Added info on ClusterClass use

Signed-off-by: Patryk Strusiewicz-Surmacki <[email protected]>

docs/user-guide/src/capm3/clusterclass.md

@@ -0,0 +1,89 @@
+# Using ClusterClass with CAPM3
+
+ClusterClass is a feature of Cluster API that enables the cluster operators to
+create multiple clusters using a single general template. You can find detailed
+explanation of how to use a `ClusterClass` in the
+[Cluster API documentation](https://github.com/kubernetes-sigs/cluster-api/blob/main/docs/proposals/20210526-cluster-class-and-managed-topologies.md)
+
+## Prerequisites
+
+### ClusterClass support enabled in CAPI
+
+To use ClusterClass with CAPM3, experimental feature `ClusterClass` has to be
+enabled in CAPI deployment. You can find more info on how to enable ClusterClass
+support [in The Cluster API Book](https://cluster-api.sigs.k8s.io/tasks/experimental-features/cluster-class/).
+
+## Deploying cluster using ClusterClass
+
+### Deploying a ClusterClass
+
+To create ClusterClass for CAPM3 a few objects has to be deployed in the
+management-cluster:
+
+- Metal3ClusterTemplate - a template that will be used by ClusterClass
+controller to instantiate the cluster.
+
+- KubeadmControlPlaneTemplate - a template used to create Kubeadm Control Plane
+for the instantiated cluster.
+
+- Metal3MachineTemplate - templates that will be used to create Metal3Machine
+objects. Can be defined saparately for control plane and worker nodes.
+
+- KubeadmConfigTemplate - a template for Kubeadm config.
+
+- ClusterClass - the final object that references above objects and consolidates
+them into single cluster template definition.
+
+You can find example of those objects
+[in the example file available on the CAPM3 repository](https://github.com/metal3-io/cluster-api-provider-metal3/blob/main/examples/templates/clusterclass.yaml).
+
+### Deploying a Cluster
+
+Definitions described above can be used to deploy multiple clusters. However
+some resources has to be deployed specifically for the cluster:
+
+- Metal3DataTemplate - should be created for both worker and control plane nodes
+in the cluster
+
+- IPPools - should be created per cluster if required.
+
+- Cluster - used to instantiate cluster using `ClusterClass`. You can change
+cluster behavior by overriding variables defined in the `ClusterClass`.
+
+Example definitions of those resources
+[can be found in the CAPM3 repository](https://github.com/metal3-io/cluster-api-provider-metal3/blob/main/examples/templates/cluster.yaml).
+
+## Tilt based development environment
+
+If you want to further develop or test ClusterClass support you can use Tilt
+environment.
+
+1. Clone CAPM3 repository.
+
+    ```shell
+    git clone https://github.com/metal3-io/cluster-api-provider-metal3.git
+    ```
+
+1. Generate Tilt settings that will enable ClusterClass support in CAPI.
+
+    ```shell
+    make tilt-settings-clusterclass
+    ```
+
+1. Start Tilt.
+
+    ```shell
+    make tilt-up
+    ```
+
+1. Generate ClusterClass based example.
+
+    ```shell
+    make generate-examples-clusterclass
+    ```
+
+1. Deploy example `ClusterClass`, `Cluster` and all the dependencies.
+
+    ```shell
+    make deploy-examples-clusterclass
+    ```