wait for cache sync and DAG build before starting xDS server

changelogs/unreleased/5672-therealak12-minor.md

@@ -0,0 +1,5 @@
+## Contour now waits for the cache sync before starting the DAG rebuild and XDS server
+
+Before this, we only waited for informer caches to sync but didn't wait for delivering the events to subscribed handlers.
+Now contour waits for the initial list of Kubernetes objects to be cached and processed by handlers (using the returned `HasSynced` methods)
+and then starts building its DAG and serving XDS. 

cmd/contour/serve.go

@@ -15,7 +15,6 @@
 
 import (
 	"context"
-	"errors"
 	"fmt"
 	"net"
 	"net/http"
@@ -25,6 +24,25 @@
 
 	"github.com/alecthomas/kingpin/v2"
 	envoy_server_v3 "github.com/envoyproxy/go-control-plane/pkg/server/v3"
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/sirupsen/logrus"
+	corev1 "k8s.io/api/core/v1"
+	networking_v1 "k8s.io/api/networking/v1"
+	"k8s.io/apimachinery/pkg/types"
+	"k8s.io/apimachinery/pkg/util/sets"
+	"k8s.io/apimachinery/pkg/util/wait"
+	"k8s.io/client-go/kubernetes"
+	"k8s.io/client-go/rest"
+	"k8s.io/client-go/tools/cache"
+	ctrl_cache "sigs.k8s.io/controller-runtime/pkg/cache"
+	"sigs.k8s.io/controller-runtime/pkg/client"
+	"sigs.k8s.io/controller-runtime/pkg/manager"
+	"sigs.k8s.io/controller-runtime/pkg/manager/signals"
+	controller_runtime_metrics "sigs.k8s.io/controller-runtime/pkg/metrics"
+	gatewayapi_v1beta1 "sigs.k8s.io/gateway-api/apis/v1beta1"
+
+	controller_runtime_metrics_server "sigs.k8s.io/controller-runtime/pkg/metrics/server"
+
 	contour_api_v1 "github.com/projectcontour/contour/apis/projectcontour/v1"
 	contour_api_v1alpha1 "github.com/projectcontour/contour/apis/projectcontour/v1alpha1"
 	"github.com/projectcontour/contour/internal/annotation"
@@ -46,22 +64,10 @@
 	"github.com/projectcontour/contour/internal/xdscache"
 	xdscache_v3 "github.com/projectcontour/contour/internal/xdscache/v3"
 	"github.com/projectcontour/contour/pkg/config"
-	"github.com/prometheus/client_golang/prometheus"
-	"github.com/sirupsen/logrus"
-	corev1 "k8s.io/api/core/v1"
-	networking_v1 "k8s.io/api/networking/v1"
-	"k8s.io/apimachinery/pkg/types"
-	"k8s.io/apimachinery/pkg/util/sets"
-	"k8s.io/client-go/kubernetes"
-	"k8s.io/client-go/rest"
-	"k8s.io/client-go/tools/cache"
-	ctrl_cache "sigs.k8s.io/controller-runtime/pkg/cache"
-	"sigs.k8s.io/controller-runtime/pkg/client"
-	"sigs.k8s.io/controller-runtime/pkg/manager"
-	"sigs.k8s.io/controller-runtime/pkg/manager/signals"
-	controller_runtime_metrics "sigs.k8s.io/controller-runtime/pkg/metrics"
-	controller_runtime_metrics_server "sigs.k8s.io/controller-runtime/pkg/metrics/server"
-	gatewayapi_v1beta1 "sigs.k8s.io/gateway-api/apis/v1beta1"
+)
+
+const (
+	initialDagBuildPollPeriod = 100 * time.Millisecond
 )
 
 // registerServe registers the serve subcommand and flags
@@ -176,11 +182,12 @@
 }
 
 type Server struct {
-	log        logrus.FieldLogger
-	ctx        *serveContext
-	coreClient *kubernetes.Clientset
-	mgr        manager.Manager
-	registry   *prometheus.Registry
+	log               logrus.FieldLogger
+	ctx               *serveContext
+	coreClient        *kubernetes.Clientset
+	mgr               manager.Manager
+	registry          *prometheus.Registry
+	handlerCacheSyncs []cache.InformerSynced
 }
 
 // NewServer returns a Server object which contains the initial configuration
@@ -537,14 +544,24 @@
 		contourMetrics,
 		dag.ComposeObservers(append(xdscache.ObserversOf(resources), snapshotHandler)...),
 	)
+
+	hasSynced := func() bool {
+		for _, syncFunc := range s.handlerCacheSyncs {
+			if !syncFunc() {
+				return false
+			}
+		}
+		return true
+	}
+
 	contourHandler := contour.NewEventHandler(contour.EventHandlerConfig{
 		Logger:          s.log.WithField("context", "contourEventHandler"),
 		HoldoffDelay:    100 * time.Millisecond,
 		HoldoffMaxDelay: 500 * time.Millisecond,
 		Observer:        observer,
 		StatusUpdater:   sh.Writer(),
 		Builder:         builder,
-	})
+	}, hasSynced)
 
 	// Wrap contourHandler in an EventRecorder which tracks API server events.
 	eventHandler := &contour.EventRecorder{
@@ -568,7 +585,7 @@
 
 	// Inform on the remaining resources.
 	for name, r := range informerResources {
-		if err := informOnResource(r, eventHandler, s.mgr.GetCache()); err != nil {
+		if err := s.informOnResource(r, eventHandler); err != nil {
 			s.log.WithError(err).WithField("resource", name).Fatal("failed to create informer")
 		}
 	}
@@ -584,15 +601,15 @@
 		handler = k8s.NewNamespaceFilter(sets.List(secretNamespaces), eventHandler)
 	}
 
-	if err := informOnResource(&corev1.Secret{}, handler, s.mgr.GetCache()); err != nil {
+	if err := s.informOnResource(&corev1.Secret{}, handler); err != nil {
 		s.log.WithError(err).WithField("resource", "secrets").Fatal("failed to create informer")
 	}
 
 	// Inform on endpoints.
-	if err := informOnResource(&corev1.Endpoints{}, &contour.EventRecorder{
+	if err := s.informOnResource(&corev1.Endpoints{}, &contour.EventRecorder{
 		Next:    endpointHandler,
 		Counter: contourMetrics.EventHandlerOperations,
-	}, s.mgr.GetCache()); err != nil {
+	}); err != nil {
 		s.log.WithError(err).WithField("resource", "endpoints").Fatal("failed to create informer")
 	}
 
@@ -646,7 +663,7 @@
 			handler = k8s.NewNamespaceFilter([]string{contourConfiguration.Envoy.Service.Namespace}, handler)
 		}
 
-		if err := informOnResource(&corev1.Service{}, handler, s.mgr.GetCache()); err != nil {
+		if err := s.informOnResource(&corev1.Service{}, handler); err != nil {
 			s.log.WithError(err).WithField("resource", "services").Fatal("failed to create informer")
 		}
 
@@ -657,11 +674,11 @@
 
 	xdsServer := &xdsServer{
 		log:             s.log,
-		mgr:             s.mgr,
 		registry:        s.registry,
 		config:          *contourConfiguration.XDSServer,
 		snapshotHandler: snapshotHandler,
 		resources:       resources,
+		initialDagBuilt: contourHandler.HasBuiltInitialDag,
 	}
 	if err := s.mgr.Add(xdsServer); err != nil {
 		return err
@@ -830,11 +847,11 @@
 
 type xdsServer struct {
 	log             logrus.FieldLogger
-	mgr             manager.Manager
 	registry        *prometheus.Registry
 	config          contour_api_v1alpha1.XDSServerConfig
 	snapshotHandler *xdscache.SnapshotHandler
 	resources       []xdscache.ResourceCache
+	initialDagBuilt func() bool
 }
 
 func (x *xdsServer) NeedLeaderElection() bool {
@@ -844,11 +861,13 @@
 func (x *xdsServer) Start(ctx context.Context) error {
 	log := x.log.WithField("context", "xds")
 
-	log.Printf("waiting for informer caches to sync")
-	if !x.mgr.GetCache().WaitForCacheSync(ctx) {
-		return errors.New("informer cache failed to sync")
+	log.Printf("waiting for the initial dag to be built")
+	if err := wait.PollUntilContextCancel(ctx, initialDagBuildPollPeriod, true, func(ctx context.Context) (done bool, err error) {
+		return x.initialDagBuilt(), nil
+	}); err != nil {
+		return fmt.Errorf("failed to wait for initial dag build, %w", err)
 	}
-	log.Printf("informer caches synced")
+	log.Printf("the initial dag is built")
 
 	grpcServer := xds.NewServer(x.registry, grpcOptions(log, x.config.TLS)...)
 
@@ -953,12 +972,12 @@
 		// to process, we just need informers to get events.
 		case contourConfiguration.Gateway.GatewayRef != nil:
 			// Inform on GatewayClasses.
-			if err := informOnResource(&gatewayapi_v1beta1.GatewayClass{}, eventHandler, mgr.GetCache()); err != nil {
+			if err := s.informOnResource(&gatewayapi_v1beta1.GatewayClass{}, eventHandler); err != nil {
 				s.log.WithError(err).WithField("resource", "gatewayclasses").Fatal("failed to create informer")
 			}
 
 			// Inform on Gateways.
-			if err := informOnResource(&gatewayapi_v1beta1.Gateway{}, eventHandler, mgr.GetCache()); err != nil {
+			if err := s.informOnResource(&gatewayapi_v1beta1.Gateway{}, eventHandler); err != nil {
 				s.log.WithError(err).WithField("resource", "gateways").Fatal("failed to create informer")
 			}
 		// Otherwise, run the GatewayClass and Gateway controllers to determine
@@ -1029,12 +1048,12 @@
 		}
 
 		// Inform on ReferenceGrants.
-		if err := informOnResource(&gatewayapi_v1beta1.ReferenceGrant{}, eventHandler, mgr.GetCache()); err != nil {
+		if err := s.informOnResource(&gatewayapi_v1beta1.ReferenceGrant{}, eventHandler); err != nil {
 			s.log.WithError(err).WithField("resource", "referencegrants").Fatal("failed to create informer")
 		}
 
 		// Inform on Namespaces.
-		if err := informOnResource(&corev1.Namespace{}, eventHandler, mgr.GetCache()); err != nil {
+		if err := s.informOnResource(&corev1.Namespace{}, eventHandler); err != nil {
 			s.log.WithError(err).WithField("resource", "namespaces").Fatal("failed to create informer")
 		}
 	}
@@ -1197,12 +1216,18 @@
 	return builder
 }
 
-func informOnResource(obj client.Object, handler cache.ResourceEventHandler, cache ctrl_cache.Cache) error {
-	inf, err := cache.GetInformer(context.Background(), obj)
+func (s *Server) informOnResource(obj client.Object, handler cache.ResourceEventHandler) error {
+	inf, err := s.mgr.GetCache().GetInformer(context.Background(), obj)
 	if err != nil {
 		return err
 	}
 
-	_, err = inf.AddEventHandler(handler)
-	return err
+	registration, err := inf.AddEventHandler(handler)
+
+	if err != nil {
+		return err
+	}
+
+	s.handlerCacheSyncs = append(s.handlerCacheSyncs, registration.HasSynced)
+	return nil
 }

internal/contour/handler.go

@@ -19,12 +19,16 @@
 import (
 	"context"
 	"reflect"
+	"sync/atomic"
 	"time"
 
-	"github.com/projectcontour/contour/internal/dag"
-	"github.com/projectcontour/contour/internal/k8s"
 	"github.com/sirupsen/logrus"
+	"k8s.io/client-go/tools/cache"
+	"k8s.io/client-go/tools/cache/synctrack"
 	"sigs.k8s.io/controller-runtime/pkg/client"
+
+	"github.com/projectcontour/contour/internal/dag"
+	"github.com/projectcontour/contour/internal/k8s"
 )
 
 type EventHandlerConfig struct {
@@ -55,9 +59,16 @@
 	// seq is the sequence counter of the number of times
 	// an event has been received.
 	seq int
+
+	// syncTracker is used to update/query the status of the cache sync.
+	// Uses an internal counter: incremented at item start, decremented at end.
+	// HasSynced returns true if its UpstreamHasSynced returns true and the counter is non-positive.
+	syncTracker *synctrack.SingleFileTracker
+
+	initialDagBuilt atomic.Bool
 }
 
-func NewEventHandler(config EventHandlerConfig) *EventHandler {
+func NewEventHandler(config EventHandlerConfig, upstreamHasSynced cache.InformerSynced) *EventHandler {
 	return &EventHandler{
 		FieldLogger:     config.Logger,
 		builder:         config.Builder,
@@ -67,11 +78,13 @@
 		statusUpdater:   config.StatusUpdater,
 		update:          make(chan any),
 		sequence:        make(chan int, 1),
+		syncTracker:     &synctrack.SingleFileTracker{UpstreamHasSynced: upstreamHasSynced},
 	}
 }
 
 type opAdd struct {
-	obj any
+	obj             any
+	isInInitialList bool
 }
 
 type opUpdate struct {
@@ -83,7 +96,10 @@
 }
 
 func (e *EventHandler) OnAdd(obj any, isInInitialList bool) {
-	e.update <- opAdd{obj: obj}
+	if isInInitialList {
+		e.syncTracker.Start()
+	}
+	e.update <- opAdd{obj: obj, isInInitialList: isInInitialList}
 }
 
 func (e *EventHandler) OnUpdate(oldObj, newObj any) {
@@ -94,10 +110,15 @@
 	e.update <- opDelete{obj: obj}
 }
 
+// NeedLeaderElection is included to implement manager.LeaderElectionRunnable
 func (e *EventHandler) NeedLeaderElection() bool {
 	return false
 }
 
+func (e *EventHandler) HasBuiltInitialDag() bool {
+	return e.initialDagBuilt.Load()
+}
+
 // Implements leadership.NeedLeaderElectionNotification
 func (e *EventHandler) OnElectedLeader() {
 	// Trigger an update when we are elected leader to ensure resource
@@ -164,9 +185,37 @@
 				// not to process it.
 				e.incSequence()
 			}
+
+			// We're done processing this event
+			if updateOpAdd, ok := op.(opAdd); ok {
+				if updateOpAdd.isInInitialList {
+					e.syncTracker.Finished()
+				}
+			}
 		case <-pending:
+			// Ensure informer caches are synced.
+			// Schedule a retry for dag rebuild if cache is not synced yet.
+			// Note that we can't block and wait for the cache sync as it depends on progress of this loop.
+			if !e.syncTracker.HasSynced() {
+				e.Info("skipping dag rebuild as cache is not synced")
+				timer.Reset(e.holdoffDelay)
+				break
+			}
+
 			e.WithField("last_update", time.Since(lastDAGRebuild)).WithField("outstanding", reset()).Info("performing delayed update")
-			e.rebuildDAG()
+
+			// Build a new DAG and sends it to the Observer.
+			latestDAG := e.builder.Build()
+			e.observer.OnChange(latestDAG)
+
+			// Allow XDS server to start (if it hasn't already).
+			e.initialDagBuilt.Store(true)
+
+			// Update the status on objects.
+			for _, upd := range latestDAG.StatusCache.GetStatusUpdates() {
+				e.statusUpdater.Send(upd)
+			}
+
 			e.incSequence()
 			lastDAGRebuild = time.Now()
 		case <-ctx.Done():
@@ -237,14 +286,3 @@
 	default:
 	}
 }
-
-// rebuildDAG builds a new DAG and sends it to the Observer,
-// the updates the status on objects, and updates the metrics.
-func (e *EventHandler) rebuildDAG() {
-	latestDAG := e.builder.Build()
-	e.observer.OnChange(latestDAG)
-
-	for _, upd := range latestDAG.StatusCache.GetStatusUpdates() {
-		e.statusUpdater.Send(upd)
-	}
-}