The discovery service and global configuration store and scheduler are implemented with the etcd and kube-scheduler master components:

• etcd is a consistent and highly-available key-value (KV) store used as both the Discovery Service and Global Configuration Store.

  Because the discovery service and global configuration store both hold information about the services, and each are accessible by all nodes, etcd can serve both purposes. Whenever a service registers itself with the discovery service, it will also be returned a set of configuration settings.

• kube-scheduler is a scheduler. It keeps track of which applications are unassigned to a node (and thus not running) and makes the decision as to which node to assign it to.

In addition to these essential cluster management components, Kubernetes also provides additional Master Components to make working with Kubernetes easier.

By default, all Master Components run on a single Master Node, which runs only the Master Components and not other containers/services. However, they can be configured to be replicated in order to provide redundancy.