DevOps Articles

Desacralizing the Linux overlay filesystem in Docker

Overlay filesystems (also called union filesystems) is a fundamental technology in Docker to create images and containers. Multiple filesystems, which are just directories, are superposed one on top of another to create a new filesystem.

We will learn how to create an overlay filesystem ourselves and how Docker is using it to build images and run containers.

Docker uses the overlay filesystem to create images as well as to position the container layer on top of the image layers.

Once we understand how overlay filesystems work, it is quite easy to see how Docker used the overlay filesystem in its Dockerfile with additional caching between each layer.