Add kube-apiserver, kube-controller-manager, kube-scheduler and etcd to glossary. (#6600)

* Move master component definitions to glossary

* review comments

* Update controller.yaml

Making a trivial change to un-stuck Travis

* Update controller.yaml

Removing trivial change

_data/glossary/controller.yaml

@@ -0,0 +1,12 @@
+id: controller
+name: Controller
+full-link: /docs/admin/kube-controller-manager/
+related:
+- controller-manager
+tags:
+- architecture
+- fundamental
+short-description: >
+  A control loop that watches the shared state of the cluster through the {% glossary_tooltip text="apiserver" term_id="kube-apiserver" %} and makes changes attempting to move the current state towards the desired state.
+long-description: >
+  Examples of controllers that ship with Kubernetes today are the replication controller, endpoints controller, namespace controller, and serviceaccounts controller.

_data/glossary/etcd.yaml

@@ -0,0 +1,11 @@
+id: etcd
+name: etcd
+full-link: /docs/tasks/administer-cluster/configure-upgrade-etcd/
+tags:
+- architecture
+- storage
+short-description: >
+  Consistent and highly-available key value store used as Kubernetes' backing store for all cluster data.
+long-description: >
+  Always have a backup plan for etcd's data for your Kubernetes cluster.
+  For in-depth information on etcd, see [etcd documentation](https://github.com/coreos/etcd/blob/master/Documentation/docs.md).

_data/glossary/kube-apiserver.yaml

@@ -0,0 +1,12 @@
+id: kube-apiserver
+name: kube-apiserver
+full-link: /docs/reference/generated/kube-apiserver/
+aka:
+- apiserver
+tags:
+- architecture
+- fundamental
+short-description: >
+  Component on the master that exposes the Kubernetes API. It is the front-end for the Kubernetes control plane. 
+long-description: >
+  It is designed to scale horizontally -- that is, it scales by deploying more instances. See [Building High-Availability Clusters](/docs/admin/high-availability/).

_data/glossary/kube-controller-manager.yaml

@@ -0,0 +1,14 @@
+id: kube-controller-manager
+name: kube-controller-manager
+full-link: /docs/reference/generated/kube-controller-manager/
+aka:
+- controller-manager
+related:
+- controller
+tags:
+- architecture
+- fundamental
+short-description: >
+  Component on the master that runs {% glossary_tooltip text="controllers" term_id="controller" %}.
+long-description: >
+  Logically, each {% glossary_tooltip text="controller" term_id="controller" %} is a separate process, but to reduce complexity, they are all compiled into a single binary and run in a single process.

_data/glossary/kube-scheduler.yaml

@@ -0,0 +1,13 @@
+id: kube-scheduler
+name: kube-scheduler
+full-link: /docs/reference/generated/kube-scheduler/
+aka:
+- scheduler
+tags:
+- architecture
+short-description: >
+  Component on the master that watches newly created pods that have no node assigned, and selects a node for them to run on.
+long-description: >
+  Factors taken into account for scheduling decisions include individual and collective resource requirements, 
+  hardware/software/policy constraints, affinity and anti-affinity specifications, data locality, inter-workload interference
+  and deadlines.