Add pod selector to the WorkerPool scale subresource (#547)

WorkerPool already served /scale, so `kubectl scale` worked, but a HPA
pointed at one did not: the subresource declared no labelSelectorPath,
and HPA needs a selector to find the pods whose metrics it is averaging
or to compute ambiguous selectors.

https://github.com/agent-substrate/substrate/issues/198

- [x] Tests pass
- [x] Appropriate changes to documentation are included in the PR

cmd/atecontroller/internal/controllers/workerpool_controller.go

@@ -21,6 +21,7 @@ import (
 	appsv1 "k8s.io/api/apps/v1"
 	"k8s.io/apimachinery/pkg/api/equality"
 	k8errors "k8s.io/apimachinery/pkg/api/errors"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 	"k8s.io/apimachinery/pkg/runtime"
 	"k8s.io/apimachinery/pkg/types"
 	ctrl "sigs.k8s.io/controller-runtime"
@@ -98,7 +99,15 @@ func (r *WorkerPoolReconciler) applyDeployment(ctx context.Context, wp *atev1alp
 }
 
 func (r *WorkerPoolReconciler) syncStatus(ctx context.Context, wp *atev1alpha1.WorkerPool, dep *appsv1.Deployment) error {
-	want := atev1alpha1.WorkerPoolStatus{Replicas: dep.Status.Replicas}
+	selector, err := metav1.LabelSelectorAsSelector(dep.Spec.Selector)
+	if err != nil {
+		return fmt.Errorf("failed to convert Deployment selector: %w", err)
+	}
+
+	want := atev1alpha1.WorkerPoolStatus{
+		Replicas: dep.Status.Replicas,
+		Selector: selector.String(),
+	}
 	if equality.Semantic.DeepEqual(wp.Status, want) {
 		return nil
 	}

cmd/atecontroller/internal/controllers/workerpool_controller_test.go

@@ -297,7 +297,8 @@ func TestDeletedDeploymentRecreated(t *testing.T) {
 }
 
 // TestStatusReplicasPropagation verifies that the controller syncs the
-// Deployment's status.replicas into WorkerPool.status.replicas.
+// Deployment's status.replicas into WorkerPool.status.replicas, and publishes
+// the Deployment's pod selector as WorkerPool.status.selector.
 func TestStatusReplicasPropagation(t *testing.T) {
 	wp := makeWorkerPool("test-status", "default", 3, "ateom:v1")
 	if err := k8sClient.Create(testCtx, wp); err != nil {
@@ -320,6 +321,9 @@ func TestStatusReplicasPropagation(t *testing.T) {
 		if err := k8sClient.Get(ctx, types.NamespacedName{Name: wp.Name, Namespace: wp.Namespace}, current); err != nil {
 			return false, nil
 		}
+		if current.Status.Selector != "ate.dev/worker-pool="+wp.Name {
+			return false, nil
+		}
 		return current.Status.Replicas == 3, nil
 	})
 }

docs/api-guide.md

@@ -78,6 +78,13 @@ spec:
         memory: 2Gi
 ```
 
+### Status (`WorkerPoolStatus`)
+
+| Field | Type | Description |
+| :--- | :--- | :--- |
+| `replicas` | `int32` | Total number of worker pods, mirrored from the managed Deployment. |
+| `selector` | `string` | Label selector for the worker pods. |
+
 ---
 
 ## 2. ActorTemplate: The Workload Blueprint

manifests/ate-install/generated/ate.dev_workerpools.yaml

@@ -424,6 +424,9 @@ spec:
                 format: int32
                 minimum: 0
                 type: integer
+              selector:
+                description: Selector is the label selector for the worker pods.
+                type: string
             type: object
         required:
         - spec
@@ -432,6 +435,7 @@ spec:
     storage: true
     subresources:
       scale:
+        labelSelectorPath: .status.selector
         specReplicasPath: .spec.replicas
         statusReplicasPath: .status.replicas
       status: {}

pkg/api/v1alpha1/workerpool_types.go

@@ -93,6 +93,10 @@ type WorkerPoolStatus struct {
 	// +kubebuilder:validation:Minimum=0
 	// +optional
 	Replicas int32 `json:"replicas"`
+
+	// Selector is the label selector for the worker pods.
+	// +optional
+	Selector string `json:"selector,omitempty"`
 }
 
 // WorkerPool is the Schema for the workerpools API
@@ -101,7 +105,7 @@ type WorkerPoolStatus struct {
 // +kubebuilder:object:root=true
 // +kubebuilder:resource:scope=Namespaced,shortName=workerpool
 // +kubebuilder:subresource:status
-// +kubebuilder:subresource:scale:specpath=.spec.replicas,statuspath=.status.replicas
+// +kubebuilder:subresource:scale:specpath=.spec.replicas,statuspath=.status.replicas,selectorpath=.status.selector
 // +kubebuilder:printcolumn:name="Desired",type=integer,JSONPath=`.spec.replicas`
 // +kubebuilder:printcolumn:name="Replicas",type=integer,JSONPath=`.status.replicas`
 // +kubebuilder:printcolumn:name="Age",type=date,JSONPath=`.metadata.creationTimestamp`