* apiserver: fixes handling and logging of panics in REST handlers to prevent crashes ([#71076](https://github.com/kubernetes/kubernetes/pull/71076), [@liggitt](https://github.com/liggitt))
* Fixes an issue with stuck connections handling error responses ([#71419](https://github.com/kubernetes/kubernetes/pull/71419), [@liggitt](https://github.com/liggitt))

* Fix handling tombstones in pod-disruption-budged controller. ([#83951](https://github.com/kubernetes/kubernetes/pull/83951), [@zouyee](https://github.com/zouyee))

- Fixes calculating the requeue time in the cronjob controller, which results in properly handling failed/stuck jobs ([#121327](https://github.com/kubernetes/kubernetes/pull/121327), [@soltysh](https://github.com/soltysh)) [SIG Apps]

## Changelog since v1.18.3

## Changes by Kind

### API Change

- Resolve regression in metadata.managedFields handling in update/patch requests submitted by older API clients ([#92007](https://github.com/kubernetes/kubernetes/pull/92007), [@apelisse](https://github.com/apelisse)) [SIG API Machinery and Testing]

### Feature

* When using IP aliases, use a secondary range rather than subnetwork to reserve cluster IPs. ([#51690](https://github.com/kubernetes/kubernetes/pull/51690), [@bowei](https://github.com/bowei))
* IPAM controller unifies handling of node pod CIDR range allocation. ([#51374](https://github.com/kubernetes/kubernetes/pull/51374), [@bowei](https://github.com/bowei))
    * It is intended to supersede the logic that is currently in range_allocator

- Fixed `kube-proxy` panicking on exit when the `Node` object changed its `PodCIDR`. ([#120375](https://github.com/kubernetes/kubernetes/pull/120375), [@pegasas](https://github.com/pegasas))
- Fixed bugs in handling of server-side apply, create, and update API requests for objects containing duplicate items in keyed lists.

- Bump debian-base to v1.0.1 and debian-iptables to v11.0.3 ([#88882](https://github.com/kubernetes/kubernetes/pull/88882), [@tallclair](https://github.com/tallclair)) [SIG API Machinery, Cluster Lifecycle, Release and Testing]

## Changes since v1.2.1

### Other notable changes

* Trusty: Update heapster manifest handling code ([#23434](https://github.com/kubernetes/kubernetes/pull/23434), [@andyzheng0831](https://github.com/andyzheng0831))

    Kubernetes-managed containers on the node.
  * It is not compatible with CNI plugins that do not conform to the
    [error handling behavior in the spec](https://github.com/containernetworking/cni/blob/master/SPEC.md#network-configuration-list-error-handling).
    The plugins are being updated to resolve this issue ([#43488](https://github.com/kubernetes/kubernetes/issues/43488)).

   ([#122334](https://github.com/kubernetes/kubernetes/pull/122334), [@carlory](https://github.com/carlory))