* fixed bugs and improved performance in Stackdriver Sink
* fluentd-gcp addon: Fix a bug in the event-exporter, when repeated events were not sent to Stackdriver. ([#50511](https://github.com/kubernetes/kubernetes/pull/50511), [@crassirostris](https://github.com/crassirostris))

* kube-proxy will emit "FailedToStartNodeHealthcheck" event when fails to start healthz server. ([#49267](https://github.com/kubernetes/kubernetes/pull/49267), [@MrHohn](https://github.com/MrHohn))

    * [event-exporter addon] Bump event-exporter to 0.2.3 to pick up security fixes.
* PVC may not be synced to controller local cache in time if PV is bound by external PV binder (e.g. kube-scheduler), double check if PVC is not found to prevent reclaiming PV wrongly. ([#67062](https://github.com/kubernetes/kubernetes/pull/67062), [@cofyc](https://github.com/cofyc))

- `client-go` event library allows customizing spam filtering function. 
  It is now possible to override `SpamKeyFunc`, which is used by event filtering to detect spam in the events. ([#103918](https://github.com/kubernetes/kubernetes/pull/103918), [@olagacek](https://github.com/olagacek))
- `client-go`, using log level 9, traces the following events of a HTTP request:
      - DNS lookup
      - TCP dialing

- kube-scheduler

  - Migrate scheduler to use v1beta1 Event API. any tool targeting scheduler events needs to use v1beta1 Event API ([#78447](https://github.com/kubernetes/kubernetes/pull/78447), [@yastij](https://github.com/yastij))

- kubeadm

- Improved the efficiency of NodeAdded QueueingHint by registering UpdateNodeTaint event for plugins that have NodeAdded event but don't have UpdateNodeTaint event. This ensures better requeuing efficiency and prevents Pods from being stuck in the unschedulable pod pool.

- Improved reboot event reporting. The kubelet will only emit one reboot Event when a server-level reboot 
is detected, even if the kubelet cannot write its status to the associated Node (which triggers a retry). ([#129151](https://github.com/kubernetes/kubernetes/pull/129151), [@rphillips](https://github.com/rphillips)) [SIG Node]

  - The `export` query parameter for list API calls, deprecated since v1.14, will be removed in v1.18.
  - The `series.state` field in the events.k8s.io/v1beta1 Event API is deprecated and will be removed in v1.18 ([#75987](https://github.com/kubernetes/kubernetes/pull/75987), [@yastij](https://github.com/yastij))

- kubeadm

- Updated the HPA controller so that it no longer emitted a `FailedRescale` event if a scale operation initially failed due to a conflict but succeeded after a retry; it now emitted a `SuccessfulRescale` event in this case. A `FailedRescale` event was still emitted if all retries were exhausted. ([#132007](https://github.com/kubernetes/kubernetes/pull/132007), [@AumPatel1](https://github.com/AumPatel1)) [SIG Apps...

- Fix a bug where events/v1 Events with similar event type and reporting instance were not aggregated by client-go. ([#112365](https://github.com/kubernetes/kubernetes/pull/112365), [@dgrisonnet](https://github.com/dgrisonnet)) [SIG API Machinery and Instrumentation]