[@kawych](https://github.com/kawych))

* On cluster provision or upgrade, kubeadm now generates certs and secures all connections to the etcd static-pod with mTLS. This includes the etcd serving cert, the etcd peer cert, and the apiserver etcd client cert. Flags and hostMounts are added to the etcd and apiserver static-pods to load these certs. For connections to etcd, https is now used in favor of http. ([#57415](https://github.com/kubernetes/kubernetes/pull/57415), [@stealthybox](htt...

by default). An API server fronted by an L7 load balancer that already mitigates these http/2 attacks may choose not to enable the kube-apiserver mitigation to avoid disrupting load balancer → kube-apiserver connections if http/2 requests from multiple clients share the same backend connection. An API server on a private network may choose not to enable the kube-apiserver mitigation to prevent performance regressions for unauthenticated clients. Authenticated requests rely on the fix in golang.org/x/net...

#### **Audit**

*   Fixed a bug so that `kube-apiserver` now waits for open connections to finish before exiting. This fix provides graceful shutdown and ensures that the audit backend no longer drops events on shutdown. ([#53695](https://github.com/kubernetes/kubernetes/pull/53695),[ @hzxuzhonghu](https://github.com/hzxuzhonghu))

* After a kubelet rotates its client cert, it now closes its connections to the API server to force a handshake using the new cert. Previously, the kubelet could keep its existing connection open, even if the cert used for that connection was expired and rejected by the API server. ([#49899](https://github.com/kubernetes/kubernetes/pull/49899), [@ericchiang](https://github.com/ericchiang))

- Kube-proxy: fix a bug on UDP `NodePort` Services where stale connection tracking entries may blackhole the traffic directed to the `NodePort` ([#98305](https://github.com/kubernetes/kubernetes/pull/98305), [@aojea](https://github.com/aojea))

- HTTP/2 connection health check is enabled by default in all Kubernetes clients to fix persistently broken connections (https://github.com/kubernetes/client-go/issues/374). If needed, users can tune the feature via the HTTP2_READ_IDLE_TIMEOUT_SECONDS and HTTP2_PING_TIMEOUT_SECONDS environment variables. The feature...

by default). An API server fronted by an L7 load balancer that already mitigates these http/2 attacks may choose not to enable the kube-apiserver mitigation to avoid disrupting load balancer → kube-apiserver connections if http/2 requests from multiple clients share the same backend connection. An API server on a private network may choose not to enable the kube-apiserver mitigation to prevent performance regressions for unauthenticated clients. Authenticated requests rely on the fix in golang.org/x/net...

## Changelog since v1.13.5

### Other notable changes

* Connections from Pods to Services with 0 endpoints will now ICMP reject immediately, rather than blackhole and timeout. ([#72534](https://github.com/kubernetes/kubernetes/pull/72534), [@thockin](https://github.com/thockin))

by default). An API server fronted by an L7 load balancer that already mitigates these http/2 attacks may choose not to enable the kube-apiserver mitigation to avoid disrupting load balancer → kube-apiserver connections if http/2 requests from multiple clients share the same backend connection. An API server on a private network may choose not to enable the kube-apiserver mitigation to prevent performance regressions for unauthenticated clients. Authenticated requests rely on the fix in golang.org/x/net...

- The kubelet no longer forcefully closes active connections on heartbeat failures, using the HTTP2 health check mechanism to detect broken connections. Users can force the previous behavior of the kubelet by setting the environment variable DISABLE_HTTP2. ([#108107](https://github.com/kubernetes/kubernetes/pull/108107), [@aojea](https://github.com/aojea))...