Docker - Public Repositories

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Docker public repositories are centralized locations for storing Docker images, which are essentially templates used in creating containers. These repositories make it easy to share and distribute containerized applications by providing an easy way for developers or users to access the pre-built software packages and download them. Public repositories are open to everyone; they often include a large list of images related to a variety of use cases, such as running popular operating systems like Ubuntu or CentOS or complex software stacks such as WordPress or Node.js.

The best example of a public repository is the Docker Hub, it acts as the default registry for Docker. This repository hosts a vast catalog of official and community-contributed images, with the ease of pulling and running them on any user's system. Public repositories facilitate collaboration and can speed up the pace of software development by allowing people to share preconfigured environments along with libraries and many other powerful tools.

Docker Public Repositories vs Private Repositories

Here's a one-on-one comparison highlighting the key differences between Docker Private Repositories and Public Repositories.

Popular Docker Public Repositories

In this section, lets have a look at the 3 most prominent and widely used public Docker repositories.

Docker Hub

Docker Hub is the default public registry for Docker. It's the most-used repository, containing a considerable amount of official images from well-known vendors and large numbers of community-contributed images.

Key Features

• Large Repository of Images − It offers an extensive repository of Docker images, including official images of popular software and a wide array of community-contributed images.
• Official Images − This offers a curated subset of high-quality images, which are maintained and kept updated by the software vendors themselves.
• Automated Builds − It provides the facility of automated builds, whereby you can trigger a build once your source repository has changed.
• Organizations and Teams − Enable collaboration and access control by using fine-grained features of creating organizations and managing teams.
• Webhooks − This will allow webhooks so that day-to-day integration with external services and tools is possible.

Red Hat Quay

Red Hat Quay is another popular enterprise-grade container registry for a secure and very scalable platform that can store, distribute, and manage containerized images.

Key Features

• Security and Compliance − It provides several robust security features, including vulnerability scanning, image signing, and role-based access control.
• Enterprise-Grade Scaling − Designed for high availability and the demands of large-scale container deployments.
• Image Scanning and Vulnerability Analysis − It supports comprehensive image scanning and vulnerability analysis through its integration with Clair.
• Geo-replication − It supports geo-replication which helps in disaster recovery and improves performance across different regions.
• Integration with the Red Hat Ecosystem − It integrates easily with other products and services in the Red Hat ecosystem.

GitHub Container Registry

GitHub Container Registry is an all-integrated container registry across GitHub for better convenience in storing and sharing container images close to your source code.

Key Features

• Tight Integration with GitHub − It helps manage your container images with ease alongside your code repositories.
• Anonymous Access to Public Images − It permits anonymous access to public images, easily accessible by anyone.
• Fine-Grained Permissions − Provides granular permissions to manage exactly who has access to your images.
• Automated Builds − Build automatically whenever changes in your code are made within your GitHub repositories.
• Interface familiar − A familiar GitHub-like interface to manage your container images.

Docker Commands to work with Public Repositories

Docker has a lot of commands that you can use to work with public repositories. With these commands, you can easily create, build, pull, tag, and push Docker images to the repository from your command line. Since Docker Hub is the most commonly used public repository, we will use it to demonstrate the important Docker commands to interact with repositories.

Creating a Dockerfile

Before you build an image, you need to create a Dockerfile, which is essentially just a text file containing the instructions or steps to create Docker images.

# Example Dockerfile
FROM ubuntu:latest
RUN apt-get update && apt-get install -y nginx
COPY index.html /var/www/html
CMD ["nginx", "-g", "daemon off;"]

Here, we pull the latest tagged Ubuntu image from the repository, install nginx and update the OS, copy the html files to the /var/www/html location, and run the nginx command.

Building the Docker Image

You can use the below docker build command to build a Docker image from the Dockerfile.

$ docker build -t my-nginx-image 

In the above command, we build a Docker image from the Dockerfile present in the current location specified by the dot at the end.

Creating a Docker Hub Account

To work and interact with the Dockerhub public repository, you need to create an account at Docker Hub.

Logging into Docker Hub

After you have created an account, you need to log in via the command line before pushing images to Docker Hub.

$ docker login

This will prompt you to verify your login credentials.

Tagging the Docker Image

When you tag a Docker image, it makes it easier to identify and manage multiple versions of Docker images. The tag format is username/repository:tag.

$ docker tag my-nginx-image myusername/my-nginx-image:latest

In the above command, we have tagged our my-nginx-image with the tag myusername/my-nginx-image:latest. You can use the docker images command to list all the images in your local now.

Pushing the Docker Image to Docker Hub

To push an image to Docker Hub, you can use the docker push command.

$ docker push myusername/my-nginx-image:latest

Pulling a Docker Image from Docker Hub

To pull an image from Docker Hub, you can use the docker pull command.

$ docker pull myusername/my-nginx-image:latest

Running a Docker Container from the Image

If you want to run a container from the pulled image, you can use the docker run command to spin up a container from that image.

$ docker run -d -p 80:80 myusername/my-nginx-image:latest

The above command runs a Docker container from the my-nginx-image in detached mode and with port 80 of the Docker container connected to port 80 of the host machine. This will allow you to access the nginx server page running in the container from your local browser.

Listing Docker Images

In order to list all Docker images on your local machine, you can use the docker images command.

$ docker images

Removing Docker Images

To remove a Docker image from your local machine, you can use the docker rmi command.

$ docker rmi myusername/my-nginx-image:latest

Can we use Public Docker Repositories for Production Applications?

Although public Docker repositories are convenient and have a great selection of images, using them for production applications can be risky because they might include untested or insecure images, which could make your application vulnerable to security threats. It is generally suggested that you should build and maintain the images on your own for production purposes after testing them properly to ensure that they adhere to the organizational security standards. However, public repositories would be useful while searching for base images or different technologies during development.

Conclusion

In this chapter, we have discussed how to work with Docker public repositories. We have understood the commands to create, tag, pull, push, and run containerized applications. We looked at the popular Docker public repositories and the features offered by each of them. The commands and processes outlined in this guide put forward an all-rounded framework for utilizing the power of Docker in facilitating containerization.