From 30ebf5c7aca5cb7a9d1f9dab18021484638d6c61 Mon Sep 17 00:00:00 2001
From: Max Fedotov <m.a.fedotov@gmail.com>
Date: Wed, 13 Mar 2024 16:02:47 +0100
Subject: [PATCH 1/2] [clusterapi] Do not skip nodegroups with minSize=maxSize

---
 .../cloudprovider/clusterapi/clusterapi_nodegroup.go      | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/cluster-autoscaler/cloudprovider/clusterapi/clusterapi_nodegroup.go b/cluster-autoscaler/cloudprovider/clusterapi/clusterapi_nodegroup.go
index d28dc0a14f2..9a1d5ab2c91 100644
--- a/cluster-autoscaler/cloudprovider/clusterapi/clusterapi_nodegroup.go
+++ b/cluster-autoscaler/cloudprovider/clusterapi/clusterapi_nodegroup.go
@@ -18,6 +18,7 @@ package clusterapi
 
 import (
 	"fmt"
+	"k8s.io/klog/v2"
 	"math/rand"
 
 	"github.com/pkg/errors"
@@ -355,7 +356,12 @@ func newNodeGroupFromScalableResource(controller *machineController, unstructure
 	}
 
 	// Ensure the node group would have the capacity to scale
-	if scalableResource.MaxSize()-scalableResource.MinSize() < 1 {
+	// allow MinSize = 0
+	// allow MaxSize = MinSize
+	// don't allow MaxSize < MinSize
+	// don't allow MaxSize = MinSize = 0
+	if scalableResource.MaxSize()-scalableResource.MinSize() < 0 || scalableResource.MaxSize() == 0 {
+		klog.V(4).Infof("nodegroup %s has no scaling capacity, skipping", scalableResource.Name())
 		return nil, nil
 	}
 

From 6c65baa1c682cea3dab3998dfea3a939b73c01ef Mon Sep 17 00:00:00 2001
From: Max Fedotov <m.a.fedotov@gmail.com>
Date: Wed, 13 Mar 2024 18:38:12 +0100
Subject: [PATCH 2/2] [clusterapi] Update tests for nodegroups with
 minSize=maxSize

---
 .../clusterapi/clusterapi_controller_test.go        | 13 ++++++-------
 .../clusterapi/clusterapi_nodegroup_test.go         | 12 ++++++++++++
 2 files changed, 18 insertions(+), 7 deletions(-)

diff --git a/cluster-autoscaler/cloudprovider/clusterapi/clusterapi_controller_test.go b/cluster-autoscaler/cloudprovider/clusterapi/clusterapi_controller_test.go
index 359111be6bb..fc89fdae577 100644
--- a/cluster-autoscaler/cloudprovider/clusterapi/clusterapi_controller_test.go
+++ b/cluster-autoscaler/cloudprovider/clusterapi/clusterapi_controller_test.go
@@ -1043,9 +1043,8 @@ func TestControllerNodeGroupForNodeWithPositiveScalingBounds(t *testing.T) {
 		if err != nil {
 			t.Fatalf("unexpected error: %v", err)
 		}
-		// We don't scale from 0 so nodes must belong to a
-		// nodegroup that has a scale size of at least 1.
-		if ng != nil {
+		// We allow scaling if minSize=maxSize
+		if ng == nil {
 			t.Fatalf("unexpected nodegroup: %v", ng)
 		}
 	}
@@ -1124,19 +1123,19 @@ func TestControllerNodeGroups(t *testing.T) {
 		nodeGroupMaxSizeAnnotationKey: "1",
 	}
 
-	// Test #5: machineset with no scaling bounds results in no nodegroups
+	// Test #5: 5 machineset with minSize=maxSize results in a five nodegroup
 	machineSetConfigs = createMachineSetTestConfigs(namespace, clusterName, RandomString(6), 5, 1, annotations, nil)
 	if err := addTestConfigs(t, controller, machineSetConfigs...); err != nil {
 		t.Fatalf("unexpected error: %v", err)
 	}
-	assertNodegroupLen(t, controller, 0)
+	assertNodegroupLen(t, controller, 5)
 
-	// Test #6: machinedeployment with no scaling bounds results in no nodegroups
+	// Test #6: add 2 machinedeployment with minSize=maxSize
 	machineDeploymentConfigs = createMachineDeploymentTestConfigs(namespace, clusterName, RandomString(6), 2, 1, annotations, nil)
 	if err := addTestConfigs(t, controller, machineDeploymentConfigs...); err != nil {
 		t.Fatalf("unexpected error: %v", err)
 	}
-	assertNodegroupLen(t, controller, 0)
+	assertNodegroupLen(t, controller, 7)
 
 	annotations = map[string]string{
 		nodeGroupMinSizeAnnotationKey: "-1",
diff --git a/cluster-autoscaler/cloudprovider/clusterapi/clusterapi_nodegroup_test.go b/cluster-autoscaler/cloudprovider/clusterapi/clusterapi_nodegroup_test.go
index 16077e8366b..07929155224 100644
--- a/cluster-autoscaler/cloudprovider/clusterapi/clusterapi_nodegroup_test.go
+++ b/cluster-autoscaler/cloudprovider/clusterapi/clusterapi_nodegroup_test.go
@@ -109,6 +109,18 @@ func TestNodeGroupNewNodeGroupConstructor(t *testing.T) {
 		nodeCount: 5,
 		errors:    false,
 		expectNil: true,
+	}, {
+		description: "no error and expect notNil: min=max=2",
+		annotations: map[string]string{
+			nodeGroupMinSizeAnnotationKey: "2",
+			nodeGroupMaxSizeAnnotationKey: "2",
+		},
+		nodeCount: 1,
+		minSize:   2,
+		maxSize:   2,
+		replicas:  1,
+		errors:    false,
+		expectNil: false,
 	}}
 
 	newNodeGroup := func(controller *machineController, testConfig *testConfig) (*nodegroup, error) {