Remove the cluster_domain_suffix variable

* Drop support for `cluster_domain_suffix` customization and
always use `cluster.local`. Many components in the Kubernetes
ecosystem assume this default suffix and its very rare to be
setting a special value here these days
* Cleanup a few variables that are seldom used

azure/flatcar-linux/kubernetes/bootstrap.tf

@@ -14,7 +14,6 @@ module "bootstrap" {
 
   pod_cidr              = var.pod_cidr
   service_cidr          = var.service_cidr
-  cluster_domain_suffix = var.cluster_domain_suffix
   enable_reporting      = var.enable_reporting
   enable_aggregation    = var.enable_aggregation
   daemonset_tolerations = var.daemonset_tolerations

azure/flatcar-linux/kubernetes/butane/controller.yaml

@@ -144,7 +144,7 @@ storage:
           cgroupDriver: systemd
           clusterDNS:
             - ${cluster_dns_service_ip}
-          clusterDomain: ${cluster_domain_suffix}
+          clusterDomain: cluster.local
           healthzPort: 0
           rotateCertificates: true
           shutdownGracePeriod: 45s

azure/flatcar-linux/kubernetes/controllers.tf

@@ -185,7 +185,6 @@ data "ct_config" "controllers" {
     kubeconfig             = indent(10, module.bootstrap.kubeconfig-kubelet)
     ssh_authorized_key     = var.ssh_authorized_key
     cluster_dns_service_ip = cidrhost(var.service_cidr, 10)
-    cluster_domain_suffix  = var.cluster_domain_suffix
   })
   strict   = true
   snippets = var.controller_snippets

azure/flatcar-linux/kubernetes/variables.tf

@@ -196,14 +196,6 @@ variable "daemonset_tolerations" {
   default     = []
 }
 
-# unofficial, undocumented, unsupported
-
-variable "cluster_domain_suffix" {
-  type        = string
-  description = "Queries for domains with the suffix will be answered by coredns. Default is cluster.local (e.g. foo.default.svc.cluster.local) "
-  default     = "cluster.local"
-}
-
 variable "components" {
   description = "Configure pre-installed cluster components"
   # Component configs are passed through to terraform-render-bootstrap,

azure/flatcar-linux/kubernetes/workers.tf

@@ -18,12 +18,11 @@ module "workers" {
   priority       = var.worker_priority
 
   # configuration
-  kubeconfig            = module.bootstrap.kubeconfig-kubelet
-  ssh_authorized_key    = var.ssh_authorized_key
-  azure_authorized_key  = var.azure_authorized_key
-  service_cidr          = var.service_cidr
-  cluster_domain_suffix = var.cluster_domain_suffix
-  snippets              = var.worker_snippets
-  node_labels           = var.worker_node_labels
-  arch                  = var.worker_arch
+  kubeconfig           = module.bootstrap.kubeconfig-kubelet
+  ssh_authorized_key   = var.ssh_authorized_key
+  azure_authorized_key = var.azure_authorized_key
+  service_cidr         = var.service_cidr
+  snippets             = var.worker_snippets
+  node_labels          = var.worker_node_labels
+  arch                 = var.worker_arch
 }

azure/flatcar-linux/kubernetes/workers/butane/worker.yaml

@@ -99,7 +99,7 @@ storage:
           cgroupDriver: systemd
           clusterDNS:
             - ${cluster_dns_service_ip}
-          clusterDomain: ${cluster_domain_suffix}
+          clusterDomain: cluster.local
           healthzPort: 0
           rotateCertificates: true
           shutdownGracePeriod: 45s

azure/flatcar-linux/kubernetes/workers/variables.tf

@@ -137,12 +137,3 @@ variable "arch" {
     error_message = "The arch must be amd64 or arm64."
   }
 }
-
-# unofficial, undocumented, unsupported
-
-variable "cluster_domain_suffix" {
-  description = "Queries for domains with the suffix will be answered by coredns. Default is cluster.local (e.g. foo.default.svc.cluster.local) "
-  type        = string
-  default     = "cluster.local"
-}
-

azure/flatcar-linux/kubernetes/workers/workers.tf

@@ -105,7 +105,6 @@ data "ct_config" "worker" {
     kubeconfig             = indent(10, var.kubeconfig)
     ssh_authorized_key     = var.ssh_authorized_key
     cluster_dns_service_ip = cidrhost(var.service_cidr, 10)
-    cluster_domain_suffix  = var.cluster_domain_suffix
     node_labels            = join(",", var.node_labels)
     node_taints            = join(",", var.node_taints)
   })