fix(flytestdlib): initialize metrics scope and expose /metrics endpoi…

flytestdlib/app/app.go

@@ -19,6 +19,8 @@ import (
 	"github.com/flyteorg/flyte/v2/flytestdlib/config"
 	"github.com/flyteorg/flyte/v2/flytestdlib/config/viper"
 	"github.com/flyteorg/flyte/v2/flytestdlib/logger"
+	"github.com/flyteorg/flyte/v2/flytestdlib/promutils"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
 )
 
 // App is the shared entry-point skeleton for Flyte services.
@@ -81,6 +83,11 @@ func (a *App) serve(ctx context.Context) error {
 		Mux:  http.NewServeMux(),
 	}
 
+	if sc.Scope == nil {
+		sc.Scope = promutils.NewScope(a.Name)
+	}
+
+	sc.Mux.Handle("/metrics", promhttp.Handler())
 	// 3. Let the caller populate resources & register handlers
 	if err := a.Setup(ctx, sc); err != nil {
 		return fmt.Errorf("setup failed: %w", err)

flytestdlib/app/app_test.go

@@ -0,0 +1,48 @@
+package app
+
+import (
+	"context"
+	"net/http"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestApp_MetricsEndpointAndScope(t *testing.T) {
+	var capturedScope interface{}
+	setupDone := make(chan struct{})
+
+	testApp := &App{
+		Name:  "test-metrics-app",
+		Short: "Testing the metrics framework plumbing",
+		Setup: func(ctx context.Context, sc *SetupContext) error {
+			sc.Port = 8099
+			capturedScope = sc.Scope
+			close(setupDone)
+			return nil
+		},
+	}
+
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	go func() {
+		_ = testApp.serve(ctx)
+	}()
+
+	select {
+	case <-setupDone:
+	case <-time.After(2 * time.Second):
+		t.Fatal("timed out waiting for app setup")
+	}
+
+	assert.NotNil(t, capturedScope, "SetupContext.Scope should be initialized by the framework before Setup is called")
+
+	resp, err := http.Get("http://localhost:8099/metrics")
+	require.NoError(t, err)
+	defer resp.Body.Close()
+
+	assert.Equal(t, http.StatusOK, resp.StatusCode, "Expected /metrics to return a 200 OK status")
+}