Default to Gen2 images for OpenShift 4.20+ with fallback to Gen1

From 4.20 onwards, clusters will be deployed with V2 images.
If the selected SKU doesn't support it, then fallback to using V1 image.

Fixes ARO-23073
Signed-off-by: Yadnesh Kulkarni <ykulkarn@redhat.com>

Author: yadneshk

pkg/installer/generateconfig.go

@@ -165,21 +165,20 @@ func (m *manager) generateInstallConfig(ctx context.Context) (*installconfig.Ins
 	// from a manifest so it can be specified in the RP's
 	// OpenShiftClusterVersions?
 
-	imageSKU := "aro_420" // Gen1 SKU (default)
+	// 4.20 onwards, we default to Gen2 images
+	imageSKU := "aro_420-v2" // Gen2 SKU (default)
 
-	// Check if any SKU requires V2 only (doesn't support V1)
-	masterRequiresV2, err := determineSkuSupportsV2Only(masterSKU)
+	// If any SKU doesn't support V2, use Gen1 images
+	masterSupportsV2, err := determineV2SkuSupport(masterSKU)
 	if err != nil {
 		return nil, nil, errors.WithStack(err)
 	}
-	workerRequiresV2, err := determineSkuSupportsV2Only(workerSKU)
+	workerSupportsV2, err := determineV2SkuSupport(workerSKU)
 	if err != nil {
 		return nil, nil, errors.WithStack(err)
 	}
-
-	// If any SKU only supports V2, use Gen2 images for the entire cluster.
-	if masterRequiresV2 || workerRequiresV2 {
-		imageSKU = "aro_420-v2"
+	if !masterSupportsV2 || !workerSupportsV2 {
+		imageSKU = "aro_420"
 	}
 
 	rhcosImage := &azuretypes.OSImage{
@@ -475,9 +474,8 @@ func determineAvailabilityZones(controlPlaneSKU, workerSKU *mgmtcompute.Resource
 	return controlPlaneZones, workerZones, nil
 }
 
-// determineSkuSupportsV2Only checks if the SKU ONLY supports HyperV Generation V2 (not V1).
-// Returns true if the SKU requires Gen2 images (supports V2 but not V1).
-func determineSkuSupportsV2Only(sku *mgmtcompute.ResourceSku) (bool, error) {
+// determineV2SkuSupport returns true if the SKU supports HyperV Generation V2
+func determineV2SkuSupport(sku *mgmtcompute.ResourceSku) (bool, error) {
 	skuCapabilities, capabilityExists := computeskus.GetCapabilityMap(sku)
 	if !capabilityExists {
 		return false, fmt.Errorf("no capabilities found for SKU %s", *sku.Name)
@@ -486,5 +484,5 @@ func determineSkuSupportsV2Only(sku *mgmtcompute.ResourceSku) (bool, error) {
 	if err != nil {
 		return false, fmt.Errorf("could not fetch HyperV generations for SKU %s: %w", *sku.Name, err)
 	}
-	return generations.Has("V2") && !generations.Has("V1"), nil
+	return generations.Has("V2"), nil
 }

pkg/installer/generateconfig_test.go

@@ -50,25 +50,25 @@ func TestVMNetworkingType(t *testing.T) {
 	}
 }
 
-func TestDetermineSkuSupportsV2Only(t *testing.T) {
+func TestDetermineV2SkuSupport(t *testing.T) {
 	for _, tt := range []struct {
 		name       string
 		sku        *mgmtcompute.ResourceSku
 		wantResult bool
 		wantErr    string
 	}{
 		{
-			name: "sku supports both V1 and V2, does not require V2",
+			name: "sku supports both V1 and V2",
 			sku: &mgmtcompute.ResourceSku{
 				Name: to.StringPtr("Standard_D8s_v3"),
 				Capabilities: &[]mgmtcompute.ResourceSkuCapabilities{
 					{Name: to.StringPtr("HyperVGenerations"), Value: to.StringPtr("V1,V2")},
 				},
 			},
-			wantResult: false,
+			wantResult: true,
 		},
 		{
-			name: "sku supports only V2, requires V2",
+			name: "sku supports only V2",
 			sku: &mgmtcompute.ResourceSku{
 				Name: to.StringPtr("Standard_D8s_v6"),
 				Capabilities: &[]mgmtcompute.ResourceSkuCapabilities{
@@ -78,7 +78,7 @@ func TestDetermineSkuSupportsV2Only(t *testing.T) {
 			wantResult: true,
 		},
 		{
-			name: "sku supports only V1, does not require V2",
+			name: "sku supports only V1",
 			sku: &mgmtcompute.ResourceSku{
 				Name: to.StringPtr("Standard_D2_v2"),
 				Capabilities: &[]mgmtcompute.ResourceSkuCapabilities{
@@ -108,7 +108,7 @@ func TestDetermineSkuSupportsV2Only(t *testing.T) {
 		},
 	} {
 		t.Run(tt.name, func(t *testing.T) {
-			result, err := determineSkuSupportsV2Only(tt.sku)
+			result, err := determineV2SkuSupport(tt.sku)
 
 			if tt.wantErr != "" {
 				if err == nil {