Install and Use Docker on Rocky Linux 9: A Beginner's Guide

8 min read 14-11-2024

Install and Use Docker on Rocky Linux 9: A Beginner's Guide

Docker is a powerful tool that enables developers to package and run applications in isolated environments called containers. These containers are lightweight and portable, allowing applications to run consistently across different environments, from development to production. Rocky Linux, a community-driven, enterprise-grade operating system, provides a stable and reliable platform for running Docker. This comprehensive guide will walk you through the process of installing and using Docker on Rocky Linux 9, from basic setup to advanced configurations.

Understanding Docker and Its Benefits

Docker utilizes a client-server architecture, where the Docker client interacts with the Docker daemon, which manages containers on the host machine. We'll dive into this architecture later in the guide. But first, let's understand why Docker is so popular:

Portability: Docker containers are independent of the underlying operating system, making them easily transferable between different environments. This means an application built on a developer's machine can be seamlessly deployed to a production server without compatibility issues.
Efficiency: Docker containers are lightweight and resource-efficient, requiring only the necessary dependencies and binaries to run. This translates to faster startup times and lower resource consumption compared to traditional virtual machines.
Isolation: Each Docker container operates in its own isolated environment, preventing conflicts and ensuring that applications are not affected by changes made to other containers or the host system.
Scalability: Docker allows for easy scaling of applications by creating multiple instances of containers. This makes it ideal for handling fluctuating workloads and ensures that applications can be quickly scaled up or down as needed.
Reproducibility: Docker containers offer reproducible builds, meaning that a container can be recreated with the same configuration and dependencies on any machine. This eliminates the "it works on my machine" problem and ensures consistency across development, testing, and production environments.

Installing Docker on Rocky Linux 9

Installing Docker on Rocky Linux is a straightforward process. Follow these steps:

Update your system: Before installing Docker, ensure your system is up to date by running the following command:
```
sudo dnf update
```
Install necessary packages: Docker requires several dependencies, including the yum-utils package. Install them using:
```
sudo dnf install yum-utils
```

Set up the Docker repository: Add the Docker repository to your system's package manager:

sudo dnf install -y dnf-plugins-core
sudo dnf config-manager --add-repo https://download.docker.com/linux/centos/docker-ce.repo

Install Docker Engine: Once the repository is added, install Docker Engine:
```
sudo dnf install docker-ce docker-ce-cli containerd.io
```
Start and enable the Docker service: After installation, start the Docker service:
```
sudo systemctl start docker
```
To ensure Docker starts automatically at system boot, enable the service:
```
sudo systemctl enable docker
```
Verify the installation: To check if Docker is installed and running correctly, run the following command:
```
sudo docker version
```
This will display information about the Docker client and server versions.

Using Docker: A Hands-On Example

Now that Docker is installed, let's explore its capabilities by running a simple example. We will use a readily available Nginx image to host a basic web server.

Search for an image: To find a suitable image, use the docker search command. In this case, we want an Nginx image:
```
docker search nginx
```
This will return a list of Nginx images available on Docker Hub, a registry of Docker images.
Pull the image: Choose an appropriate Nginx image from the search results and pull it to your local machine using the docker pull command. For example, we'll pull the official Nginx image:
```
docker pull nginx:latest
```
Run the container: Now, let's run the pulled Nginx image in a container. We'll map port 80 of the container to port 8080 on the host machine for access:
```
docker run -d -p 8080:80 nginx:latest
```
The -d flag runs the container in detached mode, keeping it running in the background. The -p flag maps ports.
Access the web server: Open your web browser and navigate to http://localhost:8080. You should see the Nginx welcome page, indicating that the container is running successfully.

Understanding the Docker Architecture

To better grasp Docker's functionality, let's delve into its architecture. Docker consists of three main components:

Docker Client: This is the interface through which users interact with Docker. It sends commands to the Docker daemon, which then manages the container lifecycle.
Docker Daemon: The Docker daemon is a background process that runs on the host machine. It manages images, containers, networks, and volumes.
Docker Registry: A Docker registry is a centralized repository for storing and distributing Docker images. The most popular registry is Docker Hub, which offers both public and private image repositories.

Managing Docker Images

Docker images are the building blocks of Docker containers. They contain all the necessary files, libraries, and dependencies to run an application. Managing Docker images is crucial for efficient containerization. Here's a rundown of essential commands:

Listing Images: View all images on your system with the docker images command. This will display information about the image name, tag, size, and creation date.
Pulling Images: To obtain images from a registry, use the docker pull command. This will download the specified image to your local machine.
Deleting Images: Remove images from your system using the docker image rm command. Be cautious, as this will permanently delete the image.
Building Images: Create your own custom Docker images using the docker build command. This involves specifying a Dockerfile, which defines the steps required to build the image.

Managing Docker Containers

Docker containers are the running instances of Docker images. They encapsulate the application and all its dependencies, making them lightweight and portable. Managing containers is essential for day-to-day Docker usage. Key commands include:

Listing Containers: View all running and stopped containers using the docker ps command. Use the -a flag to list all containers, regardless of their status.
Running Containers: Start a container from an image using the docker run command. You can specify various options, such as port mappings, volume mounts, and environment variables.
Stopping Containers: Gracefully halt a running container using the docker stop command.
Restarting Containers: Start a stopped container using the docker start command.
Deleting Containers: Remove a container using the docker rm command.

Advanced Docker Concepts

Docker Networking

Docker uses a custom networking system to manage communication between containers and the host machine. Understanding Docker networking is crucial for creating complex applications and managing communication between different containers. Here's a breakdown of key concepts:

Bridge Network: This is the default Docker network. Containers on the bridge network can communicate with each other, but not directly with the host machine.
Host Network: Containers on the host network share the host's networking namespace. This allows containers to access services directly on the host machine.
None Network: Containers on the none network have no networking capabilities. This is useful when creating isolated containers or when you want to control networking manually.
Overlay Network: Overlay networks enable communication between containers across different hosts. This is particularly useful for running distributed applications.

Docker Volumes

Docker volumes provide a persistent way to store data associated with containers. This is crucial for scenarios where data needs to persist even when the container is deleted or restarted. Volumes can be either named or anonymous.

Named Volumes: Named volumes are explicitly created and can be managed independently of containers. This provides flexibility and allows you to easily share data between containers.
Anonymous Volumes: Anonymous volumes are automatically created when a container is started. They are tied to the container and are deleted when the container is removed.

Docker Compose

Docker Compose is a tool for defining and managing multi-container Docker applications. It uses a YAML file called docker-compose.yml to describe the services, networks, and volumes that make up your application. This simplifies the deployment and management of complex applications.

Real-World Applications of Docker

Docker has revolutionized the way applications are developed and deployed. Here are a few real-world examples of how Docker is used:

Web Development: Docker is widely used for building and deploying web applications. Developers can create containers that bundle all the necessary components, such as web servers, databases, and application code, ensuring consistency across environments.
Microservices Architecture: Docker is a cornerstone of microservices architecture, allowing developers to create and deploy independent services that can be scaled and managed individually.
DevOps Automation: Docker integrates seamlessly with DevOps workflows, facilitating automated builds, testing, and deployment. This helps accelerate software development and reduce manual errors.
Machine Learning: Docker is used in machine learning workflows for packaging and deploying models, dependencies, and runtime environments, ensuring consistency and reproducibility.
Data Science: Docker simplifies the deployment and sharing of data science projects, enabling users to easily replicate results and collaborate effectively.

Docker Security Considerations

While Docker offers numerous advantages, it's essential to address security concerns. Here are some key considerations:

Image Security: Use trusted images from reputable sources like Docker Hub. Scan images for vulnerabilities before deploying them.
Container Security: Restrict container access to resources they need. Limit user privileges within containers.
Network Security: Use Docker's built-in networking features to isolate containers and restrict communication.
Docker Daemon Security: Configure the Docker daemon to limit access and restrict potential attack vectors.

FAQs

Here are answers to some frequently asked questions about Docker:

1. What is the difference between Docker and a virtual machine?

While both Docker and virtual machines provide isolation and portability, they differ in their approach. Virtual machines emulate the entire hardware and operating system, while Docker containers share the host operating system's kernel and resources. This makes Docker containers significantly lighter and more efficient.

2. Why should I use Docker?

Docker provides numerous benefits, including portability, efficiency, isolation, scalability, and reproducibility. It simplifies the deployment and management of applications, ensuring consistency across environments.

3. Is Docker difficult to learn?

No, Docker is relatively easy to learn, especially for beginners. With numerous online resources and tutorials, getting started with Docker is straightforward.

4. What are some common Docker commands?

Here are some common Docker commands:

docker run: Run a container from an image.
docker ps: List running containers.
docker stop: Stop a running container.
docker start: Start a stopped container.
docker rm: Remove a container.
docker images: List Docker images.
docker pull: Pull an image from a registry.
docker push: Push an image to a registry.

5. What are some alternative containerization technologies?

While Docker is the most popular containerization technology, there are other alternatives, such as:

Podman: A container runtime that is compatible with Docker images but offers improved security and performance.
LXD: A container management tool that provides a more traditional approach to containerization, closer to virtual machines.
rkt: A container runtime developed by CoreOS.

Conclusion

Docker is a powerful tool that has transformed the way we build, deploy, and manage applications. Its ability to create lightweight, portable, and isolated environments has made it a popular choice for developers and DevOps professionals. In this guide, we have covered the fundamentals of installing and using Docker on Rocky Linux 9. From basic setup to advanced concepts, we have explored various aspects of Docker to help you get started and harness its power to create and deploy applications efficiently. Docker continues to evolve with new features and enhancements, making it an essential technology for any modern software development workflow.