Tag federation request spans with the worker name

changelog.d/15042.feature

@@ -0,0 +1 @@
+Tag opentracing spans for federation requests with the name of the worker serving the request.

synapse/api/auth.py

@@ -32,7 +32,6 @@
 from synapse.http import get_request_user_agent
 from synapse.http.site import SynapseRequest
 from synapse.logging.opentracing import (
-    SynapseTags,
     active_span,
     force_tracing,
     start_active_span,
@@ -162,12 +161,6 @@ async def get_user_by_req(
                 parent_span.set_tag(
                     "authenticated_entity", requester.authenticated_entity
                 )
-                # We tag the Synapse instance name so that it's an easy jumping
-                # off point into the logs. Can also be used to filter for an
-                # instance that is under load.
-                parent_span.set_tag(
-                    SynapseTags.INSTANCE_NAME, self.hs.get_instance_name()
-                )
                 parent_span.set_tag("user_id", requester.user.to_string())
                 if requester.device_id is not None:
                     parent_span.set_tag("device_id", requester.device_id)

synapse/logging/opentracing.py

@@ -466,8 +466,16 @@ def init_tracer(hs: "HomeServer") -> None:
         STRIP_INSTANCE_NUMBER_SUFFIX_REGEX, "", hs.get_instance_name()
     )
 
+    jaeger_config = hs.config.tracing.jaeger_config
+    tags = jaeger_config.setdefault("tags", {})
+
+    # tag the Synapse instance name so that it's an easy jumping
+    # off point into the logs. Can also be used to filter for an
+    # instance that is under load.
+    tags.setdefault(SynapseTags.INSTANCE_NAME, hs.get_instance_name())
+
     config = JaegerConfig(
-        config=hs.config.tracing.jaeger_config,
+        config=jaeger_config,
         service_name=f"{hs.config.server.server_name} {instance_name_by_type}",
         scope_manager=LogContextScopeManager(),
         metrics_factory=PrometheusMetricsFactory(),