Cluster API bootstrap provider MicroK8s

What is the Cluster API bootstrap provider MicroK8s?

Cluster API bootstrap provider MicroK8s (CABPM) is a component responsible for generating a cloud-init script to turn a Machine into a Kubernetes Node. This implementation uses MicroK8s for Kubernetes bootstrap.

Resources

• CABPM Repository
• Official MicroK8s site

CABPM configuration options

MicroK8s defines a MicroK8sControlPlane definition as well as the MachineDeployment to configure the control plane and worker nodes respectively. The MicroK8sControlPlane is linked in the cluster definition as shown in the following example:

apiVersion: cluster.x-k8s.io/v1beta1
kind: Cluster
spec:
  controlPlaneRef:
    apiVersion: controlplane.cluster.x-k8s.io/v1beta1
    kind: MicroK8sControlPlane
    name: capi-aws-control-plane

A control plane manifest section includes the Kubernetes version, the replica number as well as the MicroK8sConfig:

apiVersion: controlplane.cluster.x-k8s.io/v1beta1
kind: MicroK8sControlPlane
spec:
  controlPlaneConfig:
    initConfiguration:
      addons:
      - dns
      - ingress
  replicas: 3
  version: v1.23.0
  ......

The worker nodes are configured through the MachineDeployment object:

apiVersion: cluster.x-k8s.io/v1beta1
kind: MachineDeployment
metadata:
  name: capi-aws-md-0
  namespace: default
spec:
  clusterName: capi-aws
  replicas: 2
  selector:
    matchLabels: null
  template:
    spec:
      clusterName: capi-aws
      version: v1.23.0     
      bootstrap:
        configRef:
          apiVersion: bootstrap.cluster.x-k8s.io/v1beta1
          kind: MicroK8sConfigTemplate
          name: capi-aws-md-0
......
---
apiVersion: bootstrap.cluster.x-k8s.io/v1beta1
kind: MicroK8sConfigTemplate
metadata:
  name: capi-aws-md-0
  namespace: default
spec:
  template:
    spec: {}

In both the MicroK8sControlPlane and MicroK8sConfigTemplate you can set a MicroK8sConfig object. In the MicroK8sControlPlane case MicroK8sConfig is under MicroK8sConfig.spec.controlPlaneConfig whereas in MicroK8sConfigTemplate it is under MicroK8sConfigTemplate.spec.template.spec.

Some of the configuration options available via MicroK8sConfig are:

• MicroK8sConfig.spec.initConfiguration.joinTokenTTLInSecs: the time-to-live (TTL) of the token used to join nodes, defaults to 10 years.
• MicroK8sConfig.spec.initConfiguration.httpsProxy: the https proxy to be used, defaults to none.
• MicroK8sConfig.spec.initConfiguration.httpProxy: the http proxy to be used, defaults to none.
• MicroK8sConfig.spec.initConfiguration.noProxy: the no-proxy to be used, defaults to none.
• MicroK8sConfig.spec.initConfiguration.addons: the list of addons to be enabled, defaults to dns.
• MicroK8sConfig.spec.clusterConfiguration.portCompatibilityRemap: option to reuse the security group ports set for kubeadm, defaults to true.

How does CABPM work?

The main purpose of the MicroK8s bootstrap provider is to translate the users needs to a number of cloud-init files applicable for each type of cluster nodes. There are three types of cloud-inits:

• The first node cloud-init. That node will be a control plane node and will be the one where the addons are enabled.
• The control plane node cloud-init. The control plane nodes need to join a cluster and contribute to its HA.
• The worker node cloud-init. These nodes join the cluster as workers.

The cloud-init scripts are saved as secrets that then the infrastructure provider uses during the machine creation. For more information on cloud-init options, see cloud config examples.