k0smotron as Cluster API provider#

k0smotron can act as a Cluster API provider in several different roles.

Control Plane provider - in-cluster#

When k0smotron acts as a control plane provider it will create and manage the cluster control plane within the management cluster, just as in the standalone case.

Control Plane - out-of-cluster#

k0smotron can function also as a "traditional" contol plane provider where the control plane is running on CAPI managed Machiness.

Bootstrap provider#

k0smotron can also act as a bootstrap provider for worker nodes you want to manage via Cluster API. When k0smotron detects a new node that needs to be added to the cluster it will automatically create a new join token needed for the node and creates the provisioning cloud-init script for the node. Once Cluster API controllers sees the node initialization script in place (in a secret) the infrastructure provider will create the needed resources (usually VMs in cloud provider infrastructure) with the k0smotron created cloud-init script.

Remote Machine provider#

k0smotron also provides a ClusterAPI provider to manage and bootstrap cluster Machines remotely via SSH connection. This allows managing the clusters in environment where there's no existing ClusterAPi provider available. Such environments could be for example bare metal environments.

Cluster autoscaling#

Cluster Autoscaler works with ClusterAPI. You need to deploy an "instance" of autoscaler per child cluster in order for it to work properly. If you deploy autoscaler via Helm, here's some values to look out:

Value	Why?
`autodiscovery.clusterName`	Select the child cluster you want to autoscale. E.g. `my-cluster`
`cloudProvider`	Set to `clusterapi` to make autoscaler work with ClusterAPI
`clusterAPIKubeconfigSecret`	Set to the kubeconfig secret created by CAPI. E.g. `my-cluster-kubeconfig`
`clusterAPIMode`	Set to `kubeconfig-incluster`. Essentially this tells that the child cluster API is accessed with the kubeconfig from the secret and management cluster via `incluster` kubeconfig

RBAC finetuning needed with Helm deployed autoscaler

The Helm chart does not take into account the need for autoscaler to access the implementation specific resources in infrastructure.cluster.x-k8s.io group. To fix that you need to modify* the ClusterRole to include e.g.

- verbs:
   - get
   - list
   - update
   - watch
 apiGroups:
   - infrastructure.cluster.x-k8s.io
 resources:
   - '*' # You can of course limit this to your specific infrastructure types only, e.g. `AWSMachineDeployment` etc.

*) Happy to get feedback whether there's a better workaround for this.