add_mode processor for gateway

Author: rcastley

cmd/otelcol/config/collector/gateway_config.yaml

@@ -82,6 +82,13 @@ processors:
         #value: staging/production/...
         #key: deployment.environment
 
+  # The following processor is used to add "otelcol.service.mode" attribute to the internal metrics
+  resource/add_mode:
+    attributes:
+      - action: insert
+        value: "gateway"
+        key: otelcol.service.mode
+
   # Detect if the collector is running on a cloud system. Overrides resource attributes set by receivers.
   # Detector order is important: the `system` detector goes last so it can't preclude cloud detectors from setting host/os info.
   # https://github.com/open-telemetry/opentelemetry-collector-contrib/tree/main/processor/resourcedetectionprocessor#ordering
@@ -142,7 +149,7 @@ service:
       exporters: [signalfx]
     metrics/internal:
       receivers: [prometheus/internal]
-      processors: [memory_limiter, batch, resourcedetection/internal]
+      processors: [memory_limiter, batch, resourcedetection/internal, resource/add_mode]
       exporters: [signalfx/internal]
     logs/signalfx:
       receivers: [signalfx]