aws_rds_cluster: Fix Regression in serverlessv2_scaling_configuration Handling

.changelog/40511.txt

@@ -0,0 +1,3 @@
+```release-note:bug
+resource/aws_rds_cluster: Fix `InvalidParameterValue: Serverless v2 maximum capacity 0.0 isn't valid. The maximum capacity must be at least 1.0.` errors when removing `serverlessv2_scaling_configuration` in an update
+```

internal/service/rds/cluster.go

@@ -547,7 +547,22 @@ func resourceCluster() *schema.Resource {
 						names.AttrMaxCapacity: {
 							Type:         schema.TypeFloat,
 							Required:     true,
-							ValidateFunc: validation.FloatBetween(0, 256),
+							ValidateFunc: validation.FloatBetween(1, 256),
+							DiffSuppressFunc: func(k, old, new string, d *schema.ResourceData) bool {
+								// Handles a breaking regression. On v5.79.0 and earlier,
+								// serverlessv2_scaling_configuration block could be removed from
+								// configuration. Although doing so doesn't actually remove the scaling
+								// configuration from AWS this dsf does allow the user to remove the block
+								// from their configuration without perpetual diffs.
+								// https://github.com/hashicorp/terraform-provider-aws/issues/40473
+								config := d.GetRawConfig()
+								raw := config.GetAttr("serverlessv2_scaling_configuration")
+
+								if raw.LengthInt() == 0 && (old != "0" && old != "") && (new == "0" || new == "") {
+									return true
+								}
+								return false
+							},
 						},
 						"min_capacity": {
 							Type:         schema.TypeFloat,
@@ -2164,7 +2179,9 @@ func expandServerlessV2ScalingConfiguration(tfMap map[string]interface{}) *types
 
 	apiObject := &types.ServerlessV2ScalingConfiguration{}
 
-	if v, ok := tfMap[names.AttrMaxCapacity].(float64); ok {
+	// Removing the serverlessv2_scaling_configuration block from config for an update, sets max_capacity
+	// to 0. Sending 0 to the API causes an error.
+	if v, ok := tfMap[names.AttrMaxCapacity].(float64); ok && v != 0.0 {
 		apiObject.MaxCapacity = aws.Float64(v)
 	}
 

internal/service/rds/cluster_test.go

@@ -2123,6 +2123,43 @@ func TestAccRDSCluster_serverlessV2ScalingConfiguration(t *testing.T) {
 	})
 }
 
+func TestAccRDSCluster_serverlessV2ScalingRemoved(t *testing.T) {
+	ctx := acctest.Context(t)
+	if testing.Short() {
+		t.Skip("skipping long-running test in short mode")
+	}
+
+	var dbCluster types.DBCluster
+
+	rName := sdkacctest.RandomWithPrefix(acctest.ResourcePrefix)
+	resourceName := "aws_rds_cluster.test"
+
+	resource.ParallelTest(t, resource.TestCase{
+		PreCheck:                 func() { acctest.PreCheck(ctx, t) },
+		ErrorCheck:               acctest.ErrorCheck(t, names.RDSServiceID),
+		ProtoV5ProviderFactories: acctest.ProtoV5ProviderFactories,
+		CheckDestroy:             testAccCheckClusterDestroy(ctx),
+		Steps: []resource.TestStep{
+			{
+				Config: testAccClusterConfig_serverlessV2ScalingConfiguration(rName, 64.0, 2.5),
+				Check: resource.ComposeTestCheckFunc(
+					testAccCheckClusterExists(ctx, resourceName, &dbCluster),
+					resource.TestCheckResourceAttr(resourceName, "serverlessv2_scaling_configuration.#", "1"),
+					resource.TestCheckResourceAttr(resourceName, "serverlessv2_scaling_configuration.0.max_capacity", "64"),
+					resource.TestCheckResourceAttr(resourceName, "serverlessv2_scaling_configuration.0.min_capacity", "2.5"),
+					resource.TestCheckResourceAttrSet(resourceName, "serverlessv2_scaling_configuration.0.seconds_until_auto_pause"),
+				),
+			},
+			{
+				Config: testAccClusterConfig_serverlessV2ScalingRemoved(rName),
+				Check: resource.ComposeTestCheckFunc(
+					testAccCheckClusterExists(ctx, resourceName, &dbCluster),
+				),
+			},
+		},
+	})
+}
+
 // Reference: https://github.com/hashicorp/terraform-provider-aws/issues/11698
 func TestAccRDSCluster_Scaling_defaultMinCapacity(t *testing.T) {
 	ctx := acctest.Context(t)
@@ -5244,6 +5281,25 @@ resource "aws_rds_cluster" "test" {
 `, tfrds.ClusterEngineAuroraPostgreSQL, rName, maxCapacity, minCapacity)
 }
 
+func testAccClusterConfig_serverlessV2ScalingRemoved(rName string) string {
+	return fmt.Sprintf(`
+data "aws_rds_orderable_db_instance" "test" {
+  engine                     = %[1]q
+  engine_latest_version      = true
+  preferred_instance_classes = ["db.serverless"]
+}
+
+resource "aws_rds_cluster" "test" {
+  cluster_identifier  = %[2]q
+  master_password     = "avoid-plaintext-passwords"
+  master_username     = "tfacctest"
+  skip_final_snapshot = true
+  engine              = data.aws_rds_orderable_db_instance.test.engine
+  engine_version      = data.aws_rds_orderable_db_instance.test.engine_version
+}
+`, tfrds.ClusterEngineAuroraPostgreSQL, rName)
+}
+
 func testAccClusterConfig_serverlessV2ScalingConfigurationWithSecondsUntilAutoPause(rName string, maxCapacity, minCapacity float64, secondsUntilAutoPause int) string {
 	return fmt.Sprintf(`
 data "aws_rds_orderable_db_instance" "test" {