The interface layer is made up of commonly used tools, systems, user interfaces, and libraries that other custom Kubernetes distributions might use. The kubectl library is a great example of the interface layer, and importantly it's not seen as a privileged part of the Kubernetes system; it's considered a client tool in order to provide maximum flexibility for the Kubernetes API. If you run $ kubectl -h, you will get a clear picture of the functionality exposed to the interface layer.

Other pieces at this layer include cluster federation tools, dashboards, Helm, and client libraries such as client-node, KubernetesClient, and python. These tools provide common tasks for you, so you don't have to worry about writing code for authentication, for example. These libraries use the Kubernetes Service Account to authenticate to the cluster.