pre-1.0 to 1.6 kubelet is not supported.
* Fluentd was migrated to Daemon Set, which targets nodes with
  beta.kubernetes.io/fluentd-ds-ready=true label. If you use fluentd in your
  cluster please make sure that the nodes with version 1.6+ contains this
  label.

### kubectl
* Running `kubectl taint` (alpha in 1.5) against a 1.6 server requires upgrading kubectl to version 1.6

- Kube-apiserver: fixed a bug returning inconsistent results from list requests which set a field or label selector and set a paging limit ([#94002](https://github.com/kubernetes/kubernetes/pull/94002), [@wojtek-t](https://github.com/wojtek-t)) [SIG API Machinery]

  // +optional
  optional int32 minReadySeconds = 4;

  // Selector is a label query over pods that should match the Replicas count.
  // If Selector is empty, it is defaulted to the labels present on the Pod template.
  // Label keys and values that must match in order to be controlled by this replication
  // controller, if empty defaulted to labels on Pod template.

  - cAdvisor json endpoints have been deprecated since 1.15. ([#78504](https://github.com/kubernetes/kubernetes/pull/78504), [@dashpole](https://github.com/dashpole))

* This change applies zone labels to vSphere Volumes automatically. The zone labels are visible on the PV: ([#72687](https://github.com/kubernetes/ku...

  - Make "kubeadm upgrade apply" add the "node-role.kubernetes.io/control-plane" label on existing nodes that only have the "node-role.kubernetes.io/master" label during upgrade.
  - Please adapt your tooling built on top of kubeadm to use the "node-role.kubernetes.io/control-plane" label.

- When specifying an invalid value for a label, it was not always clear which label the value was specified for. Starting with this release, the label's key is included in such error messages, which makes debugging easier. ([#77144](https://github.com/kubernetes/kubernetes/pull/77144), [@kenegozi](https://github.com/kenegozi))

* The ScaleIO volume plugin can now read the SDC GUID value as node label scaleio.sdcGuid; if binary drv_cfg is not installed, the plugin will still work properly; if node label not found, it defaults to drv_cfg if installed. ([#50780](https://github.com/kubernetes/kubernetes/pull/50780), [@vladimirvivien](https://github.com/vladimirvivien))

  - Use of the `--node-labels` flag to set labels under the `kubernetes.io/` and `k8s.io/` prefix will be subject to restriction by the `NodeRestriction` admission plugin in future releases. [See admission plugin documentation](https://kubernetes.io/docs/reference/access-authn-authz/admission-controllers/#noderestriction) for allowed labels. ([#68267](https://github.com/kubernetes/kubernetes/pull/68267), [@liggitt](https://github.com/liggitt))...

- '`metav1.LabelSelectors` specified in API objects are now validated to ensure
  they do not contain invalid label values that will error at time of use. Existing
  invalid objects can be updated, but new objects are required to contain valid
  label selectors.'
   ([#113699](https://github.com/kubernetes/kubernetes/pull/113699), [@liggitt](https://github.com/liggitt))