review default case for empty routing key

exporter/loadbalancingexporter/README.md

@@ -31,7 +31,9 @@ The options for `routing_key` are: `service`, `traceID`, `metric`, `resource`.
 
 **Important**: Don't use traceID in metric pipeline.
 
-If no `routing_key` is configured, the default routing mechanism is `traceID` . This means that spans belonging to the same `traceID` (or `service.name`, when `service` is used as the `routing_key`) will be sent to the same backend.
+If no `routing_key` is configured, the default routing mechanism is `traceID`  for traces, while `service` is the default for metrics. This means that spans belonging to the same `traceID` (or `service.name`, when `service` is used as the `routing_key`) will be sent to the same backend.
+
+If no routing_key is configured, the default routing mechanism is traceID for traces, while service is the default for metrics
 
 It requires a source of backend information to be provided: static, with a fixed list of backends, or DNS, with a hostname that will resolve to all IP addresses to use. The DNS resolver will periodically check for updates.
 

exporter/loadbalancingexporter/metrics_exporter.go

@@ -49,15 +49,13 @@ func newMetricsExporter(params exporter.CreateSettings, cfg component.Config) (*
 	metricExporter := metricExporterImp{loadBalancer: lb, routingKey: svcRouting}
 
 	switch cfg.(*Config).RoutingKey {
-	case "service": // , ""
+	case "service", "":
 		// default case for empty routing key
 		metricExporter.routingKey = svcRouting
 	case "resource":
 		metricExporter.routingKey = resourceRouting
 	case "metric":
 		metricExporter.routingKey = metricNameRouting
-	case "traceID", "":
-		fallthrough
 	default:
 		return nil, fmt.Errorf("unsupported routing_key: '%s'", cfg.(*Config).RoutingKey)
 	}