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Automatic merge from submit-queue. If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>. Use results of kube-controller-manager leader election in addon manager **What this PR does / why we need it**: This adds leader election-like mechanism to addon manager. Currently, in a multi-master setup, upgrading one master will trigger a fight between addon managers on different masters, each forcing its own versions of addons. This leads to pod unavailability until all masters are upgraded to new version. To avoid implementing leader election in bash, results of leader election in kube-controller-manager are used. Long term, addon manager probably should be rewritten in a real prgramming language (probably Go), and then, real leader election should be implemented there. **Which issue(s) this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close the issue(s) when PR gets merged)*: I don't think there was an issue for this specifically, but this PR is related to https://github.com/kubernetes/kubernetes/issues/473 **Special notes for your reviewer**: **Release note**: ```release-note Addon manager supports HA masters. ```
Legacy Cluster add-ons
For more information on add-ons see the documentation.
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.