Add config to list the latest supported k8s versions from AKS via ter…

…raform

terraform/azure/cluster.tf

@@ -1,3 +1,24 @@
+# This data resource and output provides information on the latest available k8s
+# versions supported by Azure Kubernetes Service. This can be used when specifying
+# versions to upgrade to via the kubernetes_version variable.
+#
+# To get the output of relevance, run:
+#
+#     terraform plan -var-file=projects/$CLUSTER_NAME.tfvars
+#
+# ref: https://registry.terraform.io/providers/hashicorp/azurerm/latest/docs/data-sources/kubernetes_service_versions
+data "azurerm_kubernetes_service_versions" "k8s_version_prefixes" {
+  location = var.location
+
+  for_each       = var.k8s_version_prefixes
+  version_prefix = each.value
+}
+output "latest_supported_k8s_versions" {
+  value = { #data.azurerm_kubernetes_service_versions.current.versions
+    for k, v in data.azurerm_kubernetes_service_versions.k8s_version_prefixes: k => v.latest_version
+  }
+}
+
 # ref: https://registry.terraform.io/providers/hashicorp/azurerm/latest/docs/resources/kubernetes_cluster
 resource "azurerm_kubernetes_cluster" "jupyterhub" {
   name                = "hub-cluster"

terraform/azure/variables.tf

@@ -55,10 +55,20 @@ variable "kubernetes_version" {
   Version of kubernetes the cluster should use.
 
   `az aks get-versions --location westus2 -o table` will
-  display the list of available versions.
+  display the list of available versions. Or the terraform
+  output called latest_supported_k8s_versions if running against
+  an existing cluster.
   EOT
 }
 
+variable "k8s_version_prefixes" {
+  type = set(string)
+  default = [ "1.29", "1.30", "1." ]
+  description = <<-EOT
+  A list of k8s version prefixes that can be evaluated to their latest version by
+  the output defined in cluster.tf called latest_supported_k8s_versions.
+  EOT
+}
 
 variable "global_container_registry_name" {
   type        = string
@@ -188,4 +198,4 @@ variable "budget_alert_amount" {
   Amount of *forecasted spend* at which to send a billing alert. Current practice
   is to set this to the average of the last 3 months expenditure + 20%.
   EOT
-}
+}