Verify cluster in API server before deleting namespace

internal/cmd/controller/cleanup/controllers/cleanup/controller.go

@@ -16,13 +16,15 @@ import (
 	rbacv1 "k8s.io/api/rbac/v1"
 	apierrors "k8s.io/apimachinery/pkg/api/errors"
 	"k8s.io/apimachinery/pkg/api/meta"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 	"k8s.io/apimachinery/pkg/runtime"
 )
 
 type handler struct {
-	apply      apply.Apply
-	clusters   fleetcontrollers.ClusterCache
-	namespaces corecontrollers.NamespaceClient
+	apply          apply.Apply
+	clusters       fleetcontrollers.ClusterCache
+	clustersClient fleetcontrollers.ClusterClient
+	namespaces     corecontrollers.NamespaceClient
 }
 
 func Register(ctx context.Context, apply apply.Apply,
@@ -33,11 +35,13 @@ func Register(ctx context.Context, apply apply.Apply,
 	clusterRole rbaccontrollers.ClusterRoleController,
 	clusterRoleBinding rbaccontrollers.ClusterRoleBindingController,
 	namespaces corecontrollers.NamespaceController,
-	clusterCache fleetcontrollers.ClusterCache) {
+	clusterCache fleetcontrollers.ClusterCache,
+	clusterClient fleetcontrollers.ClusterClient) {
 	h := &handler{
-		apply:      apply,
-		clusters:   clusterCache,
-		namespaces: namespaces,
+		apply:          apply,
+		clusters:       clusterCache,
+		clustersClient: clusterClient,
+		namespaces:     namespaces,
 	}
 
 	clusterRole.OnChange(ctx, "managed-cleanup", func(_ string, obj *rbacv1.ClusterRole) (*rbacv1.ClusterRole, error) {
@@ -90,15 +94,29 @@ func (h *handler) cleanupNamespace(key string, obj *corev1.Namespace) (*corev1.N
 		return obj, nil
 	}
 
-	// check if the cluster for this cluster namespace still exists, otherwise clean up the namespace
-	_, err := h.clusters.Get(obj.Annotations[fleet.ClusterNamespaceAnnotation], obj.Annotations[fleet.ClusterAnnotation])
-	if apierrors.IsNotFound(err) {
-		logrus.Infof("Cleaning up fleet-managed namespace %q, cluster not found", obj.Name)
+	clusterNS := obj.Annotations[fleet.ClusterNamespaceAnnotation]
+	clusterName := obj.Annotations[fleet.ClusterAnnotation]
 
-		err = h.namespaces.Delete(key, nil)
+	// check if the cluster for this cluster namespace still exists, otherwise clean up the namespace.
+	// First consult the informer cache; if the cache reports not-found, confirm with a live API call
+	// to avoid a race where the Cluster was just created and hasn't been reflected in the cache yet.
+	_, err := h.clusters.Get(clusterNS, clusterName)
+	if !apierrors.IsNotFound(err) {
 		return obj, err
 	}
-	return obj, err
+
+	// Cache said not-found — verify against the API server before deleting.
+	_, err = h.clustersClient.Get(clusterNS, clusterName, metav1.GetOptions{})
+	if err == nil {
+		// Cluster exists in the API server; the cache is stale. Do not delete the namespace.
+		return obj, nil
+	}
+	if !apierrors.IsNotFound(err) {
+		return obj, err
+	}
+
+	logrus.Infof("Cleaning up fleet-managed namespace %q, cluster not found", obj.Name)
+	return obj, h.namespaces.Delete(key, nil)
 }
 
 func (h *handler) cleanup(obj runtime.Object) error {

internal/cmd/controller/cleanup/controllers/cleanup/controller_test.go

@@ -0,0 +1,163 @@
+package cleanup
+
+import (
+	"testing"
+
+	"github.com/rancher/wrangler/v3/pkg/generic/fake"
+	"go.uber.org/mock/gomock"
+
+	fleet "github.com/rancher/fleet/pkg/apis/fleet.cattle.io/v1alpha1"
+
+	corev1 "k8s.io/api/core/v1"
+	apierrors "k8s.io/apimachinery/pkg/api/errors"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/apimachinery/pkg/runtime/schema"
+
+	. "github.com/onsi/ginkgo/v2"
+	. "github.com/onsi/gomega"
+)
+
+func TestCleanup(t *testing.T) {
+	RegisterFailHandler(Fail)
+	RunSpecs(t, "Cleanup Controller Suite")
+}
+
+var _ = Describe("cleanupNamespace", func() {
+	var (
+		mockCtrl        *gomock.Controller
+		clusterCache    *fake.MockCacheInterface[*fleet.Cluster]
+		clusterClient   *fake.MockClientInterface[*fleet.Cluster, *fleet.ClusterList]
+		namespaceClient *fake.MockNonNamespacedClientInterface[*corev1.Namespace, *corev1.NamespaceList]
+		h               *handler
+		ns              *corev1.Namespace
+		notFound        = apierrors.NewNotFound(schema.GroupResource{Group: "fleet.cattle.io", Resource: "clusters"}, "test-cluster")
+	)
+
+	BeforeEach(func() {
+		mockCtrl = gomock.NewController(GinkgoT())
+		clusterCache = fake.NewMockCacheInterface[*fleet.Cluster](mockCtrl)
+		clusterClient = fake.NewMockClientInterface[*fleet.Cluster, *fleet.ClusterList](mockCtrl)
+		namespaceClient = fake.NewMockNonNamespacedClientInterface[*corev1.Namespace, *corev1.NamespaceList](mockCtrl)
+
+		h = &handler{
+			clusters:       clusterCache,
+			clustersClient: clusterClient,
+			namespaces:     namespaceClient,
+		}
+
+		ns = &corev1.Namespace{
+			ObjectMeta: metav1.ObjectMeta{
+				Name: "cluster-fleet-default-test-cluster-abc123",
+				Labels: map[string]string{
+					fleet.ManagedLabel: "true",
+				},
+				Annotations: map[string]string{
+					fleet.ClusterAnnotation:          "test-cluster",
+					fleet.ClusterNamespaceAnnotation: "fleet-default",
+				},
+			},
+		}
+	})
+
+	Context("when namespace has no managed label", func() {
+		It("does not delete the namespace", func() {
+			ns.Labels = map[string]string{}
+			result, err := h.cleanupNamespace(ns.Name, ns)
+			Expect(err).NotTo(HaveOccurred())
+			Expect(result).To(Equal(ns))
+		})
+	})
+
+	Context("when namespace is nil", func() {
+		It("returns nil without error", func() {
+			result, err := h.cleanupNamespace("some-key", nil)
+			Expect(err).NotTo(HaveOccurred())
+			Expect(result).To(BeNil())
+		})
+	})
+
+	Context("when cluster exists in cache", func() {
+		It("does not delete the namespace", func() {
+			clusterCache.EXPECT().
+				Get("fleet-default", "test-cluster").
+				Return(&fleet.Cluster{}, nil)
+
+			result, err := h.cleanupNamespace(ns.Name, ns)
+			Expect(err).NotTo(HaveOccurred())
+			Expect(result).To(Equal(ns))
+		})
+	})
+
+	Context("when cluster is missing from cache but exists in API server", func() {
+		// This tests the fix for the race condition described in
+		// https://github.com/rancher/fleet/issues/3830: the cleanup
+		// controller's informer cache may not yet reflect a newly created
+		// Cluster, so a not-found cache result is confirmed via a live
+		// API call before the namespace is deleted.
+		It("does not delete the namespace", func() {
+			// Cache says cluster not found (stale)
+			clusterCache.EXPECT().
+				Get("fleet-default", "test-cluster").
+				Return(nil, notFound)
+
+			// API server confirms cluster exists
+			clusterClient.EXPECT().
+				Get("fleet-default", "test-cluster", gomock.Any()).
+				Return(&fleet.Cluster{}, nil)
+
+			result, err := h.cleanupNamespace(ns.Name, ns)
+			Expect(err).NotTo(HaveOccurred())
+			Expect(result).To(Equal(ns))
+		})
+	})
+
+	Context("when cluster is missing from both cache and API server", func() {
+		It("deletes the namespace", func() {
+			clusterCache.EXPECT().
+				Get("fleet-default", "test-cluster").
+				Return(nil, notFound)
+
+			clusterClient.EXPECT().
+				Get("fleet-default", "test-cluster", gomock.Any()).
+				Return(nil, notFound)
+
+			namespaceClient.EXPECT().
+				Delete(ns.Name, gomock.Any()).
+				Return(nil)
+
+			result, err := h.cleanupNamespace(ns.Name, ns)
+			Expect(err).NotTo(HaveOccurred())
+			Expect(result).To(Equal(ns))
+		})
+	})
+
+	Context("when cache lookup returns a non-NotFound error", func() {
+		It("returns the error without deleting", func() {
+			apiErr := apierrors.NewServiceUnavailable("API server unavailable")
+			clusterCache.EXPECT().
+				Get("fleet-default", "test-cluster").
+				Return(nil, apiErr)
+
+			result, err := h.cleanupNamespace(ns.Name, ns)
+			Expect(err).To(Equal(apiErr))
+			Expect(result).To(Equal(ns))
+		})
+	})
+
+	Context("when API server lookup returns a non-NotFound error", func() {
+		It("returns the error without deleting", func() {
+			apiErr := apierrors.NewServiceUnavailable("API server unavailable")
+			clusterCache.EXPECT().
+				Get("fleet-default", "test-cluster").
+				Return(nil, notFound)
+
+			clusterClient.EXPECT().
+				Get("fleet-default", "test-cluster", gomock.Any()).
+				Return(nil, apiErr)
+
+			result, err := h.cleanupNamespace(ns.Name, ns)
+			Expect(err).To(Equal(apiErr))
+			Expect(result).To(Equal(ns))
+		})
+	})
+})

internal/cmd/controller/cleanup/controllers/controllers.go

@@ -67,6 +67,7 @@ func Register(ctx context.Context, appCtx *AppContext) error {
 		appCtx.RBAC.ClusterRoleBinding(),
 		appCtx.Core.Namespace(),
 		appCtx.Cluster().Cache(),
+		appCtx.Cluster(),
 	)
 
 	if err := appCtx.Start(ctx); err != nil {