*   You can now add "options" to the host's /etc/resolv.conf (or --resolv-conf), and they will be copied into pod's resolv.conf when dnsPolicy is Default. Being able to customize options is important because it is common to leverage options to fine-tune the behavior of DNS client. ([#54773](https://github.com/kubernetes/kubernetes/pull/54773),[...

    * API fields previously capable of storing and returning either `[]` and `null` via JSON API requests (for example, the Endpoints `subsets` field) can now store only `null` when created using the protobuf content-type or stored in etcd using protobuf serialization (the default in 1.6+). JSON API clients should tolerate `null` values for such fields, and treat `null` and `[]` as equivalent in meaning unless specifically documented otherwise...

- kube-controller-manager
  - The deprecated `--insecure-experimental-approve-all-kubelet-csrs-for-group` flag has been removed.
- kubelet
  - The deprecated `--google-json-key` flag has been removed. Remove the `--google-json-key` flag from kubelet invocations before upgrading. ([#69354](https://github.com/kubernetes/kubernetes/pull/69354), [@yujuhong](https://github.com/yujuhong))

API fields previously capable of storing and returning either `[]` and `null` via JSON API requests (for example, the Endpoints `subsets` field)
can now store only `null` when created using the protobuf content-type or stored in etcd using protobuf serialization (the default in 1.6).

- Added support for encoding and decoding types that implement the standard library interfaces `json.Marshaler`, `json.Unmarshaler`, `encoding.TextMarshaler`, or `encoding.TextUnmarshaler` to and from CBOR by transcoding. ([#132935](https://github.com/kubernetes/kubernetes/pull/132935), [@benluddy](https://github.com/benluddy))

### (No, really, you MUST read this before you upgrade)

  If you are using docker manifests there are not visible changes. ([#80266](https://github.com/kubernetes/kubernetes/pull/80266), [@javier-b-perez](https://github.com/javier-b-perez))
- kubeadm now deletes the bootstrap-kubelet.conf file after TLS bootstrap

- Improved how the API server responds to **list** requests where the response format negotiates to JSON. 
List responses in JSON are marshalled one element at a time, drastically reducing the memory needed to serve 

### API Change

- Protobuf serialization of metav1.MicroTime timestamps (used in `Lease` and `Event` API objects) has been corrected to truncate to microsecond precision, to match the documented behavior and JSON/YAML serialization. Any existing persisted data is truncated to microsecond when read from etcd. ([#111936](https://github.com/kubernetes/kubernetes/pull/111936), [@haoruan](https://github.com/haoruan)) [SIG API Machinery]

- Kubeadm: enhanced the "patches" functionality to be able to patch kubelet config files containing `v1beta1.KubeletConfiguration`. The new patch target is called `kubeletconfiguration` (e.g. patch file `kubeletconfiguration+json.json`).This makes it possible to apply node specific KubeletConfiguration options during `init`, `join` and `upgrade`, while the main `KubeletConfiguration` that is passed to `init` as part of the `--config` file can still act as the global stored in...