Is Docker a VM? Docker isn’t a virtual machine – it is a configuration management tool. You can find some interesting facts about containers implementation and isolation at doger.io. let’s not forget that Docker for Mac and Docker for Windows do use the virtualization layer.
Why Docker is so fast? Since the host kernel is shared amongst Docker containers, applications only ship with what they need to run—no more, no less. This makes Docker applications easier and more lightweight to deploy and faster to start up than virtual machines.
Why do we need Docker? Docker streamlines the development lifecycle by allowing developers to work in standardized environments using local containers which provide your applications and services. Containers are great for continuous integration and continuous delivery (CI/CD) workflows.
Do containers have an OS? Yes, they do. Every container is based on an OS image, e.g. Alpine, CentOS or Ubuntu. They just share the host kernel, but run every user-space process in a separate name space specific for that container.