Notable changes between versions.

• Kubernetes v1.7.5
• Use kubernete-incubator/bootkube v0.6.2
• Add AWS Terraform module (alpha)
• Add support for Calico networking (bare-metal, Google Cloud, AWS)
• Change networking default from "flannel" to "calico"

• Add network_mtu to allow CNI interface MTU customization

• Add network_mtu to allow CNI interface MTU customization
• Remove support for experimental_self_hosted_etcd

• Kubernetes v1.7.3
• Use kubernete-incubator/bootkube v0.6.1

• Add cloud firewall rules (requires Terraform v0.10)
• Change nodes tags from strings to DO tags

• Kubernetes v1.7.1
• Use kubernete-incubator/bootkube v0.6.0
• Add Bare-Metal Terraform module (stable)
• Add Digital Ocean Terraform module (beta)

• Remove k8s_domain_name variable, cluster_name + dns_zone resolves to controllers
• Rename dns_base_zone to dns_zone
• Rename dns_base_zone_name to dns_zone_name

• Kubernetes v1.6.7
• Use kubernete-incubator/bootkube v0.5.1

• Kubernetes v1.6.6
• Use kubernete-incubator/bootkube v0.4.5
• Disable locksmithd on hosts, in favor of CLUO.

• Kubernetes v1.6.4
• Add Google Cloud Terraform module (stable)

Earlier versions, back to v1.3.0, used different designs and mechanisms.