Addon-manager

Addon-manager

The Addon-manager is a service running on the Kubernetes cluster's Master nodes designed to manage various Add-ons. It maintains all the extensions present in the $ADDON_PATH (which defaults to /etc/kubernetes/addons/) to ensure they always operate in the desired state.

Addon-manager supports two types of labels:

• For extensions tagged with addonmanager.kubernetes.io/mode=Reconcile, modifications through the API are not allowed. This means that:

  • Any changes made through the API will automatically revert to the configuration in /etc/kubernetes/addons/.

  • If an extension is deleted via the API, it will be automatically recreated from the configuration in /etc/kubernetes/addons/.

  • Removing configuration from /etc/kubernetes/addons/ will also delete the corresponding Kubernetes resources.

  • Essentially, modifications can only be made by adjusting the configuration in /etc/kubernetes/addons/.

• For extensions with the addonmanager.kubernetes.io/mode=EnsureExists label, there's only a check to ensure the existence of the extension without checking for configuration changes. In effect:

  • The configuration can be modified via the API without it being automatically reverted.

  • If an extension is deleted via the API, it will be automatically recreated from the configuration in /etc/kubernetes/addons/.

  • However, if the configuration is removed from /etc/kubernetes/addons/, the Kubernetes resources will not be deleted.

Deployment Method

Save the following YAML into the /etc/kubernetes/manifests/kube-addon-manager.yaml file on all Master nodes:

apiVersion: v1
kind: Pod
metadata:
  name: kube-addon-manager
  namespace: kube-system
  annotations:
    scheduler.alpha.kubernetes.io/critical-pod: ''
    seccomp.security.alpha.kubernetes.io/pod: 'docker/default'
  labels:
    component: kube-addon-manager
spec:
  hostNetwork: true
  containers:
  - name: kube-addon-manager
    # When updating version also bump it in:
    # - test/kubemark/resources/manifests/kube-addon-manager.yaml
    image: k8s.gcr.io/kube-addon-manager:v8.7
    command:
    - /bin/bash
    - -c
    - exec /opt/kube-addons.sh 1>>/var/log/kube-addon-manager.log 2>&1
    resources:
      requests:
        cpu: 3m
        memory: 50Mi
    volumeMounts:
    - mountPath: /etc/kubernetes/
      name: addons
      readOnly: true
    - mountPath: /var/log
      name: varlog
      readOnly: false
    env:
    - name: KUBECTL_EXTRA_PRUNE_WHITELIST
      value: {{kubectl_extra_prune_whitelist}}
  volumes:
  - hostPath:
      path: /etc/kubernetes/
    name: addons
  - hostPath:
      path: /var/log
    name: varlog

Source Code

The source code for Addon-manager is hosted at https://github.com/kubernetes/kubernetes/tree/master/cluster/addons/addon-manager.

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Addon-manager: A Kubernetes Cluster Maestro

Meet the Addon-manager, the essential service that diligently works in the background of Kubernetes Master nodes keeping add-ons in check. It's like a digital conductor for the $ADDON_PATH – typically /etc/kubernetes/addons/ – maintaining a seamless operation of all extensions according to the script written for them.

The Addon-manager is adept at handling two kinds of labels that dictate extension behavior:

• Extensions marked with addonmanager.kubernetes.io/mode=Reconcile play by strict rules:

  • Try tweaking them through the API, and like a boomerang, they'll revert to their /etc/kubernetes/addons/ settings.

  • Delete them, and they magically reappear, thanks to the /etc/kubernetes/addons/ backup band.

  • However, pull their files from /etc/kubernetes/addons/, and it's curtains down for those Kubernetes resources.

  • The gist is, backstage configuration edits in /etc/kubernetes/addons/ are the only way to shuffle their act.

• Extensions donning the addonmanager.kubernetes.io/mode=EnsureExists label are the free spirits:

  • API modifications? Go ahead; no strings attached for a rollback.

  • Vanish through the API, and voilà, they make an encore using the /etc/kubernetes/addons/ script.

  • But should their part get axed from /etc/kubernetes/addons/, the show goes on without the Kubernetes resources curtain call.

Setting the Stage

To roll out the Addon-manager across the Master nodes' ensemble, simply script the following YAML into the /etc/kubernetes/manifests/kube-addon-manager.yaml of each maestro's station:

... [YAML content remains unchanged] ...

Ensemble's Composition

For those wanting to peek at the Addon-manager's score, the source code resides at https://github.com/kubernetes/kubernetes/tree/master/cluster/addons/addon-manager. Consider it an open invitation to see the magic behind the Kubernetes curtain!