fix(controller): Skip no-op infra resource updates

Author: casey-coreweave

internal/controller/common/resource.go

@@ -5,6 +5,7 @@ import (
 	"reflect"
 
 	"github.com/wandb/operator/internal/logx"
+	"k8s.io/apimachinery/pkg/api/equality"
 	apierrors "k8s.io/apimachinery/pkg/api/errors"
 	"k8s.io/apimachinery/pkg/types"
 	"sigs.k8s.io/controller-runtime/pkg/client"
@@ -64,8 +65,13 @@ func CrudResource[T client.Object](ctx context.Context, c client.Client, desired
 	actualExists := !IsNil(actual) && actual.GetName() != ""
 
 	if actualExists && desiredExists {
-		action = UpdateAction
+		// Avoid no-op updates. DeepDerivative treats desired as a semantic subset of actual,
+		// so controller-added/defaulted fields on actual do not trigger unnecessary updates.
+		if equality.Semantic.DeepDerivative(desired, actual) {
+			return NoAction, nil
+		}
 
+		action = UpdateAction
 		desired.SetResourceVersion(actual.GetResourceVersion())
 		err = c.Update(ctx, desired)
 	}

internal/controller/common/resource_test.go

@@ -0,0 +1,97 @@
+package common
+
+import (
+	"context"
+	"testing"
+
+	corev1 "k8s.io/api/core/v1"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/apimachinery/pkg/runtime"
+	"k8s.io/apimachinery/pkg/types"
+	"sigs.k8s.io/controller-runtime/pkg/client/fake"
+)
+
+func TestCrudResourceNoActionForSubsetDesired(t *testing.T) {
+	scheme := runtime.NewScheme()
+	if err := corev1.AddToScheme(scheme); err != nil {
+		t.Fatalf("failed to add corev1 scheme: %v", err)
+	}
+
+	existing := &corev1.ConfigMap{
+		ObjectMeta: metav1.ObjectMeta{
+			Name:        "cm",
+			Namespace:   "default",
+			Annotations: map[string]string{"controller-added": "true"},
+		},
+		Data: map[string]string{"key": "value"},
+	}
+
+	client := fake.NewClientBuilder().WithScheme(scheme).WithObjects(existing).Build()
+
+	actual := &corev1.ConfigMap{}
+	if err := client.Get(context.Background(), types.NamespacedName{Name: "cm", Namespace: "default"}, actual); err != nil {
+		t.Fatalf("failed to get configmap: %v", err)
+	}
+
+	desired := &corev1.ConfigMap{
+		ObjectMeta: metav1.ObjectMeta{
+			Name:      "cm",
+			Namespace: "default",
+		},
+		Data: map[string]string{"key": "value"},
+	}
+
+	action, err := CrudResource(context.Background(), client, desired, actual)
+	if err != nil {
+		t.Fatalf("CrudResource returned error: %v", err)
+	}
+	if action != NoAction {
+		t.Fatalf("expected no action, got %s", action)
+	}
+}
+
+func TestCrudResourceUpdateWhenDesiredDiffers(t *testing.T) {
+	scheme := runtime.NewScheme()
+	if err := corev1.AddToScheme(scheme); err != nil {
+		t.Fatalf("failed to add corev1 scheme: %v", err)
+	}
+
+	existing := &corev1.ConfigMap{
+		ObjectMeta: metav1.ObjectMeta{
+			Name:      "cm",
+			Namespace: "default",
+		},
+		Data: map[string]string{"key": "old"},
+	}
+
+	client := fake.NewClientBuilder().WithScheme(scheme).WithObjects(existing).Build()
+
+	actual := &corev1.ConfigMap{}
+	if err := client.Get(context.Background(), types.NamespacedName{Name: "cm", Namespace: "default"}, actual); err != nil {
+		t.Fatalf("failed to get configmap: %v", err)
+	}
+
+	desired := &corev1.ConfigMap{
+		ObjectMeta: metav1.ObjectMeta{
+			Name:      "cm",
+			Namespace: "default",
+		},
+		Data: map[string]string{"key": "new"},
+	}
+
+	action, err := CrudResource(context.Background(), client, desired, actual)
+	if err != nil {
+		t.Fatalf("CrudResource returned error: %v", err)
+	}
+	if action != UpdateAction {
+		t.Fatalf("expected update action, got %s", action)
+	}
+
+	updated := &corev1.ConfigMap{}
+	if err := client.Get(context.Background(), types.NamespacedName{Name: "cm", Namespace: "default"}, updated); err != nil {
+		t.Fatalf("failed to get updated configmap: %v", err)
+	}
+	if updated.Data["key"] != "new" {
+		t.Fatalf("expected updated data, got %q", updated.Data["key"])
+	}
+}