fix: Keep the "none" version label on unversioned role-group resources (#892)

Author: siegfriedweber

CHANGELOG.md

@@ -30,11 +30,8 @@ All notable changes to this project will be documented in this file.
   variables set by the operator. In particular, `CONTAINERDEBUG_LOG_DIRECTORY` and the
   authentication-related environment variables can now be overridden, whereas previously the
   operator's values always took precedence ([#865]).
-- BREAKING: Remove the `app.kubernetes.io/component` and `app.kubernetes.io/role-group` labels
-  from the resources they don't apply to (previously set to `none` or a placeholder value).
-  StatefulSets created by older operator versions cannot be updated in place: after the
-  operator upgrade, delete each broker, coordinator and router StatefulSet so that the operator
-  immediately recreates it with the new labels ([#865]).
+- Remove the `app.kubernetes.io/component` and `app.kubernetes.io/role-group` labels from the
+  resources they don't apply to ([#865], [#892]).
 - Make operations infallible where dependent on static inputs ([#869], [#874]).
 - Internal operator refactoring: build each role group through per-role modules (brokers,
   coordinators, historicals, middle managers, routers) and a shared role group builder, with
@@ -73,6 +70,7 @@ All notable changes to this project will be documented in this file.
 [#888]: https://github.com/stackabletech/druid-operator/pull/888
 [#889]: https://github.com/stackabletech/druid-operator/pull/889
 [#891]: https://github.com/stackabletech/druid-operator/pull/891
+[#892]: https://github.com/stackabletech/druid-operator/pull/892
 
 ## [26.7.0] - 2026-07-21
 

rust/operator-binary/src/controller/build/container.rs

@@ -188,8 +188,7 @@ pub(crate) fn containers_and_volumes(inputs: &RoleGroupInputs) -> Result<Contain
             .add_volume_mount(&*LISTENER_VOLUME_NAME, LISTENER_VOLUME_DIR)
             .expect("The mount paths are statically defined and there should be no duplicates.");
 
-        // Used for PVC templates, which cannot be modified once they are deployed. The version
-        // label is omitted so the labels stay stable across version upgrades.
+        // The PVC template is immutable once deployed, so its labels must stay stable.
         let unversioned_recommended_labels =
             recommended_labels_for_unversioned_role_group_resources(
                 cluster,

rust/operator-binary/src/controller/build/mod.rs

@@ -3,6 +3,7 @@
 use std::{
     collections::{BTreeMap, HashSet},
     marker::PhantomData,
+    str::FromStr,
 };
 
 use snafu::{ResultExt, Snafu};
@@ -19,7 +20,7 @@ use stackable_operator::{
         kvp::label,
         types::{
             kubernetes::SecretKey,
-            operator::{RoleGroupName, RoleName},
+            operator::{ProductVersion, RoleGroupName, RoleName},
         },
     },
 };
@@ -55,6 +56,10 @@ pub mod resource;
 pub mod role_group;
 pub mod security;
 
+// Placeholder value for the `app.kubernetes.io/version` label on resources whose labels are
+// immutable once deployed. See `recommended_labels_for_unversioned_role_group_resources`.
+stackable_operator::constant!(UNVERSIONED_PRODUCT_VERSION: ProductVersion = "none");
+
 /// Returns an [`ObjectMetaBuilder`] pre-filled with the cluster's namespace, an owner
 /// reference back to the cluster, the resource `name` and the given `recommended_labels`.
 ///
@@ -114,14 +119,25 @@ pub(crate) fn recommended_labels_for_role_group_resources(
     )
 }
 
+/// The recommended labels for role-group resources that carry no product version.
+///
+/// The `app.kubernetes.io/version` label is set to the placeholder `none` rather than being
+/// omitted, because that is what operator versions up to 26.7 wrote. Omitting it would change the
+/// `volumeClaimTemplates` of already deployed StatefulSets, and since those templates are
+/// immutable, Kubernetes rejects the update and the operator can no longer reconcile the
+/// StatefulSet.
+///
+/// This is also why `label::recommended_labels_for_unversioned_role_group_resources`, which drops
+/// the label entirely, is not used here.
 pub(crate) fn recommended_labels_for_unversioned_role_group_resources(
     cluster: &ValidatedCluster,
     role_name: &RoleName,
     role_group_name: &RoleGroupName,
 ) -> Labels {
-    label::recommended_labels_for_unversioned_role_group_resources(
+    label::recommended_labels_for_role_group_resources(
         &cluster.name,
         &PRODUCT_NAME,
+        &UNVERSIONED_PRODUCT_VERSION,
         &OPERATOR_NAME,
         &CONTROLLER_NAME,
         role_name,
@@ -483,7 +499,7 @@ mod tests {
     use strum::IntoEnumIterator;
 
     use super::{
-        KubernetesResources, Prepared, SecretKey, build,
+        KubernetesResources, Prepared, SecretKey, UNVERSIONED_PRODUCT_VERSION, build,
         container::{
             DRUID_CONFIG_VOLUME_NAME, HDFS_CONFIG_VOLUME_NAME, LOG_CONFIG_VOLUME_NAME,
             LOG_VOLUME_NAME, RW_CONFIG_VOLUME_NAME,
@@ -752,6 +768,12 @@ spec:
             .expect("the ConfigMap has data")
     }
 
+    #[test]
+    fn test_constants() {
+        // Test that dereferencing the constant does not panic.
+        let _ = *UNVERSIONED_PRODUCT_VERSION;
+    }
+
     /// A pod's `volumes` are an ordered list: reordering them changes the pod template of every
     /// running StatefulSet and so restarts its pods. Pinned on the fixture that has every
     /// optional volume: the operator-managed volumes first, the Historical segment cache after