tl;dr the author uses "docker export" to squash a container image layers into a rootfs, and uses chroot to make it the root of that filesystem and runs a binary

tl;dr the author uses "docker export" to squash a container image layers into a rootfs, and uses chroot to make it the root of that filesystem and runs a binary there. This practically has nothing to do with the term "containers". Author says "Others will tell you containers are about namespaces [...] But for me, containers are just chrooted processes. " , however containers are very much about isolation, resource controls, and various network features like port mappings for many people. So you really didn't build anything even remotely resembling a container runtime, you redefined the term and built something that does "docker export | tar zxvf && cd /dir && chroot /dir && /prog". :)