As we have seen, Docker helps us to reproduce the setup used to deploy an application, but it also helps us to distribute the application to be used in different environments. This task can be performed using registries.

A registry is a service that is responsible for hosting and distributing Docker images. The default registry used by Docker is Docker Hub. There are other options available on the market that can be used as Docker registries, including the following:

• Quay
• Google Container Registry
• AWS Container Registry

Docker Hub is really popular because it works in ways that you do not even notice. For instance, if you're creating a container and the image doesn't exist in your local repository, it will automatically download the image from Docker Hub. All the existing images are created by someone else and published in these registries. In the same way, we can publish our own images in order to make them available to other people within an organization by using private repositories. Alternatively, you can publish them in public repositories. You can also self-host a Docker registry on your own hardware using solutions such as Nexus, JFrog, and so on.

Docker Hub has a free plan that allows you to create an unlimited number of public repositories and one private repository. It also offers another plan that enables you to have more private repositories, if necessary. We use Docker Hub for Docker in the same way that we use GitHub for Git repositories.