Allow updating DNSConfig in-place (#9446) (#16652)

* Allow updating DNSConfig in-place

* leave DNS_SCOPE_UNSPECIFIED as default for cluster_dns_scope

* Revert expandDnsConfig() return change

* Add DNSConfig update test step
[upstream:95bc4cc1c10e7ed012f9f67eb2e876d796cdf30d]

Signed-off-by: Modular Magician <[email protected]>

Author: modular-magician

.changelog/9446.txt

@@ -0,0 +1,3 @@
+```release-note:bug
+Allow updating DNSConfig in-place
+```

google/services/container/resource_container_cluster.go

@@ -1794,7 +1794,6 @@ func ResourceContainerCluster() *schema.Resource {
 				Type:             schema.TypeList,
 				Optional:         true,
 				MaxItems:         1,
-				ForceNew:         true,
 				DiffSuppressFunc: suppressDiffForAutopilot,
 				Description:      `Configuration for Cloud DNS for Kubernetes Engine.`,
 				Elem: &schema.Resource{
@@ -2702,6 +2701,22 @@ func resourceContainerClusterUpdate(d *schema.ResourceData, meta interface{}) er
 		log.Printf("[INFO] GKE cluster %s's cluster-wide autoscaling has been updated", d.Id())
 	}
 
+	if d.HasChange("dns_config") {
+		req := &container.UpdateClusterRequest{
+			Update: &container.ClusterUpdate{
+				DesiredDnsConfig: expandDnsConfig(d.Get("dns_config")),
+			},
+		}
+
+		updateF := updateFunc(req, "updating GKE cluster DNSConfig")
+		// Call update serially.
+		if err := transport_tpg.LockedCall(lockKey, updateF); err != nil {
+			return err
+		}
+
+		log.Printf("[INFO] GKE cluster %s's DNSConfig has been updated", d.Id())
+	}
+
 	if d.HasChange("allow_net_admin") {
 		allowed := d.Get("allow_net_admin").(bool)
 		req := &container.UpdateClusterRequest{

google/services/container/resource_container_cluster_migratev1.go

@@ -1595,7 +1595,6 @@ func resourceContainerClusterResourceV1() *schema.Resource {
 				Type:             schema.TypeList,
 				Optional:         true,
 				MaxItems:         1,
-				ForceNew:         true,
 				DiffSuppressFunc: suppressDiffForAutopilot,
 				Description:      `Configuration for Cloud DNS for Kubernetes Engine.`,
 				Elem: &schema.Resource{

google/services/container/resource_container_cluster_test.go

@@ -3485,11 +3485,20 @@ func TestAccContainerCluster_withDNSConfig(t *testing.T) {
 		ProtoV5ProviderFactories: acctest.ProtoV5ProviderFactories(t),
 		CheckDestroy:             testAccCheckContainerClusterDestroyProducer(t),
 		Steps: []resource.TestStep{
+			{
+				Config: testAccContainerCluster_basic(clusterName, networkName, subnetworkName),
+			},
+			{
+				ResourceName:            "google_container_cluster.primary",
+				ImportState:             true,
+				ImportStateVerify:       true,
+				ImportStateVerifyIgnore: []string{"deletion_protection"},
+			},
 			{
 				Config: testAccContainerCluster_withDNSConfig(clusterName, "CLOUD_DNS", domainName, "VPC_SCOPE", networkName, subnetworkName),
 			},
 			{
-				ResourceName:            "google_container_cluster.with_dns_config",
+				ResourceName:            "google_container_cluster.primary",
 				ImportState:             true,
 				ImportStateVerify:       true,
 				ImportStateVerifyIgnore: []string{"deletion_protection"},
@@ -7314,9 +7323,9 @@ resource "google_container_cluster" "with_autopilot" {
 
 func testAccContainerCluster_withDNSConfig(clusterName, clusterDns, clusterDnsDomain, clusterDnsScope, networkName, subnetworkName string) string {
 	return fmt.Sprintf(`
-resource "google_container_cluster" "with_dns_config" {
-  name               = "%s"
-  location           = "us-central1-f"
+resource "google_container_cluster" "primary" {
+	name               = "%s"
+	location           = "us-central1-a"
   initial_node_count = 1
   dns_config {
     cluster_dns 	   = "%s"