* Old behavior:
      * environment variables explicitly whitelisted via --docker-env-metadata-whitelist were exported as `container_env_*=*`. Default is zero so by default non were exported
      * all docker labels were exported as `container_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))

  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

* AWS: Allow cross-region image pulling with ECR ([#24369](https://github.com/kubernetes/kubernetes/pull/24369), [@therc](https://github.com/therc))
* Automatically add node labels beta.kubernetes.io/{os,arch} ([#23684](https://github.com/kubernetes/kubernetes/pull/23684), [@luxas](https://github.com/luxas))

#### Cluster Selection
* [alpha] Federation [ClusterSelector annotation](https://kubernetes.io/docs/tasks/administer-federation/cluster/#clusterselector-annotation) to direct objects to federated clusters with matching labels.


### **Instrumentation**
#### Core Metrics API

- '`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))