allow configuration of kubernetes version (#18)

* allow configuration of kubernetes version

* update tf init to use a different key for each test

* allow partial kubernetes versions

.circleci/config.yml

@@ -37,7 +37,7 @@ jobs:
 
       - run:
           name: Terraform init
-          command: terraform init
+          command: terraform init -backend-config=key=$WORKSPACE.tfstate
 
       - run:
           name: Terraform validate

aks.tf

@@ -5,6 +5,12 @@ locals {
   }
 }
 
+data "azurerm_kubernetes_service_versions" "selected" {
+  location        = local.resource_group.location
+  version_prefix  = var.kubernetes_version
+  include_preview = false
+}
+
 resource "azurerm_kubernetes_cluster" "aks" {
   lifecycle {
     ignore_changes = [
@@ -23,6 +29,7 @@ resource "azurerm_kubernetes_cluster" "aks" {
   dns_prefix              = local.cluster_name
   private_cluster_enabled = false
   sku_tier                = var.cluster_sku_tier
+  kubernetes_version      = var.kubernetes_version != null ? data.azurerm_kubernetes_service_versions.selected.latest_version : null
 
   api_server_authorized_ip_ranges = var.api_server_authorized_ip_ranges
 

variables.tf

@@ -143,3 +143,9 @@ variable "tags" {
   default     = {}
   description = "Tags to apply to resources"
 }
+
+variable "kubernetes_version" {
+  type        = string
+  default     = null
+  description = "Optional Kubernetes version to provision. Allows partial input (e.g. 1.18) which is then chosen from azurerm_kubernetes_service_versions."
+}