Correct, docker is not an implementation of linux containers. The heavy lifting is done by lxc (and alternatives like openvz). What docker brings is a way for

Correct, docker is not an implementation of linux containers. The heavy lifting is done by lxc (and alternatives like openvz). What docker brings is a way for backend developers to package and distribute their app into portable, sandboxed containers (think "iphone apps for the server"). This is only possible now that linux has decent container support, because it means the vast majority of servers out there can potentially run a docker container unmodified.