fix: Keep the "none" version label on unversioned role-group resources

CHANGELOG.md

@@ -29,11 +29,9 @@ All notable changes to this project will be documented in this file.
 - The discovery ConfigMap is now always written, with empty `ZOOKEEPER` and `ZOOKEEPER_HOSTS` while
   the listener publishes no addresses ([#1069]).
 - All product containers now run with `securityContext.runAsNonRoot` set to `true` to improve security ([#1070]).
-- 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 the placeholder value
-  `discovery`).
-  Server StatefulSets created by older operator versions cannot be updated in place: after the operator
-  upgrade, delete each server StatefulSet so that the operator immediately recreates it with the new labels ([#1077]).
+- 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 the placeholder value `discovery`)
+  ([#1077], [#1102]).
 - Environment variable overrides (`envOverrides`) are now merged into the operator-set
   environment variables by name, so an override replaces the operator's value instead of
   producing a duplicated entry whose precedence depended on Kubernetes' duplicate-name
@@ -69,6 +67,7 @@ All notable changes to this project will be documented in this file.
 [#1099]: https://github.com/stackabletech/zookeeper-operator/pull/1099
 [#1100]: https://github.com/stackabletech/zookeeper-operator/pull/1100
 [#1101]: https://github.com/stackabletech/zookeeper-operator/pull/1101
+[#1102]: https://github.com/stackabletech/zookeeper-operator/pull/1102
 
 ## [26.7.0] - 2026-07-21
 

rust/operator-binary/src/zk_controller/build.rs

@@ -9,7 +9,7 @@
 //! remaining submodules ([`command`], [`graceful_shutdown`], [`jvm`],
 //! [`properties`]) produce fragments that those resource builders assemble.
 
-use std::marker::PhantomData;
+use std::{marker::PhantomData, str::FromStr};
 
 use snafu::{ResultExt, Snafu};
 use stackable_operator::{
@@ -19,7 +19,7 @@ use stackable_operator::{
     v2::{
         builder::meta::ownerreference_from_resource,
         kvp::label,
-        types::operator::{RoleGroupName, RoleName},
+        types::operator::{ProductVersion, RoleGroupName, RoleName},
     },
 };
 
@@ -48,6 +48,10 @@ pub mod jvm;
 pub mod properties;
 pub mod resource;
 
+// 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");
+
 #[derive(Snafu, Debug)]
 pub enum Error {
     #[snafu(display("failed to build ConfigMap for role group {rolegroup}"))]
@@ -211,14 +215,25 @@ 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,
@@ -239,7 +254,7 @@ pub(crate) fn role_group_selector(
 mod tests {
     use stackable_operator::kube::Resource;
 
-    use super::build;
+    use super::{UNVERSIONED_PRODUCT_VERSION, build};
     use crate::zk_controller::test_support::{cluster_info, minimal_zk, validated_cluster};
 
     /// Collects the `.metadata.name`s of the given resources, sorted for stable comparison.
@@ -252,6 +267,12 @@ mod tests {
         names
     }
 
+    #[test]
+    fn test_constants() {
+        // Test that dereferencing the constant does not panic.
+        let _ = *UNVERSIONED_PRODUCT_VERSION;
+    }
+
     #[test]
     fn build_produces_expected_resource_names() {
         let zookeeper_yaml = r#"

rust/operator-binary/src/zk_controller/build/resource/statefulset.rs

@@ -205,8 +205,7 @@ pub fn build_server_rolegroup_statefulset(
     let mut cb_zookeeper = new_container_builder(&ZOOKEEPER_CONTAINER_NAME);
     let mut pod_builder = PodBuilder::new();
 
-    // 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, zk_role, role_group_name);