otelx: respect explicit config and env defaults

Prefer existing tracer providers when no explicit config is set, but allow
explicit OTEL settings to override and ensure defaults honor standard env
variables.

Author: artem-tkachuk

internal/otelx/otelx_otel.go

@@ -14,8 +14,14 @@ import (
 	"go.opentelemetry.io/otel/propagation"
 	"go.opentelemetry.io/otel/sdk/resource"
 	"go.opentelemetry.io/otel/sdk/trace"
+	oteltrace "go.opentelemetry.io/otel/trace"
 	semconv "go.opentelemetry.io/otel/semconv/v1.24.0"
-	"go.opentelemetry.io/otel/trace/noop"
+)
+
+const (
+	defaultServiceName = "spegel"
+	defaultSampler     = "parentbased_always_off"
+	defaultEndpoint    = "localhost:4318"
 )
 
 // Shutdown is a function type for shutting down the OTEL SDK.
@@ -33,20 +39,24 @@ type Config struct {
 func Setup(ctx context.Context, cfg Config) (Shutdown, error) {
 	log := logr.FromContextOrDiscard(ctx)
 
-	if _, ok := otel.GetTracerProvider().(noop.TracerProvider); !ok {
+	explicitConfig := isExplicitConfig(cfg)
+	if !explicitConfig && !isNoopTracerProvider(otel.GetTracerProvider()) {
 		log.Info("skipping OTEL setup; tracer provider already configured")
 		return nil, nil
 	}
+	if explicitConfig && !isNoopTracerProvider(otel.GetTracerProvider()) {
+		log.Info("overriding existing OTEL tracer provider due to explicit config")
+	}
 
 	// Use cfg if provided, otherwise fall back to environment
 	if cfg.Endpoint == "" {
-		cfg.Endpoint = getEnv("OTEL_EXPORTER_OTLP_ENDPOINT", "http://localhost:4318")
+		cfg.Endpoint = getEnv("OTEL_EXPORTER_OTLP_ENDPOINT", defaultEndpoint)
 	}
 	if cfg.ServiceName == "" {
-		cfg.ServiceName = "spegel"
+		cfg.ServiceName = getEnv("OTEL_SERVICE_NAME", defaultServiceName)
 	}
 	if cfg.Sampler == "" {
-		cfg.Sampler = getEnv("OTEL_TRACES_SAMPLER", "parentbased_always_off")
+		cfg.Sampler = getEnv("OTEL_TRACES_SAMPLER", defaultSampler)
 	}
 
 	log.Info("initializing OTEL", "service", cfg.ServiceName, "endpoint", cfg.Endpoint, "sampler", cfg.Sampler)
@@ -102,6 +112,27 @@ func Setup(ctx context.Context, cfg Config) (Shutdown, error) {
 	return shutdownFn, nil
 }
 
+func isNoopTracerProvider(tp oteltrace.TracerProvider) bool {
+	tracer := tp.Tracer("spegel-otel-probe")
+	_, span := tracer.Start(context.Background(), "otel-probe")
+	spanCtx := span.SpanContext()
+	span.End()
+	return !spanCtx.IsValid()
+}
+
+func isExplicitConfig(cfg Config) bool {
+	if cfg.Endpoint != "" || cfg.Insecure {
+		return true
+	}
+	if cfg.ServiceName != "" && cfg.ServiceName != defaultServiceName {
+		return true
+	}
+	if cfg.Sampler != "" && cfg.Sampler != defaultSampler {
+		return true
+	}
+	return false
+}
+
 // SetupWithDefaults is a convenience function that accepts a service name.
 func SetupWithDefaults(ctx context.Context, serviceName string) (Shutdown, error) {
 	return Setup(ctx, Config{ServiceName: serviceName})

internal/otelx/otelx_otel_test.go

@@ -94,6 +94,28 @@ func TestSetup_RespectsExistingPropagator(t *testing.T) {
 	assert.Equal(t, customProp, otel.GetTextMapPropagator())
 }
 
+//nolint:paralleltest // Mutates global OTEL provider/propagator.
+func TestSetup_OverridesExistingProviderWhenConfigured(t *testing.T) {
+	prevProvider := otel.GetTracerProvider()
+	prevPropagator := otel.GetTextMapPropagator()
+	existing := trace.NewTracerProvider()
+	otel.SetTracerProvider(existing)
+	otel.SetTextMapPropagator(propagation.TraceContext{})
+	t.Cleanup(func() {
+		otel.SetTracerProvider(prevProvider)
+		otel.SetTextMapPropagator(prevPropagator)
+	})
+
+	shutdown, err := Setup(context.Background(), Config{
+		Endpoint: "http://127.0.0.1:4318",
+		Sampler:  "always_on",
+		Insecure: true,
+	})
+	require.NoError(t, err)
+	require.NotNil(t, shutdown)
+	assert.NotSame(t, existing, otel.GetTracerProvider())
+}
+
 //nolint:paralleltest // Mutates global OTEL provider/propagator.
 func TestSetup_InsecureEndpoint(t *testing.T) {
 	prevProvider := otel.GetTracerProvider()