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

aws/flatcar-linux/kubernetes/bootstrap.tf

@@ -9,7 +9,6 @@ module "bootstrap" {
   network_mtu           = var.network_mtu
   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

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

@@ -148,7 +148,7 @@ storage:
           cgroupDriver: systemd
           clusterDNS:
             - ${cluster_dns_service_ip}
-          clusterDomain: ${cluster_domain_suffix}
+          clusterDomain: cluster.local
           healthzPort: 0
           rotateCertificates: true
           shutdownGracePeriod: 45s

aws/flatcar-linux/kubernetes/controllers.tf

@@ -66,7 +66,6 @@ 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

aws/flatcar-linux/kubernetes/variables.tf

@@ -164,6 +164,14 @@ EOD
   default     = "10.3.0.0/16"
 }
 
+variable "worker_node_labels" {
+  type        = list(string)
+  description = "List of initial worker node labels"
+  default     = []
+}
+
+# advanced
+
 variable "enable_reporting" {
   type        = bool
   description = "Enable usage or analytics reporting to upstreams (Calico)"
@@ -176,20 +184,6 @@ variable "enable_aggregation" {
   default     = true
 }
 
-variable "worker_node_labels" {
-  type        = list(string)
-  description = "List of initial worker node labels"
-  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 "controller_arch" {
   type        = string
   description = "Controller node(s) architecture (amd64 or arm64)"
@@ -210,7 +204,6 @@ variable "worker_arch" {
   }
 }
 
-
 variable "daemonset_tolerations" {
   type        = list(string)
   description = "List of additional taint keys kube-system DaemonSets should tolerate (e.g. ['custom-role', 'gpu-role'])"

aws/flatcar-linux/kubernetes/workers.tf

@@ -6,22 +6,23 @@ module "workers" {
   vpc_id          = aws_vpc.network.id
   subnet_ids      = aws_subnet.public.*.id
   security_groups = [aws_security_group.worker.id]
-  worker_count    = var.worker_count
-  instance_type   = var.worker_type
-  os_image        = var.os_image
-  arch            = var.worker_arch
-  disk_type       = var.worker_disk_type
-  disk_size       = var.worker_disk_size
-  disk_iops       = var.worker_disk_iops
-  spot_price      = var.worker_price
-  target_groups   = var.worker_target_groups
+
+  # instances
+  os_image      = var.os_image
+  worker_count  = var.worker_count
+  instance_type = var.worker_type
+  arch          = var.worker_arch
+  disk_type     = var.worker_disk_type
+  disk_size     = var.worker_disk_size
+  disk_iops     = var.worker_disk_iops
+  spot_price    = var.worker_price
+  target_groups = var.worker_target_groups
 
   # 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
-  snippets              = var.worker_snippets
-  node_labels           = var.worker_node_labels
+  kubeconfig         = module.bootstrap.kubeconfig-kubelet
+  ssh_authorized_key = var.ssh_authorized_key
+  service_cidr       = var.service_cidr
+  snippets           = var.worker_snippets
+  node_labels        = var.worker_node_labels
 }
 

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

@@ -103,7 +103,7 @@ storage:
           cgroupDriver: systemd
           clusterDNS:
             - ${cluster_dns_service_ip}
-          clusterDomain: ${cluster_domain_suffix}
+          clusterDomain: cluster.local
           healthzPort: 0
           rotateCertificates: true
           shutdownGracePeriod: 45s

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

@@ -108,12 +108,6 @@ 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"
-}
-
 variable "node_labels" {
   type        = list(string)
   description = "List of initial node labels"
@@ -134,7 +128,7 @@ variable "arch" {
   default     = "amd64"
 
   validation {
-    condition     = var.arch == "amd64" || var.arch == "arm64"
+    condition     = contains(["amd64", "arm64"], var.arch)
     error_message = "The arch must be amd64 or arm64."
   }
 }

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

@@ -111,7 +111,6 @@ 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)
   })