Container images are templates from which containers are created. These images are not made up of just one monolithic block but are composed of many layers. The first layer in the image is also called the base layer. We can see this in the following graphic:
The image as a stack of layers
Each individual layer contains files and folders. Each layer only contains the changes to the filesystem with respect to the underlying layers. Docker uses a Union filesystem—as discussed in Chapter 3, Mastering Containers — to create a virtual filesystem out of the set of layers. A storage driver handles the details regarding the way ...
