Docker is a lightweight alternative to virtual machines like VirtualBox. It uses linux containers (lxc) and cgroups to separate vm instances (called containers in docker). That is a recent Linux features which makes kernel 3.8 a minimum requirement. Containers have their own file system, network interfaces, processes. You can expose container ports outside of container and link containers together. Images in docker can be build from other images, and containers is a snapshots of the image....