What Is a Docker Registry? An Overview

If not diving into all the details, then Docker Registry is needed to distribute containerized apps in a secure, simple, and what is most importantly the scalable way.

In the article, you will get more information regarding Docker Registry, its setup, usage, and some recommendations regarding its functioning.

Understanding docker registry

There are 2 different ways in which the Docker registry term can be understood. When talking about a narrower concept, this is a tool that is needed for distributing and storing container images. The tool has an open-source nature, so anyone can download and use it for setting up a container image registry.

When talking about more broader understanding, then it can relate to any service or tool that can host container images. Besides the Docker Registry, there is a diversity of other similar solutions such as:

• Google Cloud Container Registry.
• Harbor.
• JFrog Artifactory.
• Docker Hub.
• Azure Container Registry.

Advantages of using docker registry

The advantages of Docker Registry are the following:

• A centralized location for container images’ storage. Companies can easily track container images with this tool, so there is no need to manage images across various repositories.
• A centralized location for users to find container images. It doesn’t matter who the actual users are—external clients, employees, or even both—with Docker Registry, which is an easily accessible place where the images can be downloaded.
• Image versioning. One more huge advantage of the tool is the possibility of version specification. The image can be easily downloaded and run with any tool similar to Kubernetes or Docker. This is an extremely useful option when users need a specific version, so it is possible to offer alpha, beta, and even stable releases.
• Control of access. This is also a quite useful option where it is possible to allow some authenticated users access to specific images, while other images will be publicly accessible.
• Integration with Kubernetes and Docker. Easy integration with Docker and other tools is a huge benefit, so that it is possible to run images just by using one simple command. Such integration excludes the necessity to download the images and upload them to the needed environment. Most of the processes are automated once the container is run.

Docker Registry is not the only way through which it is possible to share and host container images. It is also possible to store a container image with the help of a network file share. However, this method is way more difficult for the users in terms of finding images. Also, it is impossible to request a certain version of the image.

Another popular option for hosting is through platforms such as GitHub, which also has lots of features. However, the issue is that such platforms are oriented towards source code hosting, not container images, so there is less integration with Docker.

That means Docker Registry is the only beneficial option that doesn’t have sharing and managing limitations like other tools.

Docker registry: how it functions

To understand how Docker registry functions, let’s first understand that there are 2 major groups of users.

The first main group of users is related to the developers who are creating containerized apps and want to share the image. In such a situation, Docker Registry is deployed as a container image. After that, the repositories are created. Once that is done, developers should specify access policies for the specific image.

The next group of users is those who just use the application. These users are using Docker Registry for searching container images and downloading them. In such a situation, Docker is configured for integration with the registry.

Steps to work with docker registry

To get a better understanding of how Docker Registry functions, let’s discuss a couple of the standard examples of how it is used via the command line.

For the downloading of the image, use the following command for Alpine Linux:

docker pull alpine:3.18

You can use this command by just specifying Alpine, or as in the above example, by adding the image version. This command will only download an image, but won’t start it.

To start and download a container with one command, use:

docker run alpine echo "Hello from Alpine"

For adding a container image to the registry, you will need to tag the image with the port of the Docker registry and the network address as follows:

docker image tag custom-app:v2 registry.example.org:5000/team/custom-app:v2

To add the image to the registry, use:

docker image push registry.example.org:5000/team/custom-app:v2

Setting up your own Docker registry server

To start a registry on the server with the Registry tool, you will need the following command:

docker run -d -p 8080:5000 --name private-registry registry:2

This command is extremely helpful for testing Docker Registry and quick deployment within the local development environment. It pulls the image and opens the source Docker Registry.

For persistent hosting, it is necessary to create a Service and a Pod in the following way:

 apiVersion: v1
kind: Pod
metadata:
  name: my-docker-registry-pod
  labels:
​app: registry
spec:
  containers:
​- name: registry
  ​image: registry:2.8.1
  ​ports:
    ​- containerPort: 5000
 
---
apiVersion: v1
kind: Service
metadata:
  name: docker-registry
spec:
  selector:
​app: registry
  ports:
​- port: 1234
  ​targetPort: 5000

Ensuring security in docker registry

Most Docker registry solutions are considered to be secure according to the default characteristics, but some other steps can improve the security level even more:

• Access control should be given to the specific users to minimize undesirable access by the general public.
• To exclude some vulnerabilities, you can run the registry on an unusual port. That is specifically crucial for the private images.
• To minimize other security risks, it is important to place the registry behind the firewall.
• Also, don’t forget to update registry software regularly to exclude other risks.
• Delete unnecessary images from the registry so it will be easier to track everything.

Top best practices for docker registry

Besides the security practices, some other helpful recommendations can get the most out of the Docker registry. Here are some of them:

• Choose the necessary type of registry for your specific situation. There are local registries, on-premises, and hosted ones.
• Use logs. To get a more secure environment, it is crucial to use auditing and logging features, which are usually provided by major Docker registries.
• Specify the image tags. When you are working with images, it is crucial to specify the image that you are planning to work on, otherwise, you will get the most recent version.
• Store only Docker images. In the registries, you can store any kind of information, but it is not the best possible practice. For other non-containerized apps, use specific hosting solutions.
• Minimize the size of the image. The bigger the size of the images is, the more time it will take to download, and it will use more bandwidth.