- HPA controller starts to expose metrics from the kube-controller-manager.\n- `reconciliations_total`: Number of reconciliation of HPA controller. \n- `reconciliation_duration_seconds`: The time(seconds) that the HPA controller takes to reconcile once. ([#116010](https://github.com/kubernetes/kubernetes/pull/116010), [@sanposhiho](https://github.com/sanposhiho))

- Horizontal Pod Autoscaler default update interval has been increased from 30s to 15s, improving HPA reaction time for metric changes. ([#68021](https://github.com/kubernetes/kubernetes/pull/68021), [@krzysztof-jastrzebski](https://github.com/krzysztof-jastrzebski))

      - [Storage](#storage)
    - [Cluster Federation](#cluster-federation)
      - [[alpha] Federated Jobs](#alpha-federated-jobs)
      - [[alpha] Federated Horizontal Pod Autoscaling (HPA)](#alpha-federated-horizontal-pod-autoscaling-hpa)
    - [Node Components](#node-components)
      - [Autoscaling and Metrics](#autoscaling-and-metrics)
        - [Cluster Autoscaler](#cluster-autoscaler)

- Added HPA support to pod-level resource specifications. When the pod-level resource feature was enabled, HPAs configured with `Resource` type metrics calculated the pod resources from `pod.Spec.Resources` field, if specified. ([#132430](https://github.com/ku...

* When HPAScaleToZero feature gate is enabled HPA supports scaling to zero pods based on object or external metrics. HPA remains active as long as at least one metric value available. ([#74526](https://github.com/kubernetes/kubernetes/pull/74526), [@DXist](https://github.com/DXist))
    * To downgrade the cluster to version that does not support scale-to-zero feature:

 - Fix HPA when using init containers and CRI-O ([#90901](https://github.com/kubernetes/kubernetes/pull/90901), [@joelsmith](https://github.com/joelsmith)) [SIG Node]

*   Fixed a set of minor issues with Cluster Autoscaler 1.0.1 ([#54298](https://github.com/kubernetes/kubernetes/pull/54298),[ @mwielgus](https://github.com/mwielgus))
*   HPA tolerance is now configurable by setting the `horizontal-pod-autoscaler-tolerance` flag. ([#52275](https://github.com/kubernetes/kubernetes/pull/52275),[ @mattjmcnaughton](https://github.com/mattjmcnaughton))

* Fix udp service blackhole problem when number of backends changes from 0 to non-0 ([#48524](https://github.com/kubernetes/kubernetes/pull/48524), [@freehan](https://github.com/freehan))
* hpa: Prevent scaling below MinReplicas if desiredReplicas is zero ([#48997](https://github.com/kubernetes/kubernetes/pull/48997), [@johanneswuerbach](https://github.com/johanneswuerbach))

* Do not count failed pods as unready in HPA controller ([#60648](https://github.com/kubernetes/kubernetes/pull/60648), [@bskiba](https://github.com/bskiba))

* HorizontalPodAutoscaler is no longer supported in extensions/v1beta1 version. Use autoscaling/v1 instead. ([#35782](https://github.com/kubernetes/kubernetes/pull/35782), [@piosz](https://github.com/piosz))
* Fixes an HPA-related panic due to division-by-zero. ([#39694](https://github.com/kubernetes/kubernetes/pull/39694), [@DirectXMan12](https://github.com/DirectXMan12))

### Certificates