Another central piece in the CoreOS ecosystem worth mentioning is their open-source etcd project. etcd is a distributed and consistent key-value store. A RESTful API is used to interface with etcd, so it's easy to integrate with your project.

If it sounds familiar, it's because we saw this process running in Chapter 1, Introduction to Kubernetes, in the Services running on the master section. Kubernetes actually utilizes etcd to keep track of cluster configuration and current state. K8s uses it for the service discovery capabilities as well. For more details, refer to https://github.com/coreos/etcd.