What is a container? Search the web, and the answers typically fall under two categories.

First, that containers are like virtual machines. This is a terrible analogy; containers are entirely unlike virtual machines. It doesn't further anyone's understanding of containers, and if I had one wish, it would be that people would stop saying this!

Second, a discussion of namespaces and control groups. This covers process isolation and is important for understanding container security and interaction with host resources. While this is relevant to the runtime engine responsible for running a container, it's often beyond the reach of the end user, nor does it impact most of their day-to-day interactions with containers, including building and running container images.

A third, overlooked element really makes containers tick: Union Filesystems. These are the magic behind the speed, efficiency, and capacity containers deliver. Understanding how union filesystems work is critical to building optimized images and achieving efficient container deployments. In this session, we'll demonstrate what happens on the host filesystem when running a container and how to leverage that knowledge to plan and build more efficient container images. You'll also discover the purpose and benefit of volumes and how they're integral to maximizing capacity and maintaining performance in container environments. Finally, you'll learn a better answer to the question, "What is a container?"