CoreOS is a new Linux distribution that has been re-architected to provide features needed to run modern infrastructure stacks. The strategies and architectures that influence CoreOS allow companies like Google, Facebook and Twitter to run their services at scale with high resilience.
By default CoreOS is pre-configured with tools to run Linux containers and be distributed. A key feature is that the container runtime (e.g. Docker) is automatically configured on each CoreOS machine. Also CoreOS provides automatic OS updates which means you get all Updates per default and you don’t have to worry about old versions.
On CoreOS you can use docker with fleet. Fleet is a distributed init system which presents your entire cluster as a single init system. You are able to start fleet units by using extended systemd unit files. With fleet you are able to run distributed containerized apps.
A major benefit of running CoreOS is etcd. etcd is a distributed key value store which is used by many projects like Kubernetes, Cloud Foundry and many more. You can use etcd for simple service discovery and much more. Also major cloud providers offer CoreOS support.