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CoreOS is an important part of many container stacks. In this series of posts, we’re going to take a look at CoreOS, why it’s important, and how it works. If you don’t know anything about CoreOS already, don’t worry. We start at the beginning.
The Basics and How CoreOS Is Different From Other Linux Systems
CoreOS is designed for security, consistency, and reliability.
Automatic CoreOS updates are done using an active/passive dual-partition scheme to update CoreOS as a single unit, instead of using a package-by-package method. We go over this in detail later.
Instead of installing packages via yum or APT, CoreOS uses Linux containers to manage your services at a higher level of abstraction. A single service's code and all dependencies are packaged within a container that can be run on a single CoreOS machine or many CoreOS machines in a cluster.
Linux containers provide similar benefits to complete virtual machines, but are focused on applications instead of entire virtualized hosts. Because containers don’t run their own Linux kernel or require a hypervisor, they have almost no performance overhead. The lack of overhead allows you to gain density which means fewer machines to operate and a lower compute spend.