kubernetes · kubernetes-prow · Jul 7, 2026 · Jul 6, 2026 · Jul 6, 2026 · Jul 6, 2026
diff --git a/cmd/kops/integration_test.go b/cmd/kops/integration_test.go
@@ -554,6 +554,7 @@ func TestHA(t *testing.T) {
 func TestHighAvailabilityGCE(t *testing.T) {
 	newIntegrationTest("ha-gce.example.com", "ha_gce").withZones(3).
 		withAddons(
+			clusterAutoscalerAddon,
 			dnsControllerAddon,
 			gcpCCMAddon,
 			gcpPDCSIAddon,

diff --git a/pkg/model/gcemodel/autoscalinggroup.go b/pkg/model/gcemodel/autoscalinggroup.go
@@ -288,29 +288,41 @@ func (b *AutoscalingGroupModelBuilder) splitToZones(ig *kops.InstanceGroup) (map
 		// 1) no support in terraform
 		// 2) we can't steer to specific zones AFAICT, only to all zones in the region
 
-		targetSizes := make([]int, len(zones))
-		totalSize := 0
-		for i := range zones {
-			targetSizes[i] = minSize / len(zones)
-			totalSize += targetSizes[i]
-		}
-		i := 0
-		for totalSize < minSize {
-			targetSizes[i]++
-			totalSize++
-
-			i++
-			if i >= len(targetSizes) {
-				i = 0
-			}
-		}
+		return SplitCountAcrossZones(minSize, zones), nil
+	}
+}
 
-		instanceCountByZone := make(map[string]int)
-		for i, zone := range zones {
-			instanceCountByZone[zone] = targetSizes[i]
+// SplitCountAcrossZones distributes count across zones as evenly as possible,
+// assigning the remainder to zones in the order given. Both the target sizes
+// of the per-zone InstanceGroupManagers and the min/max sizes registered with
+// cluster-autoscaler are derived from this split, so they stay consistent.
+func SplitCountAcrossZones(count int, zones []string) map[string]int {
+	if len(zones) == 0 {
+		return map[string]int{}
+	}
+
+	targetSizes := make([]int, len(zones))
+	totalSize := 0
+	for i := range zones {
+		targetSizes[i] = count / len(zones)
+		totalSize += targetSizes[i]
+	}
+	i := 0
+	for totalSize < count {
+		targetSizes[i]++
+		totalSize++
+
+		i++
+		if i >= len(targetSizes) {
+			i = 0
 		}
-		return instanceCountByZone, nil
 	}
+
+	countByZone := make(map[string]int)
+	for i, zone := range zones {
+		countByZone[zone] = targetSizes[i]
+	}
+	return countByZone
 }
 
 func (b *AutoscalingGroupModelBuilder) Build(c *fi.CloudupModelBuilderContext) error {

diff --git a/tests/integration/update_cluster/ha_gce/data/aws_s3_object_cluster-completed.spec_content b/tests/integration/update_cluster/ha_gce/data/aws_s3_object_cluster-completed.spec_content
@@ -29,6 +29,23 @@ spec:
     leaderElection:
       leaderElect: true
   cloudProvider: gce
+  clusterAutoscaler:
+    awsUseStaticInstanceList: false
+    balanceSimilarNodeGroups: false
+    emitPerNodegroupMetrics: false
+    enabled: true
+    expander: random
+    ignoreDaemonSetsUtilization: false
+    image: registry.k8s.io/autoscaling/cluster-autoscaler:v1.32.7
+    maxNodeProvisionTime: 15m0s
+    newPodScaleUpDelay: 0s
+    scaleDownDelayAfterAdd: 10m0s
+    scaleDownUnneededTime: 10m0s
+    scaleDownUnreadyTime: 20m0s
+    scaleDownUtilizationThreshold: "0.5"
+    skipNodesWithCustomControllerPods: true
+    skipNodesWithLocalStorage: true
+    skipNodesWithSystemPods: true
   clusterDNSDomain: cluster.local
   configBase: memfs://tests/ha-gce.example.com
   containerd:

diff --git a/...tion/update_cluster/ha_gce/data/aws_s3_object_ha-gce.example.com-addons-bootstrap_content b/...tion/update_cluster/ha_gce/data/aws_s3_object_ha-gce.example.com-addons-bootstrap_content
@@ -33,6 +33,12 @@ spec:
     name: dns-controller.addons.k8s.io
     selector:
       k8s-addon: dns-controller.addons.k8s.io
+  - id: k8s-1.15
+    manifest: cluster-autoscaler.addons.k8s.io/k8s-1.15.yaml
+    manifestHash: d5520ffa5552a7f2cfc659fa19472299ef8e58d1fbc8117b8c33ade21157cc0f
+    name: cluster-autoscaler.addons.k8s.io
+    selector:
+      k8s-addon: cluster-autoscaler.addons.k8s.io
   - id: v1.7.0
     manifest: storage-gce.addons.k8s.io/v1.7.0.yaml
     manifestHash: 4f73c7d683f04e61d60e90053a6db1fd82272dc0c13790390740f5e207181c77