docs: move clusterctl to book

Author: kikisdeliveryservice

docs/book/src/tooling/clusterctl.md

@@ -1 +1,94 @@
-# Clusterctl
+# Using `clusterctl` to create a cluster from scratch
+<!-- START doctoc generated TOC please keep comment here to allow auto update -->
+<!-- DON'T EDIT THIS SECTION, INSTEAD RE-RUN doctoc TO UPDATE -->
+
+
+- [What is `clusterctl`?](#what-is-clusterctl)
+- [Creating a cluster](#creating-a-cluster)
+  - [Creating a workload cluster using the management cluster](#creating-a-workload-cluster-using-the-management-cluster)
+
+<!-- END doctoc generated TOC please keep comment here to allow auto update -->
+
+This document provides an overview of how `clusterctl` works and explains how one can use `clusterctl`
+to create a Kubernetes cluster from scratch.
+
+## What is `clusterctl`?
+
+`clusterctl` is a CLI tool to create a Kubernetes cluster. `clusterctl` is provided by the [provider implementations](https://cluster-api.sigs.k8s.io/reference/providers).
+It uses Cluster API provider implementations to provision resources needed by the Kubernetes cluster.
+
+## Creating a cluster
+
+`clusterctl` needs 4 YAML files to start with: `provider-components.yaml`, `cluster.yaml`, `machines.yaml` ,
+`addons.yaml`.
+
+* `provider-components.yaml` contains the *Custom Resource Definitions ([CRDs](https://Kubernetes.io/docs/concepts/extend-Kubernetes/api-extension/custom-resources/))* 
+of all the resources that are managed by Cluster API. Some examples of these resources
+are: `Cluster`, `Machine`, `MachineSet`, etc. For more details about Cluster API resources
+click [here](https://cluster-api.sigs.k8s.io/architecture/controllers).
+* `cluster.yaml` defines an object of the resource type `Cluster`.
+* `machines.yaml` defines an object of the resource type `Machine`. Generally creates the machine
+that becomes the control-plane.
+* `addons.yaml` contains the addons for the provider.
+
+Many providers implementations come with helpful scripts to generate these YAMLS. Provider implementation
+can be found [here](https://cluster-api.sigs.k8s.io/reference/providers).  
+
+`clusterctl` also comes with additional features. For example, `clusterctl` can also take in an optional
+`bootstrap-only-components.yaml` to provide resources to the bootstrap cluster without also providing them
+to the target cluster post-pivot.
+
+For more details about all the supported options run:
+
+```
+clusterctl create cluster --help
+```
+
+After generating the YAML files run the following command:
+
+```
+clusterctl create cluster --provider <PROVIDER> --bootstrap-type <BOOTSTRAP CLUSTER TYPE> -c cluster.yaml -m machines.yaml -p provider-components.yaml --addon-components addons.yaml
+```
+
+Example usage:
+
+```
+# VMware vSphere
+clusterctl create cluster --provider vsphere --bootstrap-type kind -c cluster.yaml -m machines.yaml -p provider-components.yaml --addon-components addons.yaml
+
+# Amazon AWS
+clusterctl create cluster --provider aws --bootstrap-type kind -c cluster.yaml -m machines.yaml -p provider-components.yaml --addon-components addons.yaml
+```
+
+**What happens when we run the command?**  
+After running the command first it creates a local cluster. If `kind` was passed as the `--bootstrap-type`
+it creates a local [kind](https://kind.sigs.k8s.io/) cluster. This cluster is generally referred to as the *bootstrap cluster*.  
+On this kind Kubernetes cluster the `provider-components.yaml` file is applied. This step loads the CRDs into
+the cluster. It also creates 2 [StatefulSet](https://Kubernetes.io/docs/concepts/workloads/controllers/statefulset/)
+pods that run the cluster api controller and the provider specific controller. These pods register the custom
+controllers that manage the newly defined resources (`Cluster`, `Machine`, `MachineSet`, etc).  
+
+Next, `clusterctl` applies the `cluster.yaml` and `machines.yaml` to the local kind Kubernetes cluster. This
+step creates a Kubernetes cluster with only a control-plane(as defined in `machines.yaml`) on the specified
+provider. This newly created cluster is generally referred to as the *management cluster* or *pivot cluster*
+or *initial target cluster*. The management cluster is responsible for creating and maintaining the work-load cluster.  
+  
+Lastly, `clusterctl` moves all the CRDs and the custom controllers from the bootstrap cluster to the
+management cluster and deletes the locally created bootstrap cluster. This step is referred to as the *pivot*.
+
+### Creating a workload cluster using the management cluster
+
+The *workload cluster* also sometimes referred to as the *target cluster* is the Kubernetes cluster on to which
+the final application is deployed. The target cluster is responsible for handling the workload of the application,
+not the management cluster.
+
+As the management cluster is up we can create a workload cluster by simply applying the appropriate
+`cluster.yaml`, `machines.yaml` and `machineset.yaml` on the management cluster. This will create the VMs(Nodes)
+as defined in these YAMLs. Following this, a bootstrap mechanism is used to create a Kubernetes cluster on these VMs.
+While any of the several bootstrapping mechanisms can be used `kubeadm` is the popular option.
+
+**NOTE:** Workload clusters do not have any addons applied. Nodes in your workload clusters will be in the `NotReady`
+state until you apply addons for CNI plugin.
+  
+Once the target cluster is up the user can create the `Deployments`, `Services`, etc that handle the workload
+of the application.