Cluster add-ons

Overview

Cluster add-ons are resources like Services and Deployments (with pods) that are shipped with the Kubernetes binaries and are considered an inherent part of the Kubernetes clusters.

There are currently two classes of add-ons:

• Add-ons that will be reconciled.
• Add-ons that will be created if they don't exist.

More details could be found in addon-manager/README.md.

Cooperating Horizontal / Vertical Auto-Scaling with "reconcile class addons"

"Reconcile" class addons will be periodically reconciled to the original state given by the initial config. In order to make Horizontal / Vertical Auto-scaling functional, the related fields in config should be left unset. More specifically, leave replicas in ReplicationController / Deployment / ReplicaSet unset for Horizontal Scaling, leave resources for container unset for Vertical Scaling. The periodic reconcile won't clobbered these fields, hence they could be managed by Horizontal / Vertical Auto-scaler.

Add-on naming

The suggested naming for most of the resources is <basename> (with no version number). Though resources like Pod, ReplicationController and DaemonSet are exceptional. It would be hard to update Pod because many fields in Pod are immutable. For ReplicationController and DaemonSet, in-place update may not trigger the underlying pods to be re-created. You probably need to change their names during update to trigger a complete deletion and creation.

Acknowledgement

Forked from kubernetes/kubernetes and periodically updated.

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