Docker Tutorial for Free

Docker is a software technology providing containers, promoted by the company Docker, Inc.Docker provides an additional layer of abstraction and automation of operating-system-level virtualization on Windows and Linux.

Docker uses the resource isolation features of the Linux kernel such as cgroups and kernel namespaces, and a union-capable file system such as OverlayFS and others[to allow independent "containers" to run within a single Linux instance, avoiding the overhead of starting and maintaining virtual machines