CoreOS from scratch - Part 1: OS installation

In the "CoreOS from scratch" series I'll try to explain how to install CoreOS three node cluster on VirtualBox using manual process. I believe that understanding installation "the hard way" leads to better understanding of whats going on by using CoreOS with Vagrant as well as helps you to install CoreOS on bare metal.

But first really very fast description of what CoreOS is.

CoreOS is just like any other Linux Distro based on Gentoo.

Gentoo wiki states:

CoreOS is a new Linux distribution that has been rearchitected to provide features needed to run modern infrastructure stacks.

I think this describes CoreOS quite well. CoreOS is Linux operating system that is specially made to run containers (containerized applications) like Docker or Rocket. Meaning it is not operating system you would like to use for desktop, or as typical Linux server where you install any software your corporate IT environment needs. Besides running containerized applications CoreOS comes with full stack of tools needed to form and operate clusters.