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

bare-metal/flatcar-linux/kubernetes/bootstrap.tf

@@ -10,7 +10,6 @@ module "bootstrap" {
   network_ip_autodetection_method = var.network_ip_autodetection_method
   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
   components                      = var.components

bare-metal/flatcar-linux/kubernetes/butane/controller.yaml

@@ -155,7 +155,7 @@ storage:
           cgroupDriver: systemd
           clusterDNS:
             - ${cluster_dns_service_ip}
-          clusterDomain: ${cluster_domain_suffix}
+          clusterDomain: cluster.local
           healthzPort: 0
           rotateCertificates: true
           shutdownGracePeriod: 45s

bare-metal/flatcar-linux/kubernetes/profiles.tf

@@ -88,7 +88,6 @@ data "ct_config" "controllers" {
     etcd_name              = var.controllers.*.name[count.index]
     etcd_initial_cluster   = join(",", formatlist("%s=https://%s:2380", var.controllers.*.name, var.controllers.*.domain))
     cluster_dns_service_ip = module.bootstrap.cluster_dns_service_ip
-    cluster_domain_suffix  = var.cluster_domain_suffix
     ssh_authorized_key     = var.ssh_authorized_key
   })
   strict   = true

bare-metal/flatcar-linux/kubernetes/variables.tf

@@ -167,13 +167,7 @@ EOD
   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"
-}
+# advanced
 
 variable "components" {
   description = "Configure pre-installed cluster components"

bare-metal/flatcar-linux/kubernetes/worker/butane/worker.yaml

@@ -113,7 +113,7 @@ storage:
           cgroupDriver: systemd
           clusterDNS:
             - ${cluster_dns_service_ip}
-          clusterDomain: ${cluster_domain_suffix}
+          clusterDomain: cluster.local
           healthzPort: 0
           rotateCertificates: true
           shutdownGracePeriod: 45s

bare-metal/flatcar-linux/kubernetes/worker/matchbox.tf

@@ -79,7 +79,6 @@ data "ct_config" "worker" {
     domain_name            = var.domain
     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)
   })

bare-metal/flatcar-linux/kubernetes/worker/variables.tf

@@ -114,13 +114,3 @@ The 1st IP will be reserved for kube_apiserver, the 10th IP will be reserved for
 EOD
   default     = "10.3.0.0/16"
 }
-
-
-
-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"
-}
-
-

bare-metal/flatcar-linux/kubernetes/workers.tf

@@ -15,13 +15,12 @@ module "workers" {
   domain = var.workers[count.index].domain
 
   # configuration
-  kubeconfig            = module.bootstrap.kubeconfig-kubelet
-  ssh_authorized_key    = var.ssh_authorized_key
-  service_cidr          = var.service_cidr
-  cluster_domain_suffix = var.cluster_domain_suffix
-  node_labels           = lookup(var.worker_node_labels, var.workers[count.index].name, [])
-  node_taints           = lookup(var.worker_node_taints, var.workers[count.index].name, [])
-  snippets              = lookup(var.snippets, var.workers[count.index].name, [])
+  kubeconfig         = module.bootstrap.kubeconfig-kubelet
+  ssh_authorized_key = var.ssh_authorized_key
+  service_cidr       = var.service_cidr
+  node_labels        = lookup(var.worker_node_labels, var.workers[count.index].name, [])
+  node_taints        = lookup(var.worker_node_taints, var.workers[count.index].name, [])
+  snippets           = lookup(var.snippets, var.workers[count.index].name, [])
 
   # optional
   download_protocol = var.download_protocol