OCPBUGS-86849: Populate status label selector for scale subresource

go.mod

@@ -19,7 +19,7 @@ require (
 	github.com/onsi/ginkgo/v2 v2.23.4
 	github.com/onsi/gomega v1.37.0
 	github.com/openshift-eng/openshift-tests-extension v0.0.0-20250711173707-dc2a20e5a5f8
-	github.com/openshift/api v0.0.0-20250901120840-a638ff2e96fb
+	github.com/openshift/api v0.0.0-20260605122244-2c1c5b39566d
 	github.com/openshift/client-go v0.0.0-20250710075018-396b36f983ee
 	github.com/openshift/cluster-api-actuator-pkg/testutils v0.0.0-20250718085303-e712b1ebf374
 	github.com/openshift/cluster-control-plane-machine-set-operator v0.0.0-20250424110138-1dbf0c7a5d51

go.sum

@@ -459,6 +459,8 @@ github.com/openshift-eng/openshift-tests-extension v0.0.0-20250711173707-dc2a20e
 github.com/openshift-eng/openshift-tests-extension v0.0.0-20250711173707-dc2a20e5a5f8/go.mod h1:6gkP5f2HL0meusT0Aim8icAspcD1cG055xxBZ9yC68M=
 github.com/openshift/api v0.0.0-20250901120840-a638ff2e96fb h1:L5A3091VKSyOJb0nJto/pQyyHueoaW+4sXLO5fHrTBE=
 github.com/openshift/api v0.0.0-20250901120840-a638ff2e96fb/go.mod h1:SPLf21TYPipzCO67BURkCfK6dcIIxx0oNRVWaOyRcXM=
+github.com/openshift/api v0.0.0-20260605122244-2c1c5b39566d h1:Djz4aG2W0ypAHQEtubqbXpxeWGwdCds05w6dfz1GVWk=
+github.com/openshift/api v0.0.0-20260605122244-2c1c5b39566d/go.mod h1:SPLf21TYPipzCO67BURkCfK6dcIIxx0oNRVWaOyRcXM=
 github.com/openshift/client-go v0.0.0-20250710075018-396b36f983ee h1:tOtrrxfDEW8hK3eEsHqxsXurq/D6LcINGfprkQC3hqY=
 github.com/openshift/client-go v0.0.0-20250710075018-396b36f983ee/go.mod h1:zhRiYyNMk89llof2qEuGPWPD+joQPhCRUc2IK0SB510=
 github.com/openshift/cluster-api-actuator-pkg/testutils v0.0.0-20250718085303-e712b1ebf374 h1:ldUi0e64kdYJC2+ucB24GRXIXfMnI3NpSkcnalPqBGo=

install/0000_30_machine-api-operator_03_machineset.CustomNoUpgrade.crd.yaml

@@ -661,6 +661,15 @@ spec:
                   labels of the machine template of the MachineSet.
                 format: int32
                 type: integer
+              labelSelector:
+                description: |-
+                  labelSelector is a label selector, in string format, for Machines corresponding to the MachineSet.
+                  It is exposed via the scale subresource as status.selector.
+                  When omitted, the MachineSet controller has not yet reconciled spec.selector into status.labelSelector.
+                  When present, it must not be empty and must not exceed 4096 characters.
+                maxLength: 4096
+                minLength: 1
+                type: string
               observedGeneration:
                 description: observedGeneration reflects the generation of the most
                   recently observed MachineSet.

install/0000_30_machine-api-operator_03_machineset.Default.crd.yaml

@@ -616,6 +616,15 @@ spec:
                   labels of the machine template of the MachineSet.
                 format: int32
                 type: integer
+              labelSelector:
+                description: |-
+                  labelSelector is a label selector, in string format, for Machines corresponding to the MachineSet.
+                  It is exposed via the scale subresource as status.selector.
+                  When omitted, the MachineSet controller has not yet reconciled spec.selector into status.labelSelector.
+                  When present, it must not be empty and must not exceed 4096 characters.
+                maxLength: 4096
+                minLength: 1
+                type: string
               observedGeneration:
                 description: observedGeneration reflects the generation of the most
                   recently observed MachineSet.

install/0000_30_machine-api-operator_03_machineset.DevPreviewNoUpgrade.crd.yaml

@@ -661,6 +661,15 @@ spec:
                   labels of the machine template of the MachineSet.
                 format: int32
                 type: integer
+              labelSelector:
+                description: |-
+                  labelSelector is a label selector, in string format, for Machines corresponding to the MachineSet.
+                  It is exposed via the scale subresource as status.selector.
+                  When omitted, the MachineSet controller has not yet reconciled spec.selector into status.labelSelector.
+                  When present, it must not be empty and must not exceed 4096 characters.
+                maxLength: 4096
+                minLength: 1
+                type: string
               observedGeneration:
                 description: observedGeneration reflects the generation of the most
                   recently observed MachineSet.

install/0000_30_machine-api-operator_03_machineset.TechPreviewNoUpgrade.crd.yaml

@@ -661,6 +661,15 @@ spec:
                   labels of the machine template of the MachineSet.
                 format: int32
                 type: integer
+              labelSelector:
+                description: |-
+                  labelSelector is a label selector, in string format, for Machines corresponding to the MachineSet.
+                  It is exposed via the scale subresource as status.selector.
+                  When omitted, the MachineSet controller has not yet reconciled spec.selector into status.labelSelector.
+                  When present, it must not be empty and must not exceed 4096 characters.
+                maxLength: 4096
+                minLength: 1
+                type: string
               observedGeneration:
                 description: observedGeneration reflects the generation of the most
                   recently observed MachineSet.

pkg/controller/machineset/status.go

@@ -19,7 +19,6 @@ package machineset
 import (
 	"context"
 	"errors"
-	"fmt"
 	"reflect"
 
 	machinev1 "github.com/openshift/api/machine/v1beta1"
@@ -67,6 +66,7 @@ func (c *ReconcileMachineSet) calculateStatus(ms *machinev1.MachineSet, filtered
 	newStatus.FullyLabeledReplicas = int32(fullyLabeledReplicasCount)
 	newStatus.ReadyReplicas = int32(readyReplicasCount)
 	newStatus.AvailableReplicas = int32(availableReplicasCount)
+	newStatus.LabelSelector = metav1.FormatLabelSelector(&ms.Spec.Selector)
 	return newStatus
 }
 
@@ -80,6 +80,7 @@ func updateMachineSetStatus(c client.Client, ms *machinev1.MachineSet, newStatus
 		ms.Status.FullyLabeledReplicas == newStatus.FullyLabeledReplicas &&
 		ms.Status.ReadyReplicas == newStatus.ReadyReplicas &&
 		ms.Status.AvailableReplicas == newStatus.AvailableReplicas &&
+		ms.Status.LabelSelector == newStatus.LabelSelector &&
 		reflect.DeepEqual(ms.Status.Conditions, newStatus.Conditions) &&
 		ms.Generation == ms.Status.ObservedGeneration {
 		return ms, nil
@@ -97,13 +98,17 @@ func updateMachineSetStatus(c client.Client, ms *machinev1.MachineSet, newStatus
 		if ms.Spec.Replicas != nil {
 			replicas = *ms.Spec.Replicas
 		}
-		klog.V(4).Infof("%s", fmt.Sprintf("Updating status for %v: %s/%s, ", ms.Kind, ms.Namespace, ms.Name)+
-			fmt.Sprintf("replicas %d->%d (need %d), ", ms.Status.Replicas, newStatus.Replicas, replicas)+
-			fmt.Sprintf("fullyLabeledReplicas %d->%d, ", ms.Status.FullyLabeledReplicas, newStatus.FullyLabeledReplicas)+
-			fmt.Sprintf("readyReplicas %d->%d, ", ms.Status.ReadyReplicas, newStatus.ReadyReplicas)+
-			fmt.Sprintf("availableReplicas %d->%d, ", ms.Status.AvailableReplicas, newStatus.AvailableReplicas)+
-			fmt.Sprintf("sequence No: %v->%v", ms.Status.ObservedGeneration, newStatus.ObservedGeneration)+
-			fmt.Sprintf("conditions: %v->%v", ms.Status.Conditions, newStatus.Conditions))
+		klog.V(4).Infof(
+			"Updating status for %v: %s/%s, replicas %d->%d (need %d), fullyLabeledReplicas %d->%d, readyReplicas %d->%d, availableReplicas %d->%d, labelSelector %q->%q, sequence No: %v->%v, conditions: %v->%v",
+			ms.Kind, ms.Namespace, ms.Name,
+			ms.Status.Replicas, newStatus.Replicas, replicas,
+			ms.Status.FullyLabeledReplicas, newStatus.FullyLabeledReplicas,
+			ms.Status.ReadyReplicas, newStatus.ReadyReplicas,
+			ms.Status.AvailableReplicas, newStatus.AvailableReplicas,
+			ms.Status.LabelSelector, newStatus.LabelSelector,
+			ms.Status.ObservedGeneration, newStatus.ObservedGeneration,
+			ms.Status.Conditions, newStatus.Conditions,
+		)
 
 		ms.Status = newStatus
 		patchErr = c.Status().Patch(context.Background(), ms, client.MergeFrom(machineSetCopy))

pkg/controller/machineset/status_test.go

@@ -0,0 +1,114 @@
+/*
+Copyright 2026 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+	http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+package machineset
+
+import (
+	"context"
+	"testing"
+
+	. "github.com/onsi/gomega"
+	machinev1 "github.com/openshift/api/machine/v1beta1"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/client-go/kubernetes/scheme"
+	"sigs.k8s.io/controller-runtime/pkg/client"
+	"sigs.k8s.io/controller-runtime/pkg/client/fake"
+)
+
+// TestMachineSetStatusLabelSelectorMatchesScaleSubresource verifies that status.labelSelector is the
+// serialized label selector string expected by the CRD scale subresource (labelSelectorPath
+// -> .status.labelSelector), which the apiserver maps to autoscaling/v1 Scale status.selector.
+func TestMachineSetStatusLabelSelectorMatchesScaleSubresource(t *testing.T) {
+	tests := []struct {
+		name string
+		spec metav1.LabelSelector
+	}{
+		{
+			name: "matchLabels",
+			spec: metav1.LabelSelector{
+				MatchLabels: map[string]string{
+					"machine.openshift.io/cluster-api-cluster":    "cluster-id",
+					"machine.openshift.io/cluster-api-machineset": "workers",
+				},
+			},
+		},
+		{
+			name: "matchExpressions",
+			spec: metav1.LabelSelector{
+				MatchExpressions: []metav1.LabelSelectorRequirement{
+					{Key: "role", Operator: metav1.LabelSelectorOpIn, Values: []string{"worker", "infra"}},
+				},
+			},
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			g := NewWithT(t)
+
+			ms := &machinev1.MachineSet{
+				Spec: machinev1.MachineSetSpec{
+					Selector: tc.spec,
+				},
+			}
+
+			got := (&ReconcileMachineSet{}).calculateStatus(ms, nil).LabelSelector
+			want := metav1.FormatLabelSelector(&ms.Spec.Selector)
+			g.Expect(got).To(Equal(want), "status.labelSelector must match Scale status.selector for HPA")
+		})
+	}
+}
+
+func TestUpdateMachineSetStatusUpdatesLabelSelectorWithoutReplicaChanges(t *testing.T) {
+	t.Helper()
+
+	g := NewWithT(t)
+
+	ms := &machinev1.MachineSet{
+		ObjectMeta: metav1.ObjectMeta{
+			Name:       "machineset-test",
+			Namespace:  "openshift-machine-api",
+			Generation: 1,
+		},
+		Status: machinev1.MachineSetStatus{
+			Replicas:             0,
+			FullyLabeledReplicas: 0,
+			ReadyReplicas:        0,
+			AvailableReplicas:    0,
+			ObservedGeneration:   1,
+		},
+	}
+
+	cl := fake.NewClientBuilder().
+		WithScheme(scheme.Scheme).
+		WithRuntimeObjects(ms.DeepCopy()).
+		WithStatusSubresource(&machinev1.MachineSet{}).
+		Build()
+
+	current := &machinev1.MachineSet{}
+	key := client.ObjectKeyFromObject(ms)
+	g.Expect(cl.Get(context.Background(), key, current)).To(Succeed(), "failed to fetch machineset")
+
+	newStatus := current.Status
+	newStatus.LabelSelector = "machine.openshift.io/cluster-api-cluster=test-cluster"
+
+	updated, err := updateMachineSetStatus(cl, current, newStatus)
+	g.Expect(err).NotTo(HaveOccurred(), "failed to update machineset status")
+	g.Expect(updated.Status.LabelSelector).To(Equal(newStatus.LabelSelector))
+
+	stored := &machinev1.MachineSet{}
+	g.Expect(cl.Get(context.Background(), key, stored)).To(Succeed(), "failed to refetch machineset")
+	g.Expect(stored.Status.LabelSelector).To(Equal(newStatus.LabelSelector))
+}