Learn Docker - Fundamentals of Docker 18.x

The writable container layer

As we have discussed, a container image is made of a stack of immutable or read-only layers. When the Docker engine creates a container from such an image, it adds a writable container layer on top of this stack of immutable layers. Our stack now looks as follows:

The writable container layer

The container layer is marked as read/write. Another advantage of the immutability of image layers is that they can be shared among many containers created from this image. All that is needed is a thin, writable container layer for each container:

Multiple containers sharing the same image layers

This technique, of course, ...