Add optional cluster_domain_suffix variable

* Allow kube-dns to respond to DNS queries with a custom
suffix, instead of the default 'cluster.local'
* Useful when multiple clusters exist on the same local
network and wish to query services on one another

google-cloud/container-linux/kubernetes/controllers/cl/controller.yaml.tmpl

@@ -74,7 +74,7 @@ systemd:
           --anonymous-auth=false \
           --client-ca-file=/etc/kubernetes/ca.crt \
           --cluster_dns=${k8s_dns_service_ip} \
-          --cluster_domain=cluster.local \
+          --cluster_domain=${cluster_domain_suffix} \
           --cni-conf-dir=/etc/kubernetes/cni/net.d \
           --exit-on-lock-contention \
           --kubeconfig=/etc/kubernetes/kubeconfig \

google-cloud/container-linux/kubernetes/controllers/controllers.tf

@@ -66,6 +66,7 @@ data "template_file" "controller_config" {
     etcd_initial_cluster = "${join(",", formatlist("%s=https://%s:2380", null_resource.repeat.*.triggers.name, null_resource.repeat.*.triggers.domain))}"
 
     k8s_dns_service_ip      = "${cidrhost(var.service_cidr, 10)}"
+    cluster_domain_suffix   = "${var.cluster_domain_suffix}"
     ssh_authorized_key      = "${var.ssh_authorized_key}"
     kubeconfig_ca_cert      = "${var.kubeconfig_ca_cert}"
     kubeconfig_kubelet_cert = "${var.kubeconfig_kubelet_cert}"

google-cloud/container-linux/kubernetes/controllers/variables.tf

@@ -69,6 +69,12 @@ EOD
   default = "10.3.0.0/16"
 }
 
+variable "cluster_domain_suffix" {
+  description = "Queries for domains with the suffix will be answered by kube-dns. Default is cluster.local (e.g. foo.default.svc.cluster.local) "
+  type        = "string"
+  default     = "cluster.local"
+}
+
 // kubeconfig
 
 variable "kubeconfig_ca_cert" {