* Fixes an issue where `hack/local-up-cluster.sh` would fail on the API server start with ([#38898](https://github.com/kubernetes/kubernetes/pull/38898), [@deads2k](https://github.com/deads2k))

   ([#122276](https://github.com/kubernetes/kubernetes/pull/122276), [@pohly](https://github.com/pohly))
- Added a CBOR implementation of `runtime.Serializer`. Until CBOR graduates to Alpha, API servers will refuse to start if configured with CBOR support. ([#122881](https://github.com/kubernetes/kubernetes/pull/122881), [@benluddy](https://github.com/benluddy))
- Added a alpha feature, behind the `RelaxedEnvironmentVariableValidation` feature gate.

If this happens to you, you can wait at most 10 minutes for the replication controller to start a resync, the extra pods will then be deleted. Or, you can manually trigger a resync by change the replicas in the spec of the replication controller.

### kubectl delete: < v1.4.0 client vs >=v1.4.0 cluster