tracing: fix Datadog span name

changelogs/current.yaml

@@ -183,6 +183,9 @@ bug_fixes:
 - area: redis
   change: |
     Fixed a bug where redis key with % in the key is failing with a validation error.
+- area: tracing
+  change: |
+    Fixed a bug in the Datadog tracer where Datadog's "operation name" field would contain what should be in the "resource name" field.
 - area: http
   change: |
     Close HTTP/2 and HTTP/3 connections that prematurely reset streams. The runtime key

source/extensions/tracers/datadog/tracer.cc

@@ -86,7 +86,12 @@ Tracing::SpanPtr Tracer::startSpan(const Tracing::Config&, Tracing::TraceContext
   // The OpenTracing implementation ignored the `Tracing::Config` argument,
   // so we will as well.
   datadog::tracing::SpanConfig span_config;
-  span_config.name = operation_name;
+  // The `operation_name` parameter to this function more closely matches
+  // Datadog's concept of "resource name." Datadog's "span name," or "operation
+  // name," instead describes the category of operation being performed, which
+  // here we hard-code.
+  span_config.name = "envoy.proxy";
+  span_config.resource = operation_name;
   span_config.start = estimateTime(stream_info.startTime());
 
   datadog::tracing::Tracer& tracer = *thread_local_tracer.tracer;

test/extensions/tracers/datadog/tracer_test.cc

@@ -116,9 +116,13 @@ TEST_F(DatadogTracerTest, SpanProperties) {
   ASSERT_TRUE(maybe_dd_span);
   const datadog::tracing::Span& dd_span = *maybe_dd_span;
 
-  // Verify that the span has the expected service name, operation name, start
-  // time, and sampling decision.
-  EXPECT_EQ("do.thing", dd_span.name());
+  // Verify that the span has the expected service name, operation name,
+  // resource name, start time, and sampling decision.
+  // Note that the `operation_name` we specified above becomes the
+  // `resource_name()` of the resulting Datadog span, while the Datadog span's
+  // `name()` (operation name) is hard-coded to "envoy.proxy."
+  EXPECT_EQ("envoy.proxy", dd_span.name());
+  EXPECT_EQ("do.thing", dd_span.resource_name());
   EXPECT_EQ("envoy", dd_span.service_name());
   ASSERT_TRUE(dd_span.trace_segment().sampling_decision());
   EXPECT_EQ(int(datadog::tracing::SamplingPriority::USER_DROP),