Add feature flag to allow enabling otel for internal metrics (#4912)

* Add feature flag to allow enabling otel for internal metrics

* Add changelog; mark existing constant deprecated; keep feature flag private

* Register feature flag in telemetry instead

* apply the feature flag back to original value in test

* change comment

* Update service/telemetry.go

update description with suggested change

Co-authored-by: Anthony Mirabella <a9@aneurysm9.com>

* Remove use of deprecated variable to address lint issue

* re-arrange import

* Fix unit test

* Re-enable the default value to be configtelemetry.UseOpenTelemetryForInternalMetrics

Co-authored-by: Anthony Mirabella <a9@aneurysm9.com>
Co-authored-by: Bogdan Drutu <bogdandrutu@gmail.com>
Co-authored-by: Bogdan Drutu <lazy@splunk.com>

CHANGELOG.md

@@ -30,6 +30,7 @@
   - Deprecated `receiverhelper.WithMetrics` in favour of `component.WithMetricsReceiver`
   - Deprecated `receiverhelper.WithLogs` in favour of `component.WithLogsReceiver`
   - Deprecated `receiverhelper.NewFactory` in favour of `component.NewReceiverFactory`
+- Change otel collector to enable open telemetry metrics through feature gate instead of a constant
 - Remove support for legacy otlp/http port. (#4916)
 - Remove deprecated funcs in pdata (#4809)
 - Remove deprecated Retrieve funcs/calls (#4922)

config/configtelemetry/configtelemetry.go

@@ -36,6 +36,8 @@ const (
 	levelDetailedStr = "detailed"
 )
 
+// Deprecated: UseOpenTelemetryForInternalMetrics has been deprecated. Uses feature flag in
+// telemetry.useOtelForInternalMetrics to handle this feature
 const UseOpenTelemetryForInternalMetrics = false
 
 // Level is the level of internal telemetry (metrics, logs, traces about the component itself)

service/collector_test.go

@@ -38,6 +38,7 @@ import (
 	"go.opentelemetry.io/collector/component"
 	"go.opentelemetry.io/collector/internal/testcomponents"
 	"go.opentelemetry.io/collector/internal/testutil"
+	"go.opentelemetry.io/collector/service/featuregate"
 )
 
 // TestCollector_StartAsGoRoutine must be the first unit test on the file,
@@ -80,7 +81,7 @@ func TestCollector_StartAsGoRoutine(t *testing.T) {
 	}, time.Second*2, time.Millisecond*200)
 }
 
-func TestCollector_Start(t *testing.T) {
+func testCollectorStartHelper(t *testing.T) {
 	factories, err := testcomponents.NewDefaultFactories()
 	require.NoError(t, err)
 	var once sync.Once
@@ -135,6 +136,31 @@ func TestCollector_Start(t *testing.T) {
 	}, time.Second*2, time.Millisecond*200)
 }
 
+// as telemetry instance is initialized only once, we need to reset it before each test so the metrics endpoint can
+// have correct handler spawned
+func resetCollectorTelemetry() {
+	collectorTelemetry = &colTelemetry{}
+}
+
+func TestCollector_Start(t *testing.T) {
+	resetCollectorTelemetry()
+	testCollectorStartHelper(t)
+}
+
+func TestCollector_StartWithOtelInternalMetrics(t *testing.T) {
+	resetCollectorTelemetry()
+	originalFlag := featuregate.IsEnabled(useOtelForInternalMetricsfeatureGateID)
+	defer func() {
+		featuregate.Apply(map[string]bool{
+			useOtelForInternalMetricsfeatureGateID: originalFlag,
+		})
+	}()
+	featuregate.Apply(map[string]bool{
+		useOtelForInternalMetricsfeatureGateID: true,
+	})
+	testCollectorStartHelper(t)
+}
+
 // TestCollector_ShutdownNoop verifies that shutdown can be called even if a collector
 // has yet to be started and it will execute without error.
 func TestCollector_ShutdownNoop(t *testing.T) {

service/telemetry.go

@@ -38,6 +38,7 @@ import (
 	"go.opentelemetry.io/collector/internal/version"
 	semconv "go.opentelemetry.io/collector/model/semconv/v1.5.0"
 	"go.opentelemetry.io/collector/processor/batchprocessor"
+	"go.opentelemetry.io/collector/service/featuregate"
 	telemetry2 "go.opentelemetry.io/collector/service/internal/telemetry"
 )
 
@@ -50,8 +51,21 @@ const AddCollectorVersionTag = true
 const (
 	zapKeyTelemetryAddress = "address"
 	zapKeyTelemetryLevel   = "level"
+
+	// useOtelForInternalMetricsfeatureGateID is the feature gate ID that controls whether the collector uses open
+	// telemetry for internal metrics.
+	useOtelForInternalMetricsfeatureGateID = "telemetry.useOtelForInternalMetrics"
 )
 
+func init() {
+	//nolint:staticcheck
+	featuregate.Register(featuregate.Gate{
+		ID:          useOtelForInternalMetricsfeatureGateID,
+		Description: "controls whether the collector to uses open telemetry for internal metrics",
+		Enabled:     configtelemetry.UseOpenTelemetryForInternalMetrics,
+	})
+}
+
 type collectorTelemetryExporter interface {
 	init(col *Collector) error
 	shutdown() error
@@ -98,7 +112,7 @@ func (tel *colTelemetry) initOnce(col *Collector) error {
 	instanceID := instanceUUID.String()
 
 	var pe http.Handler
-	if configtelemetry.UseOpenTelemetryForInternalMetrics {
+	if featuregate.IsEnabled(useOtelForInternalMetricsfeatureGateID) {
 		otelHandler, err := tel.initOpenTelemetry()
 		if err != nil {
 			return err