fix: adujust to optimal replicas

Author: maltesander

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

@@ -42,13 +42,16 @@ pub fn build_pdb(
 }
 
 /// Total number of worker replicas across all worker role groups.
+///
+/// Role groups without an explicit replica count (i.e. those left to a HorizontalPodAutoscaler)
+/// contribute nothing, as their size is not known at reconcile time.
 fn worker_count(cluster: &ValidatedCluster) -> u16 {
     cluster
         .role_group_configs
         .get(&TrinoRole::Worker)
         .into_iter()
         .flat_map(|groups| groups.values())
-        .map(|rg| rg.replicas)
+        .filter_map(|rg| rg.replicas)
         .sum()
 }
 

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

@@ -459,7 +459,9 @@ pub fn build_rolegroup_statefulset(
             .build(),
         spec: Some(StatefulSetSpec {
             pod_management_policy: Some("Parallel".to_string()),
-            replicas: Some(i32::from(role_group_config.replicas)),
+            // Forward `None` when the user did not set `replicas`, leaving the field unset on the
+            // StatefulSet so a HorizontalPodAutoscaler can own the replica count.
+            replicas: role_group_config.replicas.map(i32::from),
             selector: LabelSelector {
                 match_labels: Some(
                     cluster

rust/operator-binary/src/controller/validate.rs

@@ -291,15 +291,11 @@ pub fn validate(
 
 /// Adapts the validated [`RoleGroup`] produced by [`with_validated_config`] into the flattened
 /// [`TrinoRoleGroupConfig`] consumed by the build steps.
-///
-/// Upstream `with_validated_config` returns a [`RoleGroup`] with a `HashMap` of env overrides and an
-/// optional replica count; this converts it to the ergonomic [`RoleGroupConfig`] with an
-/// [`EnvVarSet`] and a concrete replica count (defaulting to 1).
 fn into_role_group_config(
     merged: RoleGroup<v1alpha1::TrinoConfig, JavaCommonConfig, v1alpha1::TrinoConfigOverrides>,
     vector_aggregator_config_map_name: &Option<ConfigMapName>,
 ) -> Result<TrinoRoleGroupConfig> {
-    let replicas = merged.replicas.unwrap_or(1);
+    let replicas = merged.replicas;
     let common = merged.config;
 
     let mut env_overrides = EnvVarSet::new();
@@ -383,7 +379,7 @@ mod tests {
         );
         assert_eq!(
             validated.role_group_configs[&TrinoRole::Coordinator]["default"].replicas,
-            1
+            Some(1)
         );
     }
 }