Add MinDomains API to TopologySpreadConstraints field

pkg/api/pod/util.go

@@ -583,6 +583,35 @@ func dropDisabledFields(
 	if !utilfeature.DefaultFeatureGate.Enabled(features.IdentifyPodOS) && !podOSInUse(oldPodSpec) {
 		podSpec.OS = nil
 	}
+
+	dropDisabledTopologySpreadConstraintsFields(podSpec, oldPodSpec)
+}
+
+// dropDisabledTopologySpreadConstraintsFields removes disabled fields from PodSpec related
+// to TopologySpreadConstraints only if it is not already used by the old spec.
+func dropDisabledTopologySpreadConstraintsFields(podSpec, oldPodSpec *api.PodSpec) {
+	if !utilfeature.DefaultFeatureGate.Enabled(features.MinDomainsInPodTopologySpread) &&
+		!minDomainsInUse(oldPodSpec) &&
+		podSpec != nil {
+		for i := range podSpec.TopologySpreadConstraints {
+			podSpec.TopologySpreadConstraints[i].MinDomains = nil
+		}
+	}
+}
+
+// minDomainsInUse returns true if the pod spec is non-nil
+// and has non-nil MinDomains field in TopologySpreadConstraints.
+func minDomainsInUse(podSpec *api.PodSpec) bool {
+	if podSpec == nil {
+		return false
+	}
+
+	for _, c := range podSpec.TopologySpreadConstraints {
+		if c.MinDomains != nil {
+			return true
+		}
+	}
+	return false
 }
 
 // podOSInUse returns true if the pod spec is non-nil and has OS field set

pkg/api/pod/util_test.go

@@ -33,6 +33,7 @@ import (
 	featuregatetesting "k8s.io/component-base/featuregate/testing"
 	api "k8s.io/kubernetes/pkg/apis/core"
 	"k8s.io/kubernetes/pkg/features"
+	"k8s.io/utils/pointer"
 )
 
 func TestVisitContainers(t *testing.T) {
@@ -1519,6 +1520,173 @@ func TestHaveSameExpandedDNSConfig(t *testing.T) {
 	}
 }
 
+func TestDropDisabledTopologySpreadConstraintsFields(t *testing.T) {
+	testCases := []struct {
+		name        string
+		enabled     bool
+		podSpec     *api.PodSpec
+		oldPodSpec  *api.PodSpec
+		wantPodSpec *api.PodSpec
+	}{
+		{
+			name:        "TopologySpreadConstraints is nil",
+			podSpec:     &api.PodSpec{},
+			oldPodSpec:  &api.PodSpec{},
+			wantPodSpec: &api.PodSpec{},
+		},
+		{
+			name:        "TopologySpreadConstraints is empty",
+			podSpec:     &api.PodSpec{TopologySpreadConstraints: []api.TopologySpreadConstraint{}},
+			oldPodSpec:  &api.PodSpec{TopologySpreadConstraints: []api.TopologySpreadConstraint{}},
+			wantPodSpec: &api.PodSpec{TopologySpreadConstraints: []api.TopologySpreadConstraint{}},
+		},
+		{
+			name: "TopologySpreadConstraints is not empty, but all constraints don't have minDomains",
+			podSpec: &api.PodSpec{TopologySpreadConstraints: []api.TopologySpreadConstraint{
+				{
+					MinDomains: nil,
+				},
+				{
+					MinDomains: nil,
+				},
+			}},
+			oldPodSpec: &api.PodSpec{TopologySpreadConstraints: []api.TopologySpreadConstraint{
+				{
+					MinDomains: nil,
+				},
+				{
+					MinDomains: nil,
+				},
+			}},
+			wantPodSpec: &api.PodSpec{TopologySpreadConstraints: []api.TopologySpreadConstraint{
+				{
+					MinDomains: nil,
+				},
+				{
+					MinDomains: nil,
+				},
+			}},
+		},
+		{
+			name: "one constraint in podSpec has non-empty minDomains, feature gate is disabled " +
+				"and all constraint in oldPodSpec doesn't have minDomains",
+			enabled: false,
+			podSpec: &api.PodSpec{
+				TopologySpreadConstraints: []api.TopologySpreadConstraint{
+					{
+						MinDomains: pointer.Int32(2),
+					},
+					{
+						MinDomains: nil,
+					},
+				},
+			},
+			oldPodSpec: &api.PodSpec{
+				TopologySpreadConstraints: []api.TopologySpreadConstraint{
+					{
+						MinDomains: nil,
+					},
+					{
+						MinDomains: nil,
+					},
+				},
+			},
+			wantPodSpec: &api.PodSpec{
+				TopologySpreadConstraints: []api.TopologySpreadConstraint{
+					{
+						// cleared.
+						MinDomains: nil,
+					},
+					{
+						MinDomains: nil,
+					},
+				},
+			},
+		},
+		{
+			name: "one constraint in podSpec has non-empty minDomains, feature gate is disabled " +
+				"and one constraint in oldPodSpec has minDomains",
+			enabled: false,
+			podSpec: &api.PodSpec{
+				TopologySpreadConstraints: []api.TopologySpreadConstraint{
+					{
+						MinDomains: pointer.Int32(2),
+					},
+					{
+						MinDomains: nil,
+					},
+				},
+			},
+			oldPodSpec: &api.PodSpec{
+				TopologySpreadConstraints: []api.TopologySpreadConstraint{
+					{
+						MinDomains: pointer.Int32(2),
+					},
+					{
+						MinDomains: nil,
+					},
+				},
+			},
+			wantPodSpec: &api.PodSpec{
+				TopologySpreadConstraints: []api.TopologySpreadConstraint{
+					{
+						// not cleared.
+						MinDomains: pointer.Int32(2),
+					},
+					{
+						MinDomains: nil,
+					},
+				},
+			},
+		},
+		{
+			name: "one constraint in podSpec has non-empty minDomains, feature gate is enabled" +
+				"and all constraint in oldPodSpec doesn't have minDomains",
+			enabled: true,
+			podSpec: &api.PodSpec{
+				TopologySpreadConstraints: []api.TopologySpreadConstraint{
+					{
+						MinDomains: pointer.Int32(2),
+					},
+					{
+						MinDomains: nil,
+					},
+				},
+			},
+			oldPodSpec: &api.PodSpec{
+				TopologySpreadConstraints: []api.TopologySpreadConstraint{
+					{
+						MinDomains: nil,
+					},
+					{
+						MinDomains: nil,
+					},
+				},
+			},
+			wantPodSpec: &api.PodSpec{
+				TopologySpreadConstraints: []api.TopologySpreadConstraint{
+					{
+						// not cleared.
+						MinDomains: pointer.Int32(2),
+					},
+					{
+						MinDomains: nil,
+					},
+				},
+			},
+		},
+	}
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			defer featuregatetesting.SetFeatureGateDuringTest(t, utilfeature.DefaultFeatureGate, features.MinDomainsInPodTopologySpread, tc.enabled)()
+			dropDisabledFields(tc.podSpec, nil, tc.oldPodSpec, nil)
+			if diff := cmp.Diff(tc.wantPodSpec, tc.podSpec); diff != "" {
+				t.Errorf("unexpected pod spec (-want, +got):\n%s", diff)
+			}
+		})
+	}
+}
+
 func TestDropOSField(t *testing.T) {
 	podWithOSField := func() *api.Pod {
 		osField := api.PodOS{Name: "linux"}