Don't accept routing keys for metrics.

component/otelcol/exporter/loadbalancing/loadbalancing.go

@@ -2,6 +2,7 @@
 package loadbalancing
 
 import (
+	"fmt"
 	"time"
 
 	"github.com/alecthomas/units"
@@ -48,6 +49,7 @@ type Arguments struct {
 var (
 	_ exporter.Arguments = Arguments{}
 	_ river.Defaulter    = &Arguments{}
+	_ river.Validator    = &Arguments{}
 )
 
 var (
@@ -72,6 +74,22 @@ func (args *Arguments) SetToDefault() {
 	*args = DefaultArguments
 }
 
+// Validate implements river.Validator.
+func (args *Arguments) Validate() error {
+	//TODO(ptodev): Add support for "resource" and "metric" routing keys later.
+	// The reason we can't add them yet is that otelcol.exporter.loadbalancing
+	// is labeled as "beta", but those routing keys are experimental.
+	// We need a way to label otelcol.exporter.loadbalancing as "beta"
+	// for logs and traces, but "experimental" for metrics.
+	switch args.RoutingKey {
+	case "service", "traceID":
+		// The routing key is valid.
+	default:
+		return fmt.Errorf("invalid routing key %q", args.RoutingKey)
+	}
+	return nil
+}
+
 // Convert implements exporter.Arguments.
 func (args Arguments) Convert() (otelcomponent.Config, error) {
 	return &loadbalancingexporter.Config{

docs/sources/flow/reference/components/otelcol.exporter.loadbalancing.md

@@ -65,20 +65,10 @@ Name | Type | Description | Default | Required
 `routing_key` | `string` | Routing strategy for load balancing. | `"traceID"` | no
 
 The `routing_key` attribute determines how to route signals across endpoints. Its value could be one of the following:
-* `"service"`:
-  * Works for logs, spans, and metrics. 
-  * Signals with the same `service.name` will be exported to the same backend.
-    This is useful when using processors like the span metrics, so all spans for each service are sent to consistent Agent instances 
-    for metric collection. Otherwise, metrics for the same services would be sent to different Agents, making aggregations inaccurate.
-* `"traceID"`: 
-  * Works for logs and spans.
-  * Signals belonging to the same traceID will be exported to the same backend.
-* `"resource"`:  
-  * Works for metrics.
-  * Signals with the same metric name and the same resource attributes will be exported to the same backend.
-* `"metric"`:   
-  * Works for metrics.
-  * Signals with the same metric name will be exported to the same backend.
+* `"service"`: spans with the same `service.name` will be exported to the same backend.
+This is useful when using processors like the span metrics, so all spans for each service are sent to consistent Agent instances 
+for metric collection. Otherwise, metrics for the same services would be sent to different Agents, making aggregations inaccurate.
+* `"traceID"`: spans belonging to the same traceID will be exported to the same backend.
 
 ## Blocks