- Fixed issue with Winkernel Proxier - IPV6 load balancer policies were missing when service was configured with `ipFamilyPolicy`: `RequireDualStack` ([#115503](https://github.com/kubernetes/kubernetes/pull/115503), [@princepereira](https://github.com/princepereira))

			globalActiveCred)
		warnings = append(warnings, color.YellowBold(msg))
	}

	// Initialize users credentials and policies in background right after config has initialized.
	go func() {
		bootstrapTrace("globalIAMSys.Init", func() {
			globalIAMSys.Init(GlobalContext, newObject, globalEtcdClient, globalRefreshIAMInterval)
		})

- `kubelet` now allows pods to use the `net.ipv4.tcp_keepalive_time` sysctl by default
  and the minimal kernel version is 4.5; Pod Security Admission allows this sysctl

* Add support for PodSecurityPolicy on GCE: `ENABLE_POD_SECURITY_POLICY=true` enables the admission controller, and installs policies for default addons. ([#52367](https://github.com/kubernetes/kubernetes/pull/52367), [@tallclair](https://github.com/tallclair))

- Added a `--topology-manager-policy-options` flag to the kubelet to support fine tuning the topology manager policies. The first policy option, `prefer-closest-numa-nodes`, allows these policies to favor sets of NUMA nodes with shorter distance between nodes when making admission decisions. ([#112914](https://github.com/kubernetes/kubernetes/pull/112914), [@PiotrProkop](https://github.com/PiotrProkop))...

  - Expanded support for federated hybrid-cloud resources including ReplicaSets, Secrets, Namespaces and Events.
- **Security**
  - Increased pod-level security granularity (eg: Container Image Policies, AppArmor and `sysctl` support)
  - Increased cluster-level security granularity (eg: Access Review API)

## Features

  * `kubectl get podsecuritypolicies -o yaml > psp.yaml`
2. Review and delete any PodSecurityPolicy objects you do not want all pod-creating users to be able to use (NOTE: Privileged users that were making use of those policies will also lose access to those policies). For example:
  * `kubectl delete podsecuritypolicies/my-privileged-policy`
3. After upgrading to 1.5.5, re-create the exported PodSecurityPolicy objects:
  * `kubectl create -f psp.yaml`

## Changes to API Resources
### ABAC
* ABAC policies using `"user":"*"` or `"group":"*"` to match all users or groups will only match authenticated requests. To match unauthenticated requests, ABAC policies must explicitly specify `"group":"system:unauthenticated"` ([#38968](https://github.com/kubernetes/kubernetes/pull/38968), [@liggitt](https://github.com/liggitt))

  This feature is in alpha. ([#122887](https://github.com/kubernetes/kubernetes/pull/122887), [@jpbetz](https://github.com/jpbetz))
- `ValidatingAdmissionPolicy` now supports type checking policies that utilize variables. ([#123083](https://github.com/kubernetes/kubernetes/pull/123083), [@jiahuif](https://github.com/jiahuif))

### Documentation

#### Cluster Selection