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Cluster extensions#

k0s allows users to use extensions to extend cluster functionality.

At the moment the only supported type of extensions is helm based charts.

The default configuration has no extensions.

Helm based extensions#

Configuration example#

helm:
  repositories:
  - name: stable
    url: https://charts.helm.sh/stable
  - name: prometheus-community
    url: https://prometheus-community.github.io/helm-charts
  charts:
  - name: prometheus-stack
    chartname: prometheus-community/prometheus
    version: "11.16.8"
    values: |
      storageSpec:
        emptyDir:
          medium: Memory
    namespace: default
  # We don't need to specify the repo in the repositories section for OCI charts
  - name: oci-chart
    chartname: oci://registry:8080/chart
    version: "0.0.1"
    values: ""
    namespace: default
  # Other way is to use local tgz file with chart
  # the file must exist all controller nodes
  - name: tgz-chart
    chartname: /tmp/chart.tgz
    version: "0.0.1"
    values: ""
    namespace: default

By using the configuration above, the cluster would:

  • add stable and prometheus-community chart repositories
  • install the prometheus-community/prometheus chart of the specified version to the default namespace.

The chart installation is implemented by using CRD helm.k0sproject.io/Chart. For every given helm extension the cluster creates a Chart CRD instance. The cluster has a controller which monitors for the Chart CRDs, supporting the following operations:

  • install
  • upgrade
  • delete

For security reasons, the cluster operates only on Chart CRDs instantiated in the kube-system namespace, however, the target namespace could be any.

CRD definition#

apiVersion: helm.k0sproject.io/v1beta1
kind: Chart
metadata:
  creationTimestamp: "2020-11-10T14:17:53Z"
  generation: 2
  labels:
    k0s.k0sproject.io/stack: helm
  name: k0s-addon-chart-test-addon
  namespace: kube-system
  resourceVersion: "627"
  selfLink: /apis/helm.k0sproject.io/v1beta1/namespaces/kube-system/charts/k0s-addon-chart-test-addon
  uid: ebe59ed4-1ff8-4d41-8e33-005b183651ed
spec:
  chartName: prometheus-community/prometheus
  namespace: default
  values: |
    storageSpec:
      emptyDir:
        medium: Memory
  version: 11.16.8
status:
  appVersion: 2.21.0
  namespace: default
  releaseName: prometheus-1605017878
  revision: 2
  updated: 2020-11-10 14:18:08.235656 +0000 UTC m=+41.871656901
  version: 11.16.8

The Chart.spec defines the chart information.

The Chart.status keeps the information about the last operation performed by the operator.