director: delegate candidate resolution

Refactors the Director to use the injected PodLocator interface instead
of the private getCandidatePodsForScheduling method. This prepares the
Director for lazy resolution without changing current behavior.

Author: LukeAVanDrie

pkg/epp/flowcontrol/contracts/dependencies.go

@@ -20,7 +20,6 @@ import (
 	"context"
 
 	"sigs.k8s.io/gateway-api-inference-extension/pkg/epp/backend/metrics"
-	backendmetrics "sigs.k8s.io/gateway-api-inference-extension/pkg/epp/backend/metrics"
 )
 
 // PodLocator defines the contract for a component that resolves the set of candidate pods for a request based on its
@@ -30,7 +29,7 @@ import (
 // enabling support for "Scale-from-Zero" scenarios where pods may not exist when the request is first enqueued.
 type PodLocator interface {
 	// Locate returns a list of pod metrics that match the criteria defined in the request metadata.
-	Locate(ctx context.Context, requestMetadata map[string]any) []backendmetrics.PodMetrics
+	Locate(ctx context.Context, requestMetadata map[string]any) []metrics.PodMetrics
 }
 
 // SaturationDetector defines the contract for a component that provides real-time load signals to the

pkg/epp/requestcontrol/director_test.go

@@ -651,41 +651,42 @@ func TestDirector_HandleRequest(t *testing.T) {
 			ds.PodUpdateOrAddIfNotExist(testPod)
 		}
 
-		for _, test := range tests {
-			t.Run(test.name, func(t *testing.T) {
-				mockSched := &mockScheduler{}
-				if test.schedulerMockSetup != nil {
-					test.schedulerMockSetup(mockSched)
-				}
-				config := NewConfig()
-				if test.prepareDataPlugin != nil {
-					config = config.WithPrepareDataPlugins(test.prepareDataPlugin)
-				}
-				config = config.WithAdmissionPlugins(newMockAdmissionPlugin("test-admit-plugin", test.admitRequestDenialError))
-
-				locator := NewCachedPodLocator(context.Background(), NewDatastorePodLocator(ds), time.Minute)
-				director := NewDirectorWithConfig(ds, mockSched, test.mockAdmissionController, locator, config)
-				if test.name == "successful request with model rewrite" {
-					mockDs := &mockDatastore{
-						pods:     ds.PodList(datastore.AllPodsPredicate),
-						rewrites: []*v1alpha2.InferenceModelRewrite{rewrite},
-					}
-					director.datastore = mockDs
-					director.podLocator = NewCachedPodLocator(context.Background(), NewDatastorePodLocator(mockDs), time.Minute)
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			mockSched := &mockScheduler{}
+			if test.schedulerMockSetup != nil {
+				test.schedulerMockSetup(mockSched)
+			}
+			config := NewConfig()
+			if test.prepareDataPlugin != nil {
+				config = config.WithPrepareDataPlugins(test.prepareDataPlugin)
+			}
+			config = config.WithAdmissionPlugins(newMockAdmissionPlugin("test-admit-plugin", test.admitRequestDenialError))
+
+			locator := NewCachedPodLocator(context.Background(), NewDatastorePodLocator(ds), time.Minute)
+			director := NewDirectorWithConfig(ds, mockSched, test.mockAdmissionController, locator, config)
+			if test.name == "successful request with model rewrite" {
+				mockDs := &mockDatastore{
+					pods:     ds.PodList(datastore.AllPodsPredicate),
+					rewrites: []*v1alpha2.InferenceModelRewrite{rewrite},
 				}
-				reqCtx := &handlers.RequestContext{
-					Request: &handlers.Request{
-						// Create a copy of the map for each test run to avoid mutation issues.
-						Body: make(map[string]any),
-						Headers: map[string]string{
-							requtil.RequestIdHeaderKey: "test-req-id-" + test.name, // Ensure a default request ID
-						},
+				director.datastore = mockDs
+				director.podLocator = NewCachedPodLocator(context.Background(), NewDatastorePodLocator(mockDs), time.Minute)
+			}
+
+			reqCtx := &handlers.RequestContext{
+				Request: &handlers.Request{
+					// Create a copy of the map for each test run to avoid mutation issues.
+					Body: make(map[string]any),
+					Headers: map[string]string{
+						requtil.RequestIdHeaderKey: "test-req-id-" + test.name, // Ensure a default request ID
 					},
-					ObjectiveKey:    test.inferenceObjectiveName,
-					TargetModelName: test.initialTargetModelName,
-				}
-				// Deep copy the body map.
-				maps.Copy(reqCtx.Request.Body, test.reqBodyMap)
+				},
+				ObjectiveKey:    test.inferenceObjectiveName,
+				TargetModelName: test.initialTargetModelName,
+			}
+			// Deep copy the body map.
+			maps.Copy(reqCtx.Request.Body, test.reqBodyMap)
 
 				returnedReqCtx, err := director.HandleRequest(ctx, reqCtx)
 
@@ -708,13 +709,12 @@ func TestDirector_HandleRequest(t *testing.T) {
 					assert.Equal(t, test.wantReqCtx.TargetEndpoint, returnedReqCtx.TargetEndpoint, "reqCtx.TargetEndpoint mismatch")
 				}
 
-				if test.wantMutatedBodyModel != "" {
-					assert.NotNil(t, returnedReqCtx.Request.Body, "Expected mutated body, but reqCtx.Request.Body is nil")
-					assert.Equal(t, test.wantMutatedBodyModel, returnedReqCtx.Request.Body["model"],
-						"Mutated reqCtx.Request.Body model mismatch")
-				}
-			})
-		}
+			if test.wantMutatedBodyModel != "" {
+				assert.NotNil(t, returnedReqCtx.Request.Body, "Expected mutated body, but reqCtx.Request.Body is nil")
+				assert.Equal(t, test.wantMutatedBodyModel, returnedReqCtx.Request.Body["model"],
+					"Mutated reqCtx.Request.Body model mismatch")
+			}
+		})
 	}
 }