Add documentation around KubeadmControlPlanes

Signed-off-by: Chuck Ha <[email protected]>

docs/book/src/SUMMARY.md

@@ -11,6 +11,7 @@
         - [Generating a Kubeconfig](./tasks/certs/generate-kubeconfig.md)
     - [Upgrade](./tasks/upgrade.md)
     - [Configure a MachineHealthCheck](./tasks/healthcheck.md)
+    - [Kubeadm based control plane management](./kubeadm-control-plane.md)
 - [clusterctl CLI](./clusterctl/overview.md)
     - [clusterctl Commands](clusterctl/commands/commands.md)
         - [init](clusterctl/commands/init.md)

docs/book/src/tasks/kubeadm-control-plane.md

@@ -0,0 +1,28 @@
+# Kubeadm control plane
+
+Using the Kubeadm control plane type to manage a control plane provides several ways to upgrade control plane machines.
+
+## Upgrading
+
+The high level steps to fully upgrading a workload cluster are to first upgrade the control plane and then upgrade
+the worker machines.
+
+### Upgrading workload machines managed by a `MachineDeployment`
+
+It is recommended to manage workload machines with a `MachineDeployment` as this will transparently manage `MachineSet`s
+and `Machine`s to allow for a seamless scaling experience. A modification to the `MachineDeployment`s spec will begin a
+rolling update of the workload machines.
+
+### How to upgrade the underlying machine image
+
+To upgrade the control plane machines underlying machine images, the `MachineTemplate` resource referenced by the
+`KubeadmControlPlane` must be changed. Since `MachineTemplate` resources are immutable, the recommended approach is to
+copy the existing `MachineTemplate`, modify the necessary values, create the new `MachineTemplate` on the management
+cluster, and finally, modify the existing `KubeadmControlPlane` resource to reference the new `MachineTemplate`
+resource. This will trigger a rolling update of the control plane using the new values found in the `MachineTemplate`.
+
+### How to upgrade the Kubernetes control plane version
+
+To upgrade the Kubernetes control plane version, which will likely, depending on the provider, also upgrade the
+underlying machine image, make a modification to the `KubeadmControlPlane` resource's `Version` field. This will trigger
+a rolling upgrade of the control plane.