ef87482923
Automatic merge from submit-queue (batch tested with PRs 53106, 52193, 51250, 52449, 53861). 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>. kube-dns-anti-affinity: kube-dns never-co-located-in-the-same-node **What this PR does / why we need it**: This is upstreaming the kubernetes/kops#2705 pull request by @jamesbucher that was originally against [kops](github.com/kubernetes/kops). Please see kubernetes/kops#2705 for more details, including a lengthy discussion. Briefly, given the constraints of how the system works today: + if you need multiple DNS pods primarily for availability, then requiredDuringSchedulingIgnoredDuringExecution makes sense because putting more than one DNS pod on the same node isn't useful + if you need multiple DNS pods primarily for performance, then preferredDuringScheduling IgnoredDuringExecution makes sense because it will allow the DNS pods to schedule even if they can't be spread across nodes **Which issue this PR fixes** fixes kubernetes/kops#2693 **Release note**: ```release-note Improve resilience by annotating kube-dns addon with podAntiAffinity to prefer scheduling on different nodes. ```
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.