Jon Langemak of Das Blinken Lichten comments:

So we’ve had some time to digest what containers and images are.   Now let’s talk in a little greater detail about images and how they layer.   A key piece of docker is how the images stack.   For instance, let’s quickly build a container that has 3 user image layers in it.   Recall, images are the read-only pieces of the container so having 3 user layers implies that I have done 3 commits and any changes after that will be in the 4th read/write layer that lives in the container itself…

More great Docker writing from Jon. Read up on this, as it appears that you’ll be using very shortly.

Read more at: Docker essentials — More work with images