podcertcontroller: skip ClusterTrustBundle updates when nothing changed

cmd/podcertcontroller/internal/signercontroller/signercontroller.go

@@ -240,6 +240,7 @@ func (c *Controller) ensureBundles(ctx context.Context) {
 			slog.InfoContext(ctx, "ClusterTrustBundle already in correct state",
 				slog.String("key", wantCTB.ObjectMeta.Name),
 			)
+			continue
 		}
 
 		ctb = ctb.DeepCopy()

cmd/podcertcontroller/internal/signercontroller/signercontroller_test.go

@@ -0,0 +1,108 @@
+// Copyright 2026 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package signercontroller
+
+import (
+	"context"
+	"testing"
+
+	"github.com/agent-substrate/substrate/internal/clustertrustbundle"
+	certsv1 "k8s.io/api/certificates/v1"
+	certsv1beta1 "k8s.io/api/certificates/v1beta1"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/client-go/kubernetes/fake"
+)
+
+type fakeSigner struct {
+	bundles []*certsv1.ClusterTrustBundle
+}
+
+func (fakeSigner) SignerName() string { return "example.com/signer" }
+
+func (f fakeSigner) DesiredClusterTrustBundles() ([]*certsv1.ClusterTrustBundle, error) {
+	return f.bundles, nil
+}
+
+func (fakeSigner) MakeCert(context.Context, *certsv1beta1.PodCertificateRequest) error {
+	return nil
+}
+
+type assignedHasher struct{}
+
+func (assignedHasher) AssignedToThisReplica(context.Context, string) bool { return true }
+
+func bundle(trust string, labels map[string]string) *certsv1.ClusterTrustBundle {
+	return &certsv1.ClusterTrustBundle{
+		ObjectMeta: metav1.ObjectMeta{Name: "example.com:signer:bundle", Labels: labels},
+		Spec:       certsv1.ClusterTrustBundleSpec{SignerName: "example.com/signer", TrustBundle: trust},
+	}
+}
+
+func TestEnsureBundles(t *testing.T) {
+	want := bundle("root-a", map[string]string{"k": "v"})
+	for _, tc := range []struct {
+		name     string
+		existing *certsv1.ClusterTrustBundle
+		wantVerb string // the single write expected, or "" for none
+	}{
+		{name: "missing", wantVerb: "create"},
+		{name: "matching", existing: bundle("root-a", map[string]string{"k": "v"})},
+		{name: "stale bundle", existing: bundle("root-old", map[string]string{"k": "v"}), wantVerb: "update"},
+		{name: "stale labels", existing: bundle("root-a", nil), wantVerb: "update"},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			kc := fake.NewSimpleClientset()
+			kc.Resources = []*metav1.APIResourceList{{
+				GroupVersion: certsv1.SchemeGroupVersion.String(),
+				APIResources: []metav1.APIResource{{Name: "clustertrustbundles"}},
+			}}
+			client, err := clustertrustbundle.NewClient(kc, nil)
+			if err != nil {
+				t.Fatal(err)
+			}
+			ctx := context.Background()
+			if tc.existing != nil {
+				if _, err := client.Create(ctx, tc.existing, metav1.CreateOptions{}); err != nil {
+					t.Fatal(err)
+				}
+			}
+			kc.ClearActions()
+
+			c := &Controller{trustBundles: client, hasher: assignedHasher{}, handler: fakeSigner{bundles: []*certsv1.ClusterTrustBundle{want}}}
+			c.ensureBundles(ctx)
+
+			var writes []string
+			for _, a := range kc.Actions() {
+				if v := a.GetVerb(); v == "create" || v == "update" {
+					writes = append(writes, v)
+				}
+			}
+			if tc.wantVerb == "" && len(writes) != 0 {
+				t.Errorf("writes = %v, want none", writes)
+			}
+			if tc.wantVerb != "" && (len(writes) != 1 || writes[0] != tc.wantVerb) {
+				t.Errorf("writes = %v, want [%s]", writes, tc.wantVerb)
+			}
+
+			got, err := client.Get(ctx, want.Name, metav1.GetOptions{})
+			if err != nil {
+				t.Fatal(err)
+			}
+			if got.Spec != want.Spec || got.Labels["k"] != "v" {
+				t.Errorf("stored = %+v, want spec %+v with label k=v", got, want.Spec)
+			}
+		})
+	}
+}