* Upgrade the default etcd server version to 3.1.12 to pick up critical etcd "mvcc "unsynced" watcher restore operation" fix. ([#60998](https://github.com/kubernetes/kubernetes/pull/60998), [@jpbetz](https://github.com/jpbetz))

garbage collecting other resources if a given resource cannot be listed or watched. Any objects in the unsynced resource type with owner references with `blockOwnerDeletion: true` will not be known to the garbage collector. Use of `blockOwnerDeletion` has always been best-effort and racy on startup and object creation. With this fix, it continues to be best-effort for resources that cannot be synced by the garbage collector controller. ([#125796](https://github.com/kubernetes/kubernetes/pull/125796),...

## Changelog since v1.18.15

## Changes by Kind

### Bug or Regression

- Avoid marking node as Ready until node has synced with API servers at least once ([#99034](https://github.com/kubernetes/kubernetes/pull/99034), [@ehashman](https://github.com/ehashman)) [SIG Node]

* Moved qos to api.helpers. ([#44906](https://github.com/kubernetes/kubernetes/pull/44906), [@k82cn](https://github.com/k82cn))

* Fix issue with the resource quota controller causing add quota to be resynced at the wrong ([#45685](https://github.com/kubernetes/kubernetes/pull/45685), [@derekwaynecarr](https://github.com/derekwaynecarr))

- The EndpointSlice controller now waits for EndpointSlice and Node caches to be synced before starting. ([#94086](https://github.com/kubernetes/kubernetes/pull/94086), [@robscott](https://github.com/robscott)) [SIG Apps and Network]

- Shared informers now correctly propagate whether they are synced or not. Individual informer handlers may now check if they are synced or not (new `HasSynced` method). Library support is added to assist controllers in tracking whether their own work is completed for items in the initial list (`AsyncTracker`). ([#113985](https://github.com/kuber...

    * [prometheus-to-sd addon] Bump prometheus-to-sd to 0.3.1 to pick up security fixes, bug fixes and new features.
    * [event-exporter addon] Bump event-exporter to 0.2.3 to pick up security fixes.

### Bug or Regression

- Aggregate errors when putting vmss ([#98350](https://github.com/kubernetes/kubernetes/pull/98350), [@nilo19](https://github.com/nilo19)) [SIG Cloud Provider]
- Avoid marking node as Ready until node has synced with API servers at least once ([#97995](https://github.com/kubernetes/kubernetes/pull/97995), [@ehashman](https://github.com/ehashman)) [SIG Node]

* Bump event-exporter to 0.2.2 to pick up security fixes. ([#66157](https://github.com/kubernetes/kubernetes/pull/66157), [@loburm](https://github.com/loburm))

- A PersistentVolumeClaim may not have been synced to the controller local cache in time if the PersistentVolumeis bound by an external PV binder (such as kube-scheduler), so Kubernetes will now double check if PVC is not found in order to prevent the volume from being incorrectly reclaimed. ([#6...