pkg/{cache,client}: add options for cache miss policy (#2406)

This commit allows users to opt out of the "start informers in the
background" behavior that the current cache implementation uses.
Additionally, when opting out of this behavior, the client can be
configured to do a live lookup on a cache miss. The default behaviors
are:

  pkg/cache: backfill data on a miss (today's default, unchanged)
  pkg/client: live lookup when cache is configured to miss

Signed-off-by: Steve Kuznetsov <skuznets@redhat.com>

Makefile

@@ -112,6 +112,7 @@ generate: $(CONTROLLER_GEN) ## Runs controller-gen for internal types for config
 
 .PHONY: clean
 clean: ## Cleanup.
+	$(GOLANGCI_LINT) cache clean
 	$(MAKE) clean-bin
 
 .PHONY: clean-bin

pkg/cache/cache.go

@@ -145,6 +145,15 @@ type Options struct {
 	// instead of `reconcile.Result{}`.
 	SyncPeriod *time.Duration
 
+	// ReaderFailOnMissingInformer configures the cache to return a ErrResourceNotCached error when a user
+	// requests, using Get() and List(), a resource the cache does not already have an informer for.
+	//
+	// This error is distinct from an errors.NotFound.
+	//
+	// Defaults to false, which means that the cache will start a new informer
+	// for every new requested resource.
+	ReaderFailOnMissingInformer bool
+
 	// DefaultNamespaces maps namespace names to cache configs. If set, only
 	// the namespaces in here will be watched and it will by used to default
 	// ByObject.Namespaces for all objects if that is nil.
@@ -329,6 +338,7 @@ func newCache(restConfig *rest.Config, opts Options) newCacheFunc {
 				Transform:             config.Transform,
 				UnsafeDisableDeepCopy: pointer.BoolDeref(config.UnsafeDisableDeepCopy, false),
 			}),
+			readerFailOnMissingInformer: opts.ReaderFailOnMissingInformer,
 		}
 	}
 }

pkg/cache/cache_test.go

@@ -18,6 +18,7 @@ package cache_test
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"reflect"
 	"sort"
@@ -117,6 +118,11 @@ func deletePod(pod client.Object) {
 var _ = Describe("Informer Cache", func() {
 	CacheTest(cache.New, cache.Options{})
 })
+
+var _ = Describe("Informer Cache with ReaderFailOnMissingInformer", func() {
+	CacheTestReaderFailOnMissingInformer(cache.New, cache.Options{ReaderFailOnMissingInformer: true})
+})
+
 var _ = Describe("Multi-Namespace Informer Cache", func() {
 	CacheTest(cache.New, cache.Options{
 		DefaultNamespaces: map[string]cache.Config{
@@ -422,6 +428,85 @@ var _ = Describe("Cache with selectors", func() {
 	})
 })
 
+func CacheTestReaderFailOnMissingInformer(createCacheFunc func(config *rest.Config, opts cache.Options) (cache.Cache, error), opts cache.Options) {
+	Describe("Cache test with ReaderFailOnMissingInformer = true", func() {
+		var (
+			informerCache       cache.Cache
+			informerCacheCtx    context.Context
+			informerCacheCancel context.CancelFunc
+			errNotCached        *cache.ErrResourceNotCached
+		)
+
+		BeforeEach(func() {
+			informerCacheCtx, informerCacheCancel = context.WithCancel(context.Background())
+			Expect(cfg).NotTo(BeNil())
+
+			By("creating the informer cache")
+			var err error
+			informerCache, err = createCacheFunc(cfg, opts)
+			Expect(err).NotTo(HaveOccurred())
+			By("running the cache and waiting for it to sync")
+			// pass as an arg so that we don't race between close and re-assign
+			go func(ctx context.Context) {
+				defer GinkgoRecover()
+				Expect(informerCache.Start(ctx)).To(Succeed())
+			}(informerCacheCtx)
+			Expect(informerCache.WaitForCacheSync(informerCacheCtx)).To(BeTrue())
+		})
+
+		AfterEach(func() {
+			informerCacheCancel()
+		})
+
+		Describe("as a Reader", func() {
+			Context("with structured objects", func() {
+				It("should not be able to list objects that haven't been watched previously", func() {
+					By("listing all services in the cluster")
+					listObj := &corev1.ServiceList{}
+					Expect(errors.As(informerCache.List(context.Background(), listObj), &errNotCached)).To(BeTrue())
+				})
+
+				It("should not be able to get objects that haven't been watched previously", func() {
+					By("getting the Kubernetes service")
+					svc := &corev1.Service{}
+					svcKey := client.ObjectKey{Namespace: "default", Name: "kubernetes"}
+					Expect(errors.As(informerCache.Get(context.Background(), svcKey, svc), &errNotCached)).To(BeTrue())
+				})
+
+				It("should be able to list objects that are configured to be watched", func() {
+					By("indicating that we need to watch services")
+					_, err := informerCache.GetInformer(context.Background(), &corev1.Service{})
+					Expect(err).ToNot(HaveOccurred())
+
+					By("listing all services in the cluster")
+					svcList := &corev1.ServiceList{}
+					Expect(informerCache.List(context.Background(), svcList)).To(Succeed())
+
+					By("verifying that the returned service looks reasonable")
+					Expect(svcList.Items).To(HaveLen(1))
+					Expect(svcList.Items[0].Name).To(Equal("kubernetes"))
+					Expect(svcList.Items[0].Namespace).To(Equal("default"))
+				})
+
+				It("should be able to get objects that are configured to be watched", func() {
+					By("indicating that we need to watch services")
+					_, err := informerCache.GetInformer(context.Background(), &corev1.Service{})
+					Expect(err).ToNot(HaveOccurred())
+
+					By("getting the Kubernetes service")
+					svc := &corev1.Service{}
+					svcKey := client.ObjectKey{Namespace: "default", Name: "kubernetes"}
+					Expect(informerCache.Get(context.Background(), svcKey, svc)).To(Succeed())
+
+					By("verifying that the returned service looks reasonable")
+					Expect(svc.Name).To(Equal("kubernetes"))
+					Expect(svc.Namespace).To(Equal("default"))
+				})
+			})
+		})
+	})
+}
+
 func CacheTest(createCacheFunc func(config *rest.Config, opts cache.Options) (cache.Cache, error), opts cache.Options) {
 	Describe("Cache test", func() {
 		var (

pkg/cache/informer_cache.go

@@ -46,11 +46,28 @@ func (*ErrCacheNotStarted) Error() string {
 	return "the cache is not started, can not read objects"
 }
 
+var _ error = (*ErrCacheNotStarted)(nil)
+
+// ErrResourceNotCached indicates that the resource type
+// the client asked the cache for is not cached, i.e. the
+// corresponding informer does not exist yet.
+type ErrResourceNotCached struct {
+	GVK schema.GroupVersionKind
+}
+
+// Error returns the error
+func (r ErrResourceNotCached) Error() string {
+	return fmt.Sprintf("%s is not cached", r.GVK.String())
+}
+
+var _ error = (*ErrResourceNotCached)(nil)
+
 // informerCache is a Kubernetes Object cache populated from internal.Informers.
 // informerCache wraps internal.Informers.
 type informerCache struct {
 	scheme *runtime.Scheme
 	*internal.Informers
+	readerFailOnMissingInformer bool
 }
 
 // Get implements Reader.
@@ -60,7 +77,7 @@ func (ic *informerCache) Get(ctx context.Context, key client.ObjectKey, out clie
 		return err
 	}
 
-	started, cache, err := ic.Informers.Get(ctx, gvk, out)
+	started, cache, err := ic.getInformerForKind(ctx, gvk, out)
 	if err != nil {
 		return err
 	}
@@ -78,7 +95,7 @@ func (ic *informerCache) List(ctx context.Context, out client.ObjectList, opts .
 		return err
 	}
 
-	started, cache, err := ic.Informers.Get(ctx, *gvk, cacheTypeObj)
+	started, cache, err := ic.getInformerForKind(ctx, *gvk, cacheTypeObj)
 	if err != nil {
 		return err
 	}
@@ -124,7 +141,7 @@ func (ic *informerCache) objectTypeForListObject(list client.ObjectList) (*schem
 	return &gvk, cacheTypeObj, nil
 }
 
-// GetInformerForKind returns the informer for the GroupVersionKind.
+// GetInformerForKind returns the informer for the GroupVersionKind. If no informer exists, one will be started.
 func (ic *informerCache) GetInformerForKind(ctx context.Context, gvk schema.GroupVersionKind) (Informer, error) {
 	// Map the gvk to an object
 	obj, err := ic.scheme.New(gvk)
@@ -139,7 +156,7 @@ func (ic *informerCache) GetInformerForKind(ctx context.Context, gvk schema.Grou
 	return i.Informer, nil
 }
 
-// GetInformer returns the informer for the obj.
+// GetInformer returns the informer for the obj. If no informer exists, one will be started.
 func (ic *informerCache) GetInformer(ctx context.Context, obj client.Object) (Informer, error) {
 	gvk, err := apiutil.GVKForObject(obj, ic.scheme)
 	if err != nil {
@@ -153,6 +170,18 @@ func (ic *informerCache) GetInformer(ctx context.Context, obj client.Object) (In
 	return i.Informer, nil
 }
 
+func (ic *informerCache) getInformerForKind(ctx context.Context, gvk schema.GroupVersionKind, obj runtime.Object) (bool, *internal.Cache, error) {
+	if ic.readerFailOnMissingInformer {
+		cache, started, ok := ic.Informers.Peek(gvk, obj)
+		if !ok {
+			return false, nil, &ErrResourceNotCached{GVK: gvk}
+		}
+		return started, cache, nil
+	}
+
+	return ic.Informers.Get(ctx, gvk, obj)
+}
+
 // NeedLeaderElection implements the LeaderElectionRunnable interface
 // to indicate that this can be started without requiring the leader lock.
 func (ic *informerCache) NeedLeaderElection() bool {

pkg/cache/internal/informers.go

@@ -230,7 +230,8 @@ func (ip *Informers) WaitForCacheSync(ctx context.Context) bool {
 	return cache.WaitForCacheSync(ctx.Done(), ip.getHasSyncedFuncs()...)
 }
 
-func (ip *Informers) get(gvk schema.GroupVersionKind, obj runtime.Object) (res *Cache, started bool, ok bool) {
+// Peek attempts to get the informer for the GVK, but does not start one if one does not exist.
+func (ip *Informers) Peek(gvk schema.GroupVersionKind, obj runtime.Object) (res *Cache, started bool, ok bool) {
 	ip.mu.RLock()
 	defer ip.mu.RUnlock()
 	i, ok := ip.informersByType(obj)[gvk]
@@ -241,7 +242,7 @@ func (ip *Informers) get(gvk schema.GroupVersionKind, obj runtime.Object) (res *
 // the Informer from the map.
 func (ip *Informers) Get(ctx context.Context, gvk schema.GroupVersionKind, obj runtime.Object) (bool, *Cache, error) {
 	// Return the informer if it is found
-	i, started, ok := ip.get(gvk, obj)
+	i, started, ok := ip.Peek(gvk, obj)
 	if !ok {
 		var err error
 		if i, started, err = ip.addInformerToMap(gvk, obj); err != nil {

pkg/client/client.go

@@ -77,10 +77,12 @@ type CacheOptions struct {
 	// Reader is a cache-backed reader that will be used to read objects from the cache.
 	// +required
 	Reader Reader
-	// DisableFor is a list of objects that should not be read from the cache.
+	// DisableFor is a list of objects that should never be read from the cache.
+	// Objects configured here always result in a live lookup.
 	DisableFor []Object
 	// Unstructured is a flag that indicates whether the cache-backed client should
 	// read unstructured objects or lists from the cache.
+	// If false, unstructured objects will always result in a live lookup.
 	Unstructured bool
 }
 
@@ -342,9 +344,11 @@ func (c *client) Get(ctx context.Context, key ObjectKey, obj Object, opts ...Get
 	if isUncached, err := c.shouldBypassCache(obj); err != nil {
 		return err
 	} else if !isUncached {
+		// Attempt to get from the cache.
 		return c.cache.Get(ctx, key, obj, opts...)
 	}
 
+	// Perform a live lookup.
 	switch obj.(type) {
 	case runtime.Unstructured:
 		return c.unstructuredClient.Get(ctx, key, obj, opts...)
@@ -362,9 +366,11 @@ func (c *client) List(ctx context.Context, obj ObjectList, opts ...ListOption) e
 	if isUncached, err := c.shouldBypassCache(obj); err != nil {
 		return err
 	} else if !isUncached {
+		// Attempt to get from the cache.
 		return c.cache.List(ctx, obj, opts...)
 	}
 
+	// Perform a live lookup.
 	switch x := obj.(type) {
 	case runtime.Unstructured:
 		return c.unstructuredClient.List(ctx, obj, opts...)

pkg/client/client_test.go

@@ -19,6 +19,7 @@ package client_test
 import (
 	"context"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"reflect"
 	"sync/atomic"
@@ -43,6 +44,7 @@ import (
 	"k8s.io/utils/pointer"
 
 	"sigs.k8s.io/controller-runtime/examples/crd/pkg"
+	"sigs.k8s.io/controller-runtime/pkg/cache"
 	"sigs.k8s.io/controller-runtime/pkg/client"
 )
 
@@ -143,6 +145,7 @@ var _ = Describe("Client", func() {
 	var count uint64 = 0
 	var replicaCount int32 = 2
 	var ns = "default"
+	var errNotCached *cache.ErrResourceNotCached
 	ctx := context.TODO()
 
 	BeforeEach(func() {
@@ -278,6 +281,16 @@ U5wwSivyi7vmegHKmblOzNVKA5qPO8zWzqBC
 			Expect(cache.Called).To(Equal(2))
 		})
 
+		It("should propagate ErrResourceNotCached errors", func() {
+			c := &fakeUncachedReader{}
+			cl, err := client.New(cfg, client.Options{Cache: &client.CacheOptions{Reader: c}})
+			Expect(err).NotTo(HaveOccurred())
+			Expect(cl).NotTo(BeNil())
+			Expect(errors.As(cl.Get(ctx, client.ObjectKey{Name: "test"}, &appsv1.Deployment{}), &errNotCached)).To(BeTrue())
+			Expect(errors.As(cl.List(ctx, &appsv1.DeploymentList{}), &errNotCached)).To(BeTrue())
+			Expect(c.Called).To(Equal(2))
+		})
+
 		It("should not use the provided reader cache if provided, on get and list for uncached GVKs", func() {
 			cache := &fakeReader{}
 			cl, err := client.New(cfg, client.Options{Cache: &client.CacheOptions{Reader: cache, DisableFor: []client.Object{&corev1.Namespace{}}}})
@@ -3938,6 +3951,20 @@ func (f *fakeReader) List(ctx context.Context, list client.ObjectList, opts ...c
 	return nil
 }
 
+type fakeUncachedReader struct {
+	Called int
+}
+
+func (f *fakeUncachedReader) Get(_ context.Context, _ client.ObjectKey, _ client.Object, opts ...client.GetOption) error {
+	f.Called++
+	return &cache.ErrResourceNotCached{}
+}
+
+func (f *fakeUncachedReader) List(_ context.Context, _ client.ObjectList, _ ...client.ListOption) error {
+	f.Called++
+	return &cache.ErrResourceNotCached{}
+}
+
 func ptr[T any](to T) *T {
 	return &to
 }

pkg/manager/manager_test.go

@@ -600,6 +600,16 @@ var _ = Describe("manger.Manager", func() {
 			cancel()
 		})
 
+		It("should be able to create a manager with a cache that fails on missing informer", func() {
+			m, err := New(cfg, Options{
+				Cache: cache.Options{
+					ReaderFailOnMissingInformer: true,
+				},
+			})
+			Expect(m).ToNot(BeNil())
+			Expect(err).ToNot(HaveOccurred())
+		})
+
 		It("should return an error if the metrics bind address is already in use", func() {
 			ln, err := net.Listen("tcp", ":0") //nolint:gosec
 			Expect(err).ShouldNot(HaveOccurred())