OCPBUGS-82584: Populate status label selector for scale subresource.

go.mod

@@ -20,8 +20,8 @@ require (
 	github.com/onsi/ginkgo/v2 v2.28.1
 	github.com/onsi/gomega v1.39.1
 	github.com/openshift-eng/openshift-tests-extension v0.0.0-20260127124016-0fed2b824818
-	github.com/openshift/api v0.0.0-20260317165824-54a3998d81eb
-	github.com/openshift/client-go v0.0.0-20260317180604-743f664b82d1
+	github.com/openshift/api v0.0.0-20260429211050-21ed4c20b122
+	github.com/openshift/client-go v0.0.0-20260429123927-c81f86abfa6a
 	github.com/openshift/cluster-api-actuator-pkg/testutils v0.0.0-20250910145856-21d03d30056d
 	github.com/openshift/cluster-control-plane-machine-set-operator v0.0.0-20251029084908-344babe6a957
 	github.com/openshift/controller-runtime-common v0.0.0-20260318085703-1812aed6dbd2

go.sum

@@ -463,10 +463,10 @@ github.com/opencontainers/selinux v1.13.0 h1:Zza88GWezyT7RLql12URvoxsbLfjFx988+L
 github.com/opencontainers/selinux v1.13.0/go.mod h1:XxWTed+A/s5NNq4GmYScVy+9jzXhGBVEOAyucdRUY8s=
 github.com/openshift-eng/openshift-tests-extension v0.0.0-20260127124016-0fed2b824818 h1:jJLE/aCAqDf8U4wc3bE1IEKgIxbb0ICjCNVFA49x/8s=
 github.com/openshift-eng/openshift-tests-extension v0.0.0-20260127124016-0fed2b824818/go.mod h1:6gkP5f2HL0meusT0Aim8icAspcD1cG055xxBZ9yC68M=
-github.com/openshift/api v0.0.0-20260317165824-54a3998d81eb h1:iwBR3mzmyE3EMFx7R3CQ9lOccTS0dNht8TW82aGITg0=
-github.com/openshift/api v0.0.0-20260317165824-54a3998d81eb/go.mod h1:pyVjK0nZ4sRs4fuQVQ4rubsJdahI1PB94LnQ8sGdvxo=
-github.com/openshift/client-go v0.0.0-20260317180604-743f664b82d1 h1:Hr/R38eg5ZJXfbiaHumjJIN1buDZwhsm4ys4npVCXH0=
-github.com/openshift/client-go v0.0.0-20260317180604-743f664b82d1/go.mod h1:Za51LlH76ALiQ/aKGBYJXmyJNkA//IDJ+I///30CA2M=
+github.com/openshift/api v0.0.0-20260429211050-21ed4c20b122 h1:Lsw4zRFaiYSDpTHaC5V7vDGLJsroJl62HpkZv4AFQfQ=
+github.com/openshift/api v0.0.0-20260429211050-21ed4c20b122/go.mod h1:pyVjK0nZ4sRs4fuQVQ4rubsJdahI1PB94LnQ8sGdvxo=
+github.com/openshift/client-go v0.0.0-20260429123927-c81f86abfa6a h1:4GR6seHvlfv0rADe+LCQx63FqSExx6gaSo8uNiyWq+c=
+github.com/openshift/client-go v0.0.0-20260429123927-c81f86abfa6a/go.mod h1:Lm7X7aYbAaKhGsNhgYaowP7hiLKwfN/w0r+Q6VlQoI8=
 github.com/openshift/cluster-api-actuator-pkg/testutils v0.0.0-20250910145856-21d03d30056d h1:+sqUThLi/lmgT5/scmmjnS6+RZFtbdxRAscNfCPyLPI=
 github.com/openshift/cluster-api-actuator-pkg/testutils v0.0.0-20250910145856-21d03d30056d/go.mod h1:9+FWWWLkVrnBo1eYhA/0Ehlq5JMgIAHtcB0IF+qV1AA=
 github.com/openshift/cluster-control-plane-machine-set-operator v0.0.0-20251029084908-344babe6a957 h1:eVnkMTFnirnoUOlAUT3Hy8WriIi1JoSrilWym3Dl8Q4=

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

@@ -660,6 +660,15 @@ 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

@@ -615,6 +615,15 @@ 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

@@ -660,6 +660,15 @@ 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.OKD.crd.yaml

@@ -615,6 +615,15 @@ 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

@@ -660,6 +660,15 @@ 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))
+}