* Fix GCE etcd scripts to pass in all required parameters for the etcd migration utility to correctly perform HA upgrades and downgrades ([#61957](https://github.com/kubernetes/kubernetes/pull/61957), [@jpbetz](https://github.com/jpbetz))

  - Renew certs as part of upgrade.
  - New `kubeadm alpha phase certs renew` command for renewing certificates.
  - Certificates created with kubeadm now have improved uniqueness of Distinguished Name fields.
- HA improvements:
  - `kubeadm join --experimental-control-plane` can now be used to join control plane instances to an existing cluster.

* corrects a race condition in bootstrapping aggregated cluster roles in new HA clusters ([#63761](https://github.com/kubernetes/kubernetes/pull/63761), [@liggitt](https://github.com/liggitt))

* corrects a race condition in bootstrapping aggregated cluster roles in new HA clusters ([#63761](https://github.com/kubernetes/kubernetes/pull/63761), [@liggitt](https://github.com/liggitt))

- Ensure empty string annotations are copied over in rollbacks. ([#94858](https://github.com/kubernetes/kubernetes/pull/94858), [@waynepeking348](https://github.com/waynepeking348))
- Ensure only one LoadBalancer rule is created when HA mode is enabled ([#99825](https://github.com/kubernetes/kubernetes/pull/99825), [@feiskyer](https://github.com/feiskyer)) [SIG Cloud Provider]

* Added Establishing Controller on CRDs to avoid race between Established condition and CRs actually served. In HA setups, the Established condition is delayed by 5 seconds. ([#63068](https://github.com/kubernetes/kubernetes/pull/63068), [@xmudrii](https://github.com/xmudrii))

* kubeadm: fix a possible panic when joining a new control plane node in HA scenarios ([#72123](https://github.com/kubernetes/kubernetes/pull/72123), [@anitgandhi](https://github.com/anitgandhi))

Kubeadm: Automate certificate copy between control planes in HA setups

- Joining control plane nodes to a HA cluster can now be simplified by enabling the optional automatic copy of certificates from an existing control plane node.

* Fix a bug where soft eviction would not trigger when the threshold was crossed ([#52046](https://github.com/kubernetes/kubernetes/pull/52046), [@dashpole](https://github.com/dashpole))
* Addon manager supports HA masters. ([#55782](https://github.com/kubernetes/kubernetes/pull/55782), [@x13n](https://github.com/x13n))

1.6 encourages etcd3, and switching from etcd2 to etcd3 involves a full
migration of data between different storage engines.  You must stop the API
from writing to etcd during an etcd2 -> etcd3 migration.  HA installations cannot
be migrated at the current time using the official Kubernetes procedure.

1.6 will also default to protobuf encoding if using etcd3.  **This change is