Make ToSystemAffinity deterministic by sorting MatchLabels keys

changelogs/unreleased/9898-kaovilai

@@ -0,0 +1 @@
+Make ToSystemAffinity deterministic by sorting MatchLabels keys to avoid spurious affinity spec diffs and restarts

pkg/util/kube/pod.go

@@ -20,6 +20,7 @@ import (
 	"fmt"
 	"io"
 	"os"
+	"sort"
 	"strings"
 	"time"
 
@@ -236,7 +237,20 @@ func CollectPodLogs(ctx context.Context, podGetter corev1client.CoreV1Interface,
 func ToSystemAffinity(loadAffinity *LoadAffinity, volumeTopology *corev1api.NodeSelector) *corev1api.Affinity {
 	requirements := []corev1api.NodeSelectorRequirement{}
 	if loadAffinity != nil {
-		for k, v := range loadAffinity.NodeSelector.MatchLabels {
+		// MatchLabels is a map, so its iteration order is not deterministic.
+		// Sort the keys so the generated requirements (and therefore the
+		// resulting affinity) have a stable order. This output may be embedded
+		// into objects that are reconciled continuously (e.g. DaemonSet pod
+		// templates), where an order-only difference would be treated as a spec
+		// change and trigger unnecessary rollouts/restarts.
+		keys := make([]string, 0, len(loadAffinity.NodeSelector.MatchLabels))
+		for k := range loadAffinity.NodeSelector.MatchLabels {
+			keys = append(keys, k)
+		}
+		sort.Strings(keys)
+
+		for _, k := range keys {
+			v := loadAffinity.NodeSelector.MatchLabels[k]
 			requirements = append(requirements, corev1api.NodeSelectorRequirement{
 				Key:      k,
 				Values:   []string{v},

pkg/util/kube/pod_test.go

@@ -834,6 +834,45 @@ func TestToSystemAffinity(t *testing.T) {
 				},
 			},
 		},
+		{
+			name: "with multiple match labels are sorted by key",
+			loadAffinity: &LoadAffinity{
+				NodeSelector: metav1.LabelSelector{
+					MatchLabels: map[string]string{
+						"key-c": "value-c",
+						"key-a": "value-a",
+						"key-b": "value-b",
+					},
+				},
+			},
+			expected: &corev1api.Affinity{
+				NodeAffinity: &corev1api.NodeAffinity{
+					RequiredDuringSchedulingIgnoredDuringExecution: &corev1api.NodeSelector{
+						NodeSelectorTerms: []corev1api.NodeSelectorTerm{
+							{
+								MatchExpressions: []corev1api.NodeSelectorRequirement{
+									{
+										Key:      "key-a",
+										Values:   []string{"value-a"},
+										Operator: corev1api.NodeSelectorOpIn,
+									},
+									{
+										Key:      "key-b",
+										Values:   []string{"value-b"},
+										Operator: corev1api.NodeSelectorOpIn,
+									},
+									{
+										Key:      "key-c",
+										Values:   []string{"value-c"},
+										Operator: corev1api.NodeSelectorOpIn,
+									},
+								},
+							},
+						},
+					},
+				},
+			},
+		},
 		{
 			name: "with olume topology",
 			volumeTopology: &corev1api.NodeSelector{