* Controller preemption is not safe or covered in documentation. Delete
the option, the variable is a holdover from old experiments
* Note, worker_preemeptible is still a great feature that's supported
* Change Google Cloud module to require the `region` variable
* Workers are created in random zones within the given region
* Tolerate Google Cloud zone failures or capacity issues
* If workers are preempted (if enabled), replacement instances can
be drawn from any zone in the region, which should avoid scheduling
issues that were possible before if a single zone aggressively
preempts instances (presumably due to Google Cloud capacity)
* Kubernetes v1.8.2 fixes a memory leak in the v1.8.1 apiserver
* Switch to using the `gcr.io/google_containers/hyperkube` for the
on-host kubelet and shutdown drains
* Update terraform-render-bootkube manifests generation
* Update flannel from v0.8.0 to v0.9.0
* Add `hairpinMode` to flannel CNI config
* Add `--no-negcache` to kube-dns dnsmasq
* Terraform provider "google" plugin releases leave the disk
device_name as "" by default. Recently the API has started to
set a default name "persistent-disk-0". Plan and apply show
all instance groups need to be recreated to "fix" the name
* Impact: Controller and worker instance groups are deleted
and recreated, deleting data on controllers and bringing
down clusters
* Fix: Explicitly set the disk_name to persistent-disk-0 so
that terraform finds no diff needs to be applied.
* https://github.com/poseidon/typhoon/issues/34
* https://github.com/terraform-providers/terraform-provider-google/issues/574
* Calico on GCE with IP-in-IP encapsulation and MTU 1440
* Calico on DO with IP-in-IP encapsulation and MTU 1440
* Digital Ocean firewalls don't support IPIP protocol yet
* Remove k8s_domain_name input variable, the controller DNS
record will be "${var.cluster_name}.${dns_zone}"
* Rename dns_base_zone to dns_zone
* Rename dns_base_zone_name to dns_zone_name
