Improve provider definition in docs

Author: fabriziopandini

docs/book/src/reference/glossary.md

@@ -23,6 +23,13 @@ The process of turning a server into a Kubernetes node. This may involve assembl
 
 A temporary cluster that is used to provision a Target Management cluster.
 
+### Bootstrap provider
+
+Refers to a [provider](#provider) that implements a solution for the [bootstrap](#bootstrap) process.
+Bootstrap provider's interaction with Cluster API is based on what is defined in the [Cluster API contract](#contract). 
+
+See [CABPK](#CABPK). 
+
 # C
 ---
 
@@ -83,6 +90,12 @@ Cluster API Provider VMware Cloud Director
 ### CAPZ
 Cluster API Provider Azure
 
+### Cloud provider
+
+Or __Cloud service provider__
+
+Refers to an information technology (IT) company that provides computing resources (e.g. AWS, Azure, Google, etc.).
+
 ### Cluster
 
 A full Kubernetes deployment. See Management Cluster and Workload Cluster.
@@ -98,23 +111,48 @@ 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.
 
+See [core provider](#core-provider)
+
 ### Cluster API Runtime
 
 The Cluster API execution model, a set of controllers cooperating in managing the Kubernetes cluster lifecycle.
 
+### Contract
+
+Or __Cluster API contract__
+
+Defines a set of rules a [provider](#provider) is expected to comply with in order to interact with Cluster API.
+Those rules can be in the form of CustomResourceDefinition (CRD) fields and/or expected behaviors to be implemented.
+
 ### 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:
 
 * __Self-provisioned__: A Kubernetes control plane consisting of pods or machines wholly managed by a single Cluster API deployment.
-* __External__: A control plane offered and controlled by some system other than Cluster API (e.g., GKE, AKS, EKS, IKS).
+* __External__ or __Managed__: A control plane offered and controlled by some system other than Cluster API (e.g., GKE, AKS, EKS, IKS).
+
+### Control plane provider
+
+Refers to a [provider](#provider) that implements a solution for the management of a Kubernetes [control plane][#control-plane].
+Control plane provider's interaction with Cluster API is based on what is defined in the [Cluster API contract](#contract).
+
+See [KCP](#KCP).
+
+### Core provider
+
+Refers to a [provider](#provider) that implements Cluster API core controllers; if you 
+consider that the first project that must be deployed in a management Cluster is Cluster API itself, it should be clear why
+the Cluster API project is also referred to as the core provider.
+
+See [CAPI](#cluster-api).
 
 # D
 ---
 
 ### Default implementation
 
-A feature implementation offered as part of the Cluster API project, infrastructure providers can swap it out for a different one.
+A feature implementation offered as part of the Cluster API project and maintained by the CAPI core team; For example
+[KCP](#KCP) is a default implementation for a [control plane provider](#control-plane-provider).
 
 # E
 ---
@@ -145,7 +183,15 @@ see [Server](#server)
 
 ### Infrastructure provider
 
-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.
+Refers to a [provider](#provider) that implements provisioning of infrastructure/computational resources required by 
+the Cluster or by Machines (e.g. VMs, networking, etc.).
+Infrastructure provider's interaction with Cluster API is based on what is defined in the [Cluster API contract](#contract).
+
+Clouds infrastructure providers include AWS, Azure, or Google; while VMware, MAAS, or metal3.io can be defined as bare metal providers.
+When there is more than one way to obtain resources from the same infrastructure provider (e.g. EC2 vs. EKS in AWS) each way is referred to as a variant.
+
+See e.g. [CAPA][#CAPA], [CAPC][#CAPC], [CAPD][#CAPD], [CAPG][#CAPG], [CAPH][#CAPH], [CAPIBM][#CAPIBM], [CAPN][#CAPN],
+[CAPX][#CAPX], [CAPK][#CAPK], [CAPO][#CAPO], [CAPOCI][#CAPOCI], [CAPV][#CAPV], [CAPVC][#CAPVC], [CAPVCD][#CAPVCD], [CAPZ][#CAPZ]
 
 ### Inline patch 
 
@@ -159,6 +205,11 @@ see [Server](#server)
 
 A resource that does not mutate.  In kubernetes we often state the instance of a running pod is immutable or does not change once it is run.  In order to make a change, a new pod is run.  In the context of [Cluster API](#cluster-api) we often refer to a running instance of a [Machine](#machine) as being immutable, from a [Cluster API](#cluster-api) perspective.
 
+### IPAM provider
+
+Refers to a [provider](#provider) that allows Cluster API to interact with IPAM solutions.
+IPAM provider's interaction with Cluster API is based on the `IPAddressClaim` and `IPAddress` API types.
+
 # K
 ---
 
@@ -243,16 +294,27 @@ The pivot process is also used for deleting a management cluster and could also
 
 ### Provider
 
-See [Infrastructure Provider](#infrastructure-provider)
+Or __Cluster API provider__
+
+This term was originally used as abbreviation for [Infrastructure provider](#infrastructure-provider), but currently it is used
+to refer to any project that can be deployed and provides functionality to the Cluster API management Cluster.
+
+See [Bootstrap provider](#bootstrap-provider), [Control plane provider](#control-plane-provider), [Core provider](#core-provider),
+[Infrastructure provider](#infrastructure-provider), [IPAM provider](#ipam-provider)  [Runtime extension provider](#runtime-extension-provider).
 
 ### Provider components
 
-Refers to the YAML artifact a provider publishes as part of their releases which is required to use the provider components,
-it usually contains Custom Resource Definitions (CRDs), Deployments (to run the controller manager), RBAC, etc.
+Refers to the YAML artifact published as part of the release process for [providers](#provider);
+it usually includes Custom Resource Definitions (CRDs), Deployments (to run the controller manager), RBAC, etc.
+
+In some cases, the same expression is used to refer to the instances of above components deployed in a management cluster.
 
-### Provider implementation
+See [Provider repository](#provider-repository)
 
-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.
+### Provider repository
+
+Refers to the location where the YAML for [provider components](#provider-components) are hosted; usually a provider repository hosts
+many version of provider components, one for each released version.
 
 # R
 ---
@@ -263,6 +325,11 @@ An external component which is part of a system built on top of Cluster API that
 
 See [Runtime SDK](#runtime-sdk)
 
+### Runtime Extension provider
+
+Refers to a [provider](#provider) that implements one or more [runtime extensions](#runtime-extension).
+Runtime Extension provider's interaction with Cluster API are based on the Open API spec for [runtime hooks](#runtime-hook).
+
 ### 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).

docs/book/src/user/concepts.md

@@ -4,21 +4,22 @@
 
 ## Management cluster
 
-A Kubernetes cluster that manages the lifecycle of Workload Clusters. A Management Cluster is also where one or more Infrastructure Providers run, and where resources such as Machines are stored.
+A Kubernetes cluster that manages the lifecycle of Workload Clusters. A Management Cluster is also where one or more providers run, and where resources such as Machines are stored.
 
 ### Workload cluster
 
 A Kubernetes cluster whose lifecycle is managed by a Management Cluster.
 
 ## Infrastructure provider
 
-A source of computational resources, such as compute and networking. For example, cloud Infrastructure Providers include AWS, Azure, and Google, and bare metal Infrastructure Providers include VMware, MAAS, and metal3.io.
+A component responsible for the provisioning of infrastructure/computational resources required by the Cluster or by Machines (e.g. VMs, networking, etc.). 
+For example, cloud Infrastructure Providers include AWS, Azure, and Google, and bare metal Infrastructure Providers include VMware, MAAS, and metal3.io.
 
 When there is more than one way to obtain resources from the same Infrastructure Provider (such as AWS offering both EC2 and EKS), each way is referred to as a variant.
 
 ## Bootstrap provider
 
-The Bootstrap Provider is responsible for:
+A component responsible for turning a server into a Kubernetes node as well as for:
 
 1. Generating the cluster certificates, if not otherwise specified
 1. Initializing the control plane, and gating the creation of other nodes until it is complete
@@ -28,11 +29,13 @@ The Bootstrap Provider is responsible for:
 
 The [control plane](https://kubernetes.io/docs/concepts/overview/components/) is a set of components that serve the Kubernetes API and continuously reconcile desired state using [control loops](https://kubernetes.io/docs/concepts/architecture/controller/).
 
-* __Machine-based__ control planes are the most common type. Dedicated machines are provisioned, running [static pods](https://kubernetes.io/docs/tasks/configure-pod-container/static-pod/) for components such as [kube-apiserver](https://kubernetes.io/docs/admin/kube-apiserver/), [kube-controller-manager](https://kubernetes.io/docs/admin/kube-controller-manager/) and [kube-scheduler](https://kubernetes.io/docs/admin/kube-scheduler/).
+* __Self-provisioned__: A Kubernetes control plane consisting of pods or machines wholly managed by a single Cluster API deployment.
+  e.g kubeadm uses [static pods](https://kubernetes.io/docs/tasks/configure-pod-container/static-pod/) for running components such as [kube-apiserver](https://kubernetes.io/docs/admin/kube-apiserver/), [kube-controller-manager](https://kubernetes.io/docs/admin/kube-controller-manager/) and [kube-scheduler](https://kubernetes.io/docs/admin/kube-scheduler/)
+  on control plane machines.
 
 * __Pod-based__ deployments require an external hosting cluster. The control plane components are deployed using standard *Deployment* and *StatefulSet* objects and the API is exposed using a *Service*.
 
-* __External__ control planes are offered and controlled by some system other than Cluster API, such as GKE, AKS, EKS, or IKS.
+* __External__  or __Managed__ control planes are offered and controlled by some system other than Cluster API, such as GKE, AKS, EKS, or IKS.
 
 The default provider uses kubeadm to bootstrap the control plane. As of v1alpha3, it exposes the configuration via the `KubeadmControlPlane` object. The controller, `capi-kubeadm-control-plane-controller-manager`, can then create Machine and BootstrapConfig objects based on the requested replicas in the `KubeadmControlPlane` object.
 

docs/proposals/20220221-runtime-SDK.md

@@ -69,6 +69,8 @@ Refer to the [Cluster API Book Glossary](https://cluster-api.sigs.k8s.io/referen
   into specific moments of the workload cluster’s lifecycle, e.g. `BeforeClusterUpgrade`, `BeforeMachineRemediation`.
 - **Runtime Extension**: an external component which is part of a system/product built on top of Cluster API that can
   handle requests for a specific Runtime Hook.
+- **Runtime Extension Provider**: a project that provides a runtime extension and the yaml for installing it as part of 
+  its release artefacts.
 
 ## Summary
 
@@ -145,6 +147,7 @@ To define the Runtime SDK and more specifically
 - Improve the Runtime Extension developer guide based on experience and feedback;
 - Add metrics about Runtime Extension calls (usage, usage vs deprecated versions, duration, error rate etc.);
 - Allow providers to use the same SDK to define their own hooks.
+- Improve clusterctl to deploy and manage runtime extension providers
 
 ## Proposal