error if it is not available.  Clients may request fallback to the normal object by adding a non-qualified mime-type to their `Accept` header like `application/json` - the server will then respond with either the alternate representation if it is supported or the fallback mime-type which is the normal object response. ([#59059](https://github.com/kubernetes/kubernetes/pull/59059), [@smarterclayton](https://github.com/smarterclayton))

* kube-apiserver now uses SSH tunnels for webhooks if...

- Resolves a spurious "Unknown discovery response content-type" error in client-go discovery requests by tolerating extra content-type parameters in API responses ([#117637](https://github.com/kubernetes/kubernetes/pull/117637), [@seans3](https://github.com/seans3)) [SIG API Machinery]

* Correct wording of kubeadm upgrade response for missing ConfigMap. ([#53337](https://github.com/kubernetes/kubernetes/pull/53337), [@jmhardison](https://github.com/jmhardison))

- The `export` query parameter (inconsistently supported by API resources and deprecated in v1.14) is fully removed.  Requests setting this query parameter will now receive a 400 status response. ([#98312](https://github.com/kubernetes/kubernetes/pull/98312), [@deads2k](https://github.com/deads2k)) [SIG API Machinery, Auth and Testing]

  The API Server will no longer proxy non-101 responses for upgrade requests. This could break proxied backends (such as an extension API server) that respond to upgrade requests with a non-101 response code. ([#92941](https://github.com/kubernetes/kubernetes/pull/92941), [@tallclair](https://github.com/tallclair)) [SIG API Machinery]
 
## Changes by Kind

### API Change

- Kube-proxy service health returns http header `X-Load-Balancing-Endpoint-Weight` with number of local endpoints. The same information is still available in response body JSON `payload.LocalEndpoints`. ([#118999](https://github.com/kubernetes/kubernetes/pull/118999), [@cezarygerard](https://github.com/cezarygerard))

For more information and for updates on resolution of this issue, see [#51899](https://github.com/kubernetes/kubernetes/issues/51899).

* Add "only_cpu_and_memory" GET parameter to /stats/summary http handler in kubelet. If parameter is true then only cpu and memory will be present in response. ([#67829](https://github.com/kubernetes/kubernetes/pull/67829), [@krzysztof-jastrzebski](https://github.com/krzysztof-jastrzebski))

  The API Server will no longer proxy non-101 responses for upgrade requests. This could break proxied backends (such as an extension API server) that respond to upgrade requests with a non-101 response code. ([#92941](https://github.com/kubernetes/kubernetes/pull/92941), [@tallclair](https://github.com/tallclair)) [SIG API Machinery]

  The API Server will no longer proxy non-101 responses for upgrade requests. This could break proxied backends (such as an extension API server) that respond to upgrade requests with a non-101 response code. ([#92941](https://github.com/kubernetes/kubernetes/pull/92941), [@tallclair](https://github.com/tallclair)) [SIG API Machinery]
 
## Changes by Kind

### Deprecation