- If a client makes an API streaming requests and specifies an `application/json;as=Table` content type, the API server now responds with a 406 (Not Acceptable) error.

Certificate management has become more robust in 1.15, with kubeadm now seamlessly rotating all your certificates (on upgrades) before they expire. Check the [kubeadm documentation](https://github.com/kubernetes/website/blob/dev-1.15/content/en/docs/reference/setup-tools/kubeadm/kubeadm-alpha.md) for information on how to manage your certificates.

The kubeadm configuration file API is moving from v1beta1 to v1beta2 in 1.15.

- Client-ca bundles for the all generic-apiserver based servers will dynamically reload from disk on content changes ([#83579](https://github.com/kubernetes/kubernetes/pull/83579), [@deads2k](https://github.com/deads2k))

          <type>String</type>
        </field>
        <field>
          <description>
            <![CDATA[
            <p>The configuration as DOM object.</p>
            <p>By default, every element content is trimmed, but starting with Maven 3.1.0, you can add
            {@code xml:space="preserve"} to elements you want to preserve whitespace.</p>

* When performing a GET then PUT, the kube-apiserver must write the canonical representation of the object to etcd if the current value does not match. That allows external agents to migrate content in etcd from one API version to another, across different storage types, or across varying encryption levels. This fixes a bug introduced in 1.5 where we unintentionally stopped writing the newest data. ([#48394](https://github.com/kubernetes/kub...

### API Change

## Introduction to 1.9.0

Kubernetes version 1.9 includes new features and enhancements, as well as fixes to identified issues. The release notes contain a brief overview of the important changes introduced in this release. The content is organized by Special Interest Group ([SIG](https://github.com/kubernetes/community/blob/master/sig-list.md)).

- Build: Use debian-hyperkube-base@v1.0.0 image ([#91476](https://github.com/kubernetes/kubernetes/pull/91476), [@justaugustus](https://github.com/justaugustus)) [SIG Cluster Lifecycle, Network and Release]
- Content-type and verb for request metrics are now bounded to a known set. ([#89451](https://github.com/kubernetes/kubernetes/pull/89451), [@logicalhan](https://github.com/logicalhan)) [SIG API Machinery and Instrumentation]

- Improved handling of jsonpath expressions for `kubectl wait --for`. It is now possible to use simple filter expressions which match on a field's content. ([#118748](https://github.com/kubernetes/kubernetes/pull/118748), [@andreaskaris](https://github.com/andreaskaris))

* On GCI, cleanup kubelet startup ([#35319](https://github.com/kubernetes/kubernetes/pull/35319), [@vishh](https://github.com/vishh))
* Add a retry when reading a file content from a container ([#35560](https://github.com/kubernetes/kubernetes/pull/35560), [@jingxu97](https://github.com/jingxu97))