azurerm_postgresql_flexible_server - move the error check for storage_mb from CustomizeDiff to Create/Update func

internal/services/postgres/postgresql_flexible_server_resource.go

@@ -384,11 +384,6 @@ func resourcePostgresqlFlexibleServer() *pluginsdk.Resource {
 			newMb = newStorageMbRaw.(int)
 			newTier = newTierRaw.(string)
 
-			// storage_mb can only be scaled up...
-			if newMb < oldStorageMbRaw.(int) {
-				return fmt.Errorf("'storage_mb' can only be scaled up, expected the new 'storage_mb' value (%d) to be larger than the previous 'storage_mb' value (%d)", newMb, oldStorageMbRaw.(int))
-			}
-
 			// if newMb or newTier values are empty,
 			// assign the default values that will
 			// be assigned in the create func...
@@ -517,7 +512,10 @@ func resourcePostgresqlFlexibleServerCreate(d *pluginsdk.ResourceData, meta inte
 		return fmt.Errorf("expanding `sku_name` for %s: %v", id, err)
 	}
 
-	storage := expandArmServerStorage(d)
+	storage, err := expandArmServerStorage(d)
+	if err != nil {
+		return err
+	}
 	var storageMb int
 
 	if storage.StorageSizeGB == nil || *storage.StorageSizeGB == 0 {
@@ -854,9 +852,14 @@ func resourcePostgresqlFlexibleServerUpdate(d *pluginsdk.ResourceData, meta inte
 
 	if d.HasChange("auto_grow_enabled") || d.HasChange("storage_mb") || d.HasChange("storage_tier") {
 		// TODO remove the additional update after https://github.com/Azure/azure-rest-api-specs/issues/22867 is fixed
+		storage, err := expandArmServerStorage(d)
+		if err != nil {
+			return err
+		}
+
 		storageUpdateParameters := servers.ServerForUpdate{
 			Properties: &servers.ServerPropertiesForUpdate{
-				Storage: expandArmServerStorage(d),
+				Storage: storage,
 			},
 		}
 
@@ -999,7 +1002,7 @@ func expandArmServerMaintenanceWindow(input []interface{}) *servers.MaintenanceW
 	return &maintenanceWindow
 }
 
-func expandArmServerStorage(d *pluginsdk.ResourceData) *servers.Storage {
+func expandArmServerStorage(d *pluginsdk.ResourceData) (*servers.Storage, error) {
 	storage := servers.Storage{}
 
 	autoGrow := servers.StorageAutoGrowDisabled
@@ -1008,6 +1011,12 @@ func expandArmServerStorage(d *pluginsdk.ResourceData) *servers.Storage {
 	}
 	storage.AutoGrow = &autoGrow
 
+	// storage_mb can only be scaled up...
+	oldStorageMbRaw, newStorageMbRaw := d.GetChange("storage_mb")
+	if newStorageMbRaw.(int) < oldStorageMbRaw.(int) {
+		return nil, fmt.Errorf("'storage_mb' can only be scaled up, expected the new 'storage_mb' value (%d) to be larger than the previous 'storage_mb' value (%d)", newStorageMbRaw.(int), oldStorageMbRaw.(int))
+	}
+
 	if v, ok := d.GetOk("storage_mb"); ok {
 		storage.StorageSizeGB = pointer.FromInt64(int64(v.(int) / 1024))
 	}
@@ -1016,7 +1025,7 @@ func expandArmServerStorage(d *pluginsdk.ResourceData) *servers.Storage {
 		storage.Tier = pointer.To(servers.AzureManagedDiskPerformanceTiers(v.(string)))
 	}
 
-	return &storage
+	return &storage, nil
 }
 
 func expandArmServerBackup(d *pluginsdk.ResourceData) *servers.Backup {

internal/services/postgres/postgresql_flexible_server_resource_test.go

@@ -583,6 +583,28 @@ func TestAccPostgresqlFlexibleServer_updateOnlyWithStorageTier(t *testing.T) {
 	})
 }
 
+func TestAccPostgresqlFlexibleServer_recreateWithLowerStorageMb(t *testing.T) {
+	data := acceptance.BuildTestData(t, "azurerm_postgresql_flexible_server", "test")
+	r := PostgresqlFlexibleServerResource{}
+
+	data.ResourceTest(t, r, []acceptance.TestStep{
+		{
+			Config: r.recreateWithLowerStorageMb(data, data.RandomInteger, "65536"),
+			Check: acceptance.ComposeTestCheckFunc(
+				check.That(data.ResourceName).ExistsInAzure(r),
+			),
+		},
+		data.ImportStep("administrator_password", "create_mode"),
+		{
+			Config: r.recreateWithLowerStorageMb(data, data.RandomInteger+1, "32768"),
+			Check: acceptance.ComposeTestCheckFunc(
+				check.That(data.ResourceName).ExistsInAzure(r),
+			),
+		},
+		data.ImportStep("administrator_password", "create_mode"),
+	})
+}
+
 func (PostgresqlFlexibleServerResource) Exists(ctx context.Context, clients *clients.Client, state *pluginsdk.InstanceState) (*bool, error) {
 	id, err := servers.ParseFlexibleServerID(state.ID)
 	if err != nil {
@@ -1378,3 +1400,22 @@ resource "azurerm_postgresql_flexible_server" "test" {
 }
 `, r.template(data), data.RandomInteger, storageMb, storageTier)
 }
+
+func (r PostgresqlFlexibleServerResource) recreateWithLowerStorageMb(data acceptance.TestData, nameSuffix int, storageMb string) string {
+	return fmt.Sprintf(`
+%s
+
+resource "azurerm_postgresql_flexible_server" "test" {
+  name                   = "acctest-fs-%d"
+  resource_group_name    = azurerm_resource_group.test.name
+  location               = azurerm_resource_group.test.location
+  administrator_login    = "adminTerraform"
+  administrator_password = "QAZwsx123"
+  storage_mb             = %s
+  storage_tier           = "P6"
+  version                = "12"
+  sku_name               = "GP_Standard_D2s_v3"
+  zone                   = "2"
+}
+`, r.template(data), nameSuffix, storageMb)
+}