[DLX] Integrate cache and watcher into dlx struct (#76)

### Description  
This PR integrates the cache and watcher components into the DLX to
enable scale-from-zero functionality based on ingress resources rather
than relying on request headers.

### Changes Made  
- Refactored initialization logic in both the ingress cache and ingress
watcher operator to support external usage from the DLX.
- Integrated `ingresscache.IngressHostCache` and `kube.IngressWatcher`
into the DLX.
- Optimize the watcher's `UpdateHandler` by adding a fast exit when the
old and new objects share the same `ResourceVersion`

### References  
- Jira ticket link - https://iguazio.atlassian.net/browse/NUC-510

### Additional Notes  
- This task will be ready for review once manual testing is complete,
including the Nuclio side.
- A separate ticket will handle integrating the cache into the
`requestHandler` as part of completing the full solution

Author: weilerN

cmd/autoscaler/app/autoscaler.go

@@ -25,6 +25,7 @@ import (
 	"time"
 
 	"github.com/v3io/scaler/pkg/autoscaler"
+	"github.com/v3io/scaler/pkg/common"
 	"github.com/v3io/scaler/pkg/pluginloader"
 	"github.com/v3io/scaler/pkg/scalertypes"
 
@@ -35,7 +36,6 @@ import (
 	"k8s.io/client-go/discovery/cached/memory"
 	"k8s.io/client-go/rest"
 	"k8s.io/client-go/restmapper"
-	"k8s.io/client-go/tools/clientcmd"
 	"k8s.io/metrics/pkg/client/custom_metrics"
 )
 
@@ -73,7 +73,7 @@ func Run(kubeconfigPath string,
 		autoScalerOptions = resourceScalerConfig.AutoScalerOptions
 	}
 
-	restConfig, err := getClientConfig(kubeconfigPath)
+	restConfig, err := common.GetClientConfig(kubeconfigPath)
 	if err != nil {
 		return errors.Wrap(err, "Failed to get client configuration")
 	}
@@ -119,11 +119,3 @@ func createAutoScaler(restConfig *rest.Config,
 
 	return newScaler, nil
 }
-
-func getClientConfig(kubeconfigPath string) (*rest.Config, error) {
-	if kubeconfigPath != "" {
-		return clientcmd.BuildConfigFromFlags("", kubeconfigPath)
-	}
-
-	return rest.InClusterConfig()
-}

cmd/dlx/app/dlx.go

@@ -24,12 +24,14 @@ import (
 	"os"
 	"time"
 
+	"github.com/v3io/scaler/pkg/common"
 	"github.com/v3io/scaler/pkg/dlx"
 	"github.com/v3io/scaler/pkg/pluginloader"
 	"github.com/v3io/scaler/pkg/scalertypes"
 
 	"github.com/nuclio/errors"
 	"github.com/nuclio/zap"
+	"k8s.io/client-go/kubernetes"
 )
 
 func Run(kubeconfigPath string,
@@ -75,6 +77,15 @@ func Run(kubeconfigPath string,
 		dlxOptions = resourceScalerConfig.DLXOptions
 	}
 
+	restConfig, err := common.GetClientConfig(kubeconfigPath)
+	if err != nil {
+		return errors.Wrap(err, "Failed to get client configuration")
+	}
+
+	if dlxOptions.KubeClientSet, err = kubernetes.NewForConfig(restConfig); err != nil {
+		return errors.Wrap(err, "Failed to create k8s client set")
+	}
+
 	newDLX, err := createDLX(resourceScaler, dlxOptions)
 	if err != nil {
 		return errors.Wrap(err, "Failed to create dlx")
@@ -88,7 +99,10 @@ func Run(kubeconfigPath string,
 	select {}
 }
 
-func createDLX(resourceScaler scalertypes.ResourceScaler, options scalertypes.DLXOptions) (*dlx.DLX, error) {
+func createDLX(
+	resourceScaler scalertypes.ResourceScaler,
+	options scalertypes.DLXOptions,
+) (*dlx.DLX, error) {
 	rootLogger, err := nucliozap.NewNuclioZap("scaler",
 		"console",
 		nil,

pkg/common/helpers.go

@@ -23,6 +23,9 @@ package common
 import (
 	"math/rand"
 	"time"
+
+	"k8s.io/client-go/rest"
+	"k8s.io/client-go/tools/clientcmd"
 )
 
 var SeededRand = rand.New(rand.NewSource(time.Now().UnixNano()))
@@ -38,3 +41,11 @@ func UniquifyStringSlice(stringList []string) []string {
 	}
 	return list
 }
+
+func GetClientConfig(kubeconfigPath string) (*rest.Config, error) {
+	if kubeconfigPath != "" {
+		return clientcmd.BuildConfigFromFlags("", kubeconfigPath)
+	}
+
+	return rest.InClusterConfig()
+}

pkg/dlx/dlx.go

@@ -24,6 +24,7 @@ import (
 	"context"
 	"net/http"
 
+	"github.com/v3io/scaler/pkg/kube"
 	"github.com/v3io/scaler/pkg/scalertypes"
 
 	"github.com/nuclio/errors"
@@ -34,6 +35,7 @@ type DLX struct {
 	logger  logger.Logger
 	handler Handler
 	server  *http.Server
+	watcher *kube.IngressWatcher
 }
 
 func NewDLX(parentLogger logger.Logger,
@@ -50,6 +52,19 @@ func NewDLX(parentLogger logger.Logger,
 		return nil, errors.Wrap(err, "Failed to create function starter")
 	}
 
+	watcher, err := kube.NewIngressWatcher(
+		context.Background(),
+		childLogger,
+		options.KubeClientSet,
+		options.ResolveTargetsFromIngressCallback,
+		options.ResyncInterval,
+		options.Namespace,
+		options.LabelSelector,
+	)
+	if err != nil {
+		return nil, errors.Wrap(err, "Failed to create ingress watcher")
+	}
+
 	handler, err := NewHandler(childLogger,
 		resourceStarter,
 		resourceScaler,
@@ -67,17 +82,25 @@ func NewDLX(parentLogger logger.Logger,
 		server: &http.Server{
 			Addr: options.ListenAddress,
 		},
+		watcher: watcher,
 	}, nil
 }
 
 func (d *DLX) Start() error {
 	d.logger.DebugWith("Starting", "server", d.server.Addr)
 	http.HandleFunc("/", d.handler.HandleFunc)
+
+	// Start the ingress watcher synchronously to ensure cache is fully synced before DLX begins handling traffic
+	if err := d.watcher.Start(); err != nil {
+		return errors.Wrap(err, "Failed to start ingress watcher")
+	}
+
 	go d.server.ListenAndServe() // nolint: errcheck
 	return nil
 }
 
 func (d *DLX) Stop(context context.Context) error {
 	d.logger.DebugWith("Stopping", "server", d.server.Addr)
+	d.watcher.Stop()
 	return d.server.Shutdown(context)
 }

pkg/ingresscache/ingresscache.go

@@ -35,7 +35,7 @@ type IngressCache struct {
 func NewIngressCache(logger logger.Logger) *IngressCache {
 	return &IngressCache{
 		syncMap: &sync.Map{},
-		logger:  logger,
+		logger:  logger.GetChild("cache"),
 	}
 }
 

pkg/ingresscache/types.go

@@ -20,15 +20,19 @@ such restriction.
 
 package ingresscache
 
+type IngressHostCacheReader interface {
+	// Get retrieves all target names for the given host and path
+	Get(host string, path string) ([]string, error)
+}
+
 type IngressHostCache interface {
+	IngressHostCacheReader
+
 	// Set adds a new item to the cache for the given host, path and targets. Will overwrite existing values if any
 	Set(host string, path string, targets []string) error
 
 	// Delete removes the specified targets from the cache for the given host and path. Will do nothing if host, path or targets do not exist
 	Delete(host string, path string, targets []string) error
-
-	// Get retrieves all target names for the given host and path
-	Get(host string, path string) ([]string, error)
 }
 
 type IngressHostsTree interface {

pkg/kube/ingress.go

@@ -22,9 +22,9 @@ package kube
 
 import (
 	"context"
-	"time"
 
 	"github.com/v3io/scaler/pkg/ingresscache"
+	"github.com/v3io/scaler/pkg/scalertypes"
 
 	"github.com/nuclio/errors"
 	"github.com/nuclio/logger"
@@ -35,29 +35,6 @@ import (
 	"k8s.io/client-go/tools/cache"
 )
 
-const (
-	defaultResyncInterval = 30 * time.Second
-)
-
-// ResolveTargetsFromIngressCallback defines a function that extracts a list of target identifiers
-// (e.g., names of services the Ingress routes traffic to) from a Kubernetes Ingress resource.
-//
-// This function is expected to be implemented externally and passed into the IngressWatcher,
-// allowing for custom logic such as parsing annotations, labels, or other ingress metadata.
-//
-// Parameters:
-//   - ingress: The Kubernetes Ingress resource to extract targets from
-//
-// Returns:
-//   - []string: A slice of target identifiers (e.g., service names, endpoint addresses)
-//   - error: An error if target resolution fails
-//
-// Implementation guidelines:
-// - Return a non-nil slice when targets are successfully resolved
-// - Return a non-nil error if resolution fails
-// - Should handle nil or malformed Ingress objects gracefully and return an error in such cases
-type ResolveTargetsFromIngressCallback func(ingress *networkingv1.Ingress) ([]string, error)
-
 type ingressValue struct {
 	name    string
 	host    string
@@ -68,31 +45,32 @@ type ingressValue struct {
 // IngressWatcher watches for changes in Kubernetes Ingress resources and updates the ingress cache accordingly
 type IngressWatcher struct {
 	ctx                    context.Context
+	cancel                 context.CancelFunc
 	logger                 logger.Logger
 	cache                  ingresscache.IngressHostCache
 	factory                informers.SharedInformerFactory
 	informer               cache.SharedIndexInformer
-	resolveTargetsCallback ResolveTargetsFromIngressCallback
+	resolveTargetsCallback scalertypes.ResolveTargetsFromIngressCallback
 }
 
 func NewIngressWatcher(
-	ctx context.Context,
+	dlxCtx context.Context,
 	dlxLogger logger.Logger,
 	kubeClient kubernetes.Interface,
-	ingressCache ingresscache.IngressCache,
-	resolveTargetsCallback ResolveTargetsFromIngressCallback,
-	resyncTimeout *time.Duration,
+	resolveTargetsCallback scalertypes.ResolveTargetsFromIngressCallback,
+	resyncInterval scalertypes.Duration,
 	namespace string,
 	labelSelector string,
 ) (*IngressWatcher, error) {
-	if resyncTimeout == nil {
-		defaultTimeout := defaultResyncInterval
-		resyncTimeout = &defaultTimeout
+	if resyncInterval.Duration == 0 {
+		resyncInterval = scalertypes.Duration{Duration: scalertypes.DefaultResyncInterval}
 	}
 
+	ctxWithCancel, cancel := context.WithCancel(dlxCtx)
+
 	factory := informers.NewSharedInformerFactoryWithOptions(
 		kubeClient,
-		*resyncTimeout,
+		resyncInterval.Duration,
 		informers.WithNamespace(namespace),
 		informers.WithTweakListOptions(func(options *metav1.ListOptions) {
 			options.LabelSelector = labelSelector
@@ -101,9 +79,10 @@ func NewIngressWatcher(
 	ingressInformer := factory.Networking().V1().Ingresses().Informer()
 
 	ingressWatcher := &IngressWatcher{
-		ctx:                    ctx,
+		ctx:                    ctxWithCancel,
+		cancel:                 cancel,
 		logger:                 dlxLogger.GetChild("watcher"),
-		cache:                  &ingressCache,
+		cache:                  ingresscache.NewIngressCache(dlxLogger),
 		factory:                factory,
 		informer:               ingressInformer,
 		resolveTargetsCallback: resolveTargetsCallback,
@@ -135,9 +114,15 @@ func (iw *IngressWatcher) Start() error {
 
 func (iw *IngressWatcher) Stop() {
 	iw.logger.Info("Stopping ingress watcher")
+	iw.cancel()
 	iw.factory.Shutdown()
 }
 
+// GetIngressHostCacheReader expose read-only access to the ingress cache
+func (iw *IngressWatcher) GetIngressHostCacheReader() ingresscache.IngressHostCacheReader {
+	return iw.cache
+}
+
 // --- ResourceEventHandler methods ---
 
 func (iw *IngressWatcher) AddHandler(obj interface{}) {
@@ -167,6 +152,26 @@ func (iw *IngressWatcher) AddHandler(obj interface{}) {
 }
 
 func (iw *IngressWatcher) UpdateHandler(oldObj, newObj interface{}) {
+	oldIngressResource, ok := oldObj.(*networkingv1.Ingress)
+	if !ok {
+		iw.logger.DebugWith("Failed to cast old object to Ingress",
+			"object", oldObj)
+		return
+	}
+
+	newIngressResource, ok := newObj.(*networkingv1.Ingress)
+	if !ok {
+		iw.logger.DebugWith("Failed to cast new object to Ingress",
+			"object", newObj)
+		return
+	}
+
+	// ResourceVersion is managed by Kubernetes and indicates whether the resource has changed.
+	// Comparing resourceVersion helps avoid unnecessary updates triggered by periodic informer resync
+	if oldIngressResource.ResourceVersion == newIngressResource.ResourceVersion {
+		return
+	}
+
 	oldIngress, err := iw.extractValuesFromIngressResource(oldObj)
 	if err != nil {
 		iw.logger.DebugWith("Update ingress handler - failed to extract values from old object",
@@ -249,7 +254,7 @@ func (iw *IngressWatcher) extractValuesFromIngressResource(obj interface{}) (*in
 
 	targets, err := iw.resolveTargetsCallback(ingress)
 	if err != nil {
-		return nil, errors.Wrap(err, "Failed to extract targets from ingress labels")
+		return nil, errors.Wrapf(err, "Failed to extract targets from ingress labels: %s", err.Error())
 	}
 
 	if len(targets) == 0 {