fix: disable metrics if using zipkin traces endpoint but empty metrics endpoint (#203)

* fix: disable metrics if using zipkin traces endpoint but empty metrics endpoint

* fix comment

Author: tim-mwangi

instrumentation/opentelemetry/init.go

@@ -390,7 +390,7 @@ func RegisterServiceWithSpanProcessorWrapper(serviceName string, resourceAttribu
 }
 
 func initializeMetrics(cfg *config.AgentConfig) func() {
-	if cfg.GetTelemetry() == nil || !cfg.GetTelemetry().GetMetricsEnabled().GetValue() {
+	if shouldDisableMetrics(cfg) {
 		return func() {}
 	}
 
@@ -428,6 +428,18 @@ func initializeMetrics(cfg *config.AgentConfig) func() {
 	}
 }
 
+func shouldDisableMetrics(cfg *config.AgentConfig) bool {
+	// Disable metrics if the tracing exporter is not OTLP(grpc) and the metrics endpoint is not explicitly set.
+	// This is because we use the traces OTLP endpoint for metrics if the metrics endpoint is not set.
+	// By default the traces endpoint is zipkin which does not have support for metrics.
+	if cfg.GetReporting() != nil && cfg.GetReporting().GetTraceReporterType() != config.TraceReporterType_OTLP &&
+		len(cfg.GetReporting().GetMetricEndpoint().GetValue()) == 0 {
+		return true
+	}
+
+	return cfg.GetTelemetry() == nil || !cfg.GetTelemetry().GetMetricsEnabled().GetValue()
+}
+
 // SpanProcessorWrapper wraps otel span processor
 // and is responsible to delegate calls to the wrapped processor
 type SpanProcessorWrapper interface {

instrumentation/opentelemetry/init_test.go

@@ -395,3 +395,22 @@ func TestInitWithSpanProcessorWrapper(t *testing.T) {
 	assert.Equal(t, 3, wrapper.onStartCount)
 	assert.Equal(t, 3, wrapper.onEndCount)
 }
+
+func TestShouldDisableMetrics(t *testing.T) {
+	// Using default values: since zipkin is the default traces exporter turn off metrics
+	cfg := config.Load()
+	assert.True(t, shouldDisableMetrics(cfg))
+
+	// For OTLP reporting endpoint, turn it on
+	cfg.Reporting.TraceReporterType = config.TraceReporterType_OTLP
+	assert.False(t, shouldDisableMetrics(cfg))
+
+	cfg = config.Load()
+	cfg.Telemetry.MetricsEnabled = config.Bool(false)
+	assert.True(t, shouldDisableMetrics(cfg))
+
+	// Set a metrics endpoint
+	cfg = config.Load()
+	cfg.Reporting.MetricEndpoint = config.String("localhost:4317")
+	assert.False(t, shouldDisableMetrics(cfg))
+}