In the naughts, virtualization developed as a software layer to abstract physical hardware and provide so-called "virtual machines" that, instead of working exc

In the naughts, virtualization developed as a software layer to abstract physical hardware and provide so-called "virtual machines" that, instead of working exclusively with hardware, function as a group and share resources as a pool. Docker provides one more layer of abstraction and grouping where a machine (or, commonly, a virtual machine) abstracts its resources in order to provide them to thread-like "containers." These containers share their resources with other containers running on a given host. A docker container, written like a spec into a `Dockerfile`, is a way to package your application as if there was a `run.sh` that would install your OS, any dependencies and your application itself -- and, importantly, run that application after everything is installed. The host can choose to surface to the world any ports on the running container, or keep them private to itself. The container draws from the host's pool of resources so long as your application continues to run inside the "thread" managed by docker.