* The Rackspace cloud provider has been removed after a long deprecation period. It was deprecated because it duplicates a lot of the OpenStack logic and can no longer be maintained. Please use the OpenStack cloud provider instead. ([#52855](https://github.com/kubernetes/kubernetes/pull/52855), [@NickrenREN](https://github.com/NickrenREN))

- Fixed a regression in default configurations, which enabled PodDisruptionConditions by default, 
  that prevented the control plane's pod garbage collector from deleting pods that contained duplicated field keys (env. variables with repeated keys or container ports). ([#121380](https://github.com/kubernetes/kubernetes/pull/121380), [@mimowo](https://github.com/mimowo)) [SIG Apps, Auth, Scheduling and Testing]

- EndpointSlice controllers are less likely to create duplicate EndpointSlices. ([#100103](https://github.com/kubernetes/kubernetes/pull/100103), [@robscott](https://github.com/robscott)) [SIG Apps and Network]

- kube-proxy: a configuration file specified via `--config` is now loaded with strict deserialization, which fails if the config file contains duplicate or unknown fields. This protects against accidentally running with config files that are malformed, mis-indented, or have typos in field names, and getting unexpected behavior. ([#82927](https://github.com/kubernetes/kubernetes/pull/82927), [@ob...

* Fixes an issue with RBAC reconciliation that could cause duplicated subjects in some bootstrapped rolebindings on each restart of the API server. ([#53239](https://github.com/kubernetes/kubernetes/pull/53239), [@enj](https://github.com/enj))

- Fixed a regression in default configurations, which enabled PodDisruptionConditions by default, 
  that prevented the control plane's pod garbage collector from deleting pods that contained duplicated field keys (env. variables with repeated keys or container ports). ([#121379](https://github.com/kubernetes/kubernetes/pull/121379), [@mimowo](https://github.com/mimowo)) [SIG Apps, Auth, Node, Scheduling and Testing]

### SIG Storage

- The AllowedTopologies field inside StorageClass is now validated against set and map semantics. Specifically, there cannot be duplicate TopologySelectorTerms, MatchLabelExpressions keys, or TopologySelectorLabelRequirement Values. ([#66843](https://github.com/kubernetes/kubernetes/pull/66843), [@verult](https://github.com/verult))

In particular, the following storage features are moving to GA in Kubernetes 1.18:
- Raw Block Support: Allow volumes to be surfaced as block devices inside containers instead of just mounted filesystems.
- Volume Cloning: Duplicate a PersistentVolumeClaim and underlying storage volume using the Kubernetes API via CSI.
- CSIDriver Kubernetes API Object: Simplifies CSI driver discovery and allows CSI Drivers to customize Kubernetes behavior.

* kubectl and client-go now detect duplicated names for user, cluster and context when loading kubeconfig and report this condition as an error.  ([#60464](https://github.com/kubernetes/kubernetes/pull/60464), [@roycaihw](https://github.com/roycaihw))

- Improvements were made to `kubeadm reset` related to cleaning  etcd and notifying the user about the state of iptables.
- kubeadm commands now print warnings if input YAML documents contain unknown or duplicate fields.
- kubeadm now properly recognizes Docker 18.09.0 and newer, but still treats 18.06 as the default supported version.
- kubeadm now automatically sets the `--pod-infra-container-image` flag when starting the kubelet.