Docker Layers and Caching

A registry is a way to store and distribute your Docker images. When you pull a Docker image from a registry, you might have noticed that the image is pulled in pieces and not as a single image. The same thing happens when you build an image on your system.

This is because Docker images consist of layers. When you create a new image using a Dockerfile, it will create more layers on top of the existing image you've built from. Each command you specify in the Dockerfile will create a new layer, with each containing all of the filesystem changes that occur before the command was performed and then after. When you run the image as a container from a Dockerfile, you're creating readable and writable layers on top of an existing group of read-only layers. This writable layer is known as the container layer.

As you'll see in the following exercises, when you build a container from a Dockerfile, the output presented shows each command run in...