Shipping applications is an integral part of the Docker platform. The Docker Engine can download images from a central location to run containers from them, and can also upload images which were built locally to a central location. These shared image stores are called registries, and in this chapter we'll look more closely at how image registries work and the types of registries that are available to you.

The primary image registry is Docker Hub, which is a free online service and is the default location for the Docker service to work with images. Docker Hub is a great place for the community to share images which are built to package open source software and are free to redistribute. Docker Hub has been hugely successful. At the time of writing this book, there are hundreds of thousands of images available on it, with billions of downloads every year.

A public registry may not be suitable for your own applications. Docker Hub also offers a commercial plan so that you can host private images (in a similar way to how GitHub lets you host public and private source code repositories), and there are other commercial registries that add features like security scanning. You can also run your own registry server in your environment by using an open source registry implementation which is freely available.

In this chapter I'll show you how to use those registries, and I'll cover the finer details of tagging images – which is how you can version your Docker images – and working with images from different registries. We'll cover:

• Understanding registries and repositories
• Running a local image registry
• Pushing and pulling images with a local registry
• Using a commercial registry