[apiserver] register custom field selectors with the scheme

customGetAttrs already extracted custom fields for storage-level
filtering, but the API server's request validation layer rejected
them because no FieldLabelConversionFunc was registered. Add
registerFieldLabelConversions to declare selectable fields for all
resource types that have custom field selectors.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: dilyevsky

pkg/apiserver/fieldselectors.go

@@ -6,6 +6,7 @@ import (
 	"k8s.io/apimachinery/pkg/fields"
 	"k8s.io/apimachinery/pkg/labels"
 	"k8s.io/apimachinery/pkg/runtime"
+	"k8s.io/apimachinery/pkg/runtime/schema"
 	"k8s.io/apiserver/pkg/registry/generic"
 	"sigs.k8s.io/apiserver-runtime/pkg/builder/resource"
 
@@ -41,3 +42,58 @@ func customGetAttrs(obj runtime.Object) (labels.Set, fields.Set, error) {
 
 	return labels.Set(om.Labels), fs, nil
 }
+
+// selectableFieldConversion returns a FieldLabelConversionFunc that accepts
+// metadata.name, metadata.namespace, and any additional fields.
+func selectableFieldConversion(extra ...string) func(label, value string) (string, string, error) {
+	allowed := map[string]bool{
+		"metadata.name":      true,
+		"metadata.namespace": true,
+	}
+	for _, f := range extra {
+		allowed[f] = true
+	}
+	return func(label, value string) (string, string, error) {
+		if allowed[label] {
+			return label, value, nil
+		}
+		return "", "", fmt.Errorf("%q is not a known field selector", label)
+	}
+}
+
+// registerFieldLabelConversions registers custom field selectors so the API
+// server accepts them in ?fieldSelector= query parameters. Without this
+// registration, only metadata.name and metadata.namespace are accepted.
+func registerFieldLabelConversions(s *runtime.Scheme) error {
+	if err := s.AddFieldLabelConversionFunc(
+		schema.GroupVersionKind{Group: corev1alpha2.GroupName, Version: "v1alpha2", Kind: "Domain"},
+		selectableFieldConversion("spec.zone", "status.phase"),
+	); err != nil {
+		return err
+	}
+	if err := s.AddFieldLabelConversionFunc(
+		schema.GroupVersionKind{Group: corev1alpha2.GroupName, Version: "v1alpha2", Kind: "DomainZone"},
+		selectableFieldConversion("status.phase"),
+	); err != nil {
+		return err
+	}
+	if err := s.AddFieldLabelConversionFunc(
+		schema.GroupVersionKind{Group: corev1alpha2.GroupName, Version: "v1alpha2", Kind: "Proxy"},
+		selectableFieldConversion("spec.provider"),
+	); err != nil {
+		return err
+	}
+	if err := s.AddFieldLabelConversionFunc(
+		schema.GroupVersionKind{Group: corev1alpha2.GroupName, Version: "v1alpha2", Kind: "Backend"},
+		selectableFieldConversion("spec.protocol"),
+	); err != nil {
+		return err
+	}
+	if err := s.AddFieldLabelConversionFunc(
+		schema.GroupVersionKind{Group: corev1alpha3.GroupName, Version: "v1alpha3", Kind: "DomainRecord"},
+		selectableFieldConversion("spec.zone", "spec.name", "status.type"),
+	); err != nil {
+		return err
+	}
+	return nil
+}

pkg/apiserver/manager.go

@@ -943,7 +943,7 @@ func start(
 		}
 
 		srvBuilder := builder.APIServer.
-			WithAdditionalSchemeInstallers(registerCrossVersionConversions)
+			WithAdditionalSchemeInstallers(registerCrossVersionConversions, registerFieldLabelConversions)
 		for _, r := range opts.resources {
 			srvBuilder = srvBuilder.WithResourceAndStorage(r, kineStore)
 		}