Merge pull request #6919 from k8s-infra-cherrypick-robot/cherry-pick-…

…6845-to-release-1.2

[release-1.2] 📖 Add Clusterclass and RuntimeSDK terms to glossary

docs/book/src/reference/glossary.md

@@ -1,6 +1,6 @@
 # Table of Contents
 
-[A](#a) | [B](#b) | [C](#c) | [D](#d) | [H](#h) | [I](#i) | [K](#k) | [M](#m) | [N](#n) | [O](#o) | [P](#p) | [S](#s) | [T](#t) | [W](#w)
+[A](#a) | [B](#b) | [C](#c) | [D](#d) | [E](#e) | [H](#h) | [I](#i) | [K](#k) | [L](#l)| [M](#m) | [N](#n) | [O](#o) | [P](#p) | [R](#r) | [S](#s) | [T](#t) | [W](#w)
 
 # A
 ---
@@ -84,12 +84,21 @@ Cluster API Provider Azure
 
 A full Kubernetes deployment. See Management Cluster and Workload Cluster.
 
+### ClusterClass
+
+A collection of templates that define a topology (control plane and workers) to be used to continuously reconcile one or more Clusters.
+See [ClusterClass](../tasks/experimental-features/cluster-class/index.md)
+
 ### Cluster API
 
 Or __Cluster API project__
 
 The Cluster API sub-project of the SIG-cluster-lifecycle. It is also used to refer to the software components, APIs, and community that produce them.
 
+### Cluster API Runtime
+
+The Cluster API execution model, a set of controllers cooperating in managing the Kubernetes cluster lifecycle.
+
 ### Control plane
 
 The set of Kubernetes services that form the basis of a cluster. See also [https://kubernetes.io/docs/concepts/#kubernetes-control-plane](https://kubernetes.io/docs/concepts/#kubernetes-control-plane) There are two variants:
@@ -104,6 +113,19 @@ The set of Kubernetes services that form the basis of a cluster. See also [https
 
 A feature implementation offered as part of the Cluster API project, infrastructure providers can swap it out for a different one.
 
+# E
+---
+
+### External patch
+
+[Patch](#patch) generated by an external component using [Runtime SDK](#runtime-sdk). Alternative to [inline patch](#inline-patch).
+
+### External patch extension
+
+A [runtime extension] that implements a [topology mutation hook]
+
+See [Runtime Extension](#runtime-extension), [topology mutation hook](#topology-mutation-hook)
+
 # H
 ---
 
@@ -122,6 +144,10 @@ see [Server](#server)
 
 A source of computational resources (e.g. machines, networking, etc.). Examples for cloud include AWS, Azure, Google, etc.; for bare metal include VMware, MAAS, metal3.io, etc. When there is more than one way to obtain resources from the same infrastructure provider (e.g. EC2 vs. EKS) each way is referred to as a variant.
 
+### Inline patch 
+
+A [patch](#patch) defined inline in a [ClusterClass](#clusterclass). An alternative to an [external patch](#external-patch).
+
 ### Instance
 
 see [Server](#server)
@@ -143,6 +169,13 @@ A cluster that passes the Kubernetes conformance tests.
 
 Refers to the [main Kubernetes git repository](https://github.com/kubernetes/kubernetes) or the main Kubernetes project.
 
+# L
+---
+
+### Lifecycle hook
+A [Runtime Hook](#runtime-hook) that allows external components to interact with the lifecycle of a Cluster.
+
+See [Implementing Lifecycle Hooks](../tasks/experimental-features/runtime-sdk/implement-lifecycle-hooks.md)
 # M
 ---
 
@@ -191,6 +224,10 @@ A generically understood combination of a kernel and system-level userspace inte
 # P
 ---
 
+### Patch 
+
+A set of instructions describing modifications to a Kubernetes object. Examples include JSON Patch and JSON Merge Patch.
+
 ### Pivot
 
 Pivot is a process for moving the provider components and declared cluster-api resources from a Source Management cluster to a Target Management cluster.
@@ -210,6 +247,27 @@ it usually contains Custom Resource Definitions (CRDs), Deployments (to run the
 
 Existing Cluster API implementations consist of generic and infrastructure provider-specific logic. The [infrastructure provider](#infrastructure-provider)-specific logic is currently maintained in infrastructure provider repositories.
 
+# R
+---
+
+### Runtime Extension
+
+An external component which is part of a system built on top of Cluster API that can handle requests for a specific Runtime Hook.
+
+See [Runtime SDK](#runtime-sdk)
+
+### Runtime Hook
+
+A single, well identified, extension point allowing applications built on top of Cluster API to hook into specific moments of the [Cluster API Runtime](#cluster-api-runtime), e.g. [BeforeClusterUpgrade](../tasks/experimental-features/runtime-sdk/implement-lifecycle-hooks.md#beforeclusterupgrade), [TopologyMutationHook](#topology-mutation-hook).
+
+See [Runtime SDK](#runtime-sdk)
+
+### Runtime SDK
+
+A developer toolkit required to build Runtime Hooks and Runtime Extensions.
+
+See [Runtime SDK](../tasks/experimental-features/runtime-sdk/index.md)
+
 # S
 ---
 
@@ -226,9 +284,31 @@ is running as a static pod.
 
 The infrastructure that backs a [Machine Resource](#machine), typically either a cloud instance, virtual machine, or physical host.
 
+# T
+---
+
+### Topology
+
+A field in the Cluster object spec that allows defining and managing the shape of the Cluster's control plane and worker machines from a single point of control. The Cluster's topology is based on a [ClusterClass](#clusterclass).
+
+See [ClusterClass](#clusterclass)
+
+
+### Topology Mutation Hook
+
+A [Runtime Hook](#runtime-hook) that allows external components to generate [patches](#patch) for customizing Kubernetes objects that are part of a [Cluster topology](#topology).
+
+See [Topology Mutation](../tasks/experimental-features/runtime-sdk/implement-topology-mutation-hook.md)
+
 # W
 ---
 
 ### Workload Cluster
 
 A cluster created by a ClusterAPI controller, which is *not* a bootstrap cluster, and is meant to be used by end-users, as opposed to by CAPI tooling.
+
+### WorkerClass
+
+A collection of templates that define a set of worker nodes in the cluster. A ClusterClass contains zero or more WorkerClass definitions.
+
+See [ClusterClass](#clusterclass)