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

CHANGELOG.md

@@ -34,11 +34,8 @@
   the logger as well, because a logger discards records before any handler can filter them, so in
   that direction the UI and the other destinations open up together and cannot be set apart
   ([#829]).
-- 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 StatefulSet so that the operator immediately recreates it with
-  the new labels ([#838]).
+- Remove the `app.kubernetes.io/component` and `app.kubernetes.io/role-group` labels from the
+  resources they don't apply to ([#838], [#887]).
 - All product containers now run with `securityContext.runAsNonRoot` set to `true` to improve security ([#840]).
 - `envOverrides` names are now validated by the shared `EnvVarName` type rather than by
   operator-specific validation code ([#838]).
@@ -105,6 +102,7 @@
 [#884]: https://github.com/stackabletech/airflow-operator/pull/884
 [#885]: https://github.com/stackabletech/airflow-operator/pull/885
 [#886]: https://github.com/stackabletech/airflow-operator/pull/886
+[#887]: https://github.com/stackabletech/airflow-operator/pull/887
 
 ## [26.7.0] - 2026-07-21
 

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

@@ -1,6 +1,6 @@
 //! Builders that assemble Kubernetes resources from the validated cluster.
 
-use std::marker::PhantomData;
+use std::{marker::PhantomData, str::FromStr};
 
 use snafu::{ResultExt, Snafu};
 use stackable_operator::{
@@ -9,7 +9,7 @@ use stackable_operator::{
     v2::{
         builder::meta::ownerreference_from_resource,
         kvp::label,
-        types::operator::{RoleGroupName, RoleName},
+        types::operator::{ProductVersion, RoleGroupName, RoleName},
     },
 };
 
@@ -36,6 +36,10 @@ pub mod properties;
 pub mod resource;
 pub mod volumes;
 
+// 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 {role_group}"))]
@@ -242,14 +246,25 @@ 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,
@@ -420,14 +435,20 @@ mod tests {
     use stackable_operator::kube::Resource;
 
     use super::{
-        build,
+        UNVERSIONED_PRODUCT_VERSION, build,
         test_support::{
             app_version_label, celery_executor_cluster, cluster_with_trusted_proxies,
             kubernetes_executor_cluster, validated_cluster_with,
         },
     };
     use crate::controller::ValidatedCluster;
 
+    #[test]
+    fn test_constants() {
+        // Test that dereferencing the constant does not panic.
+        let _ = *UNVERSIONED_PRODUCT_VERSION;
+    }
+
     fn sorted_names(resources: &[impl Resource]) -> Vec<&str> {
         let mut names: Vec<&str> = resources
             .iter()

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

@@ -123,8 +123,7 @@ pub fn build_server_rolegroup_statefulset(
         airflow_role,
         role_group_name,
     );
-    // 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(
         validated_cluster,
         airflow_role,