from the image build context. These files are commonly generated during development or are platform-specific and not needed in the final image.

Using a .dockerignore file can significantly reduce the build context size and exclude unnecessary files, resulting in smaller and more efficient Docker images.

It's important to create and place the .dockerignore file in the same directory as the Dockerfile before running the docker build command.

3. Regularly Update Images:

Update images to incorporate the latest security patches and bug fixes:

4. Implement Image Scanning:

Use image scanning tools to identify vulnerabilities in the images:

Example using Docker Security Scanning:

Following these best practices ensures the efficient and secure use of Docker images. Using official base images, minimizing image size, regularly updating images, and implementing image scanning tools contribute to a robust and secure container environment.

Conclusion

Docker images are pivotal in the world of containerization, enabling developers to package and distribute applications seamlessly. This article explored the process of creating, pulling, and managing Docker container images. Developers can define and build images encapsulating their applications and dependencies by cloning a sample React-Docker app and leveraging Dockerfiles and the Docker CLI. Pulling images from Docker Hub allows developers to access pre-built images, streamlining the development process. Effective management, adherence to best practices, and advanced image management techniques contribute to a robust and scalable container environment, maximizing the benefits of Docker image usage.

Contributed by: Anish Lohiya