[exporter/datadog]: fix service name resolution (#570)

Author: ericmustin

Diff for: CHANGELOG.md

@@ -55,6 +55,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   ([#581](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/581))
 - `opentelemetry-instrumentation-botocore` Suppress botocore downstream instrumentation like urllib3
   ([#563](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/563))
+- `opentelemetry-exporter-datadog` Datadog exporter should not use `unknown_service` as fallback resource service name.
+  ([#570](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/570))
 
 ### Added
 - `opentelemetry-instrumentation-httpx` Add `httpx` instrumentation

Diff for: exporter/opentelemetry-exporter-datadog/src/opentelemetry/exporter/datadog/exporter.py

@@ -135,12 +135,12 @@ def _translate_to_datadog(self, spans):
             [
                 resource_tags,
                 resource_service_name,
-            ] = _extract_tags_from_resource(span.resource)
+            ] = _extract_tags_from_resource(span.resource, self.service)
 
             datadog_span = DatadogSpan(
                 tracer,
                 _get_span_name(span),
-                service=resource_service_name or self.service,
+                service=resource_service_name,
                 resource=_get_resource(span),
                 span_type=_get_span_type(span),
                 trace_id=trace_id,
@@ -312,19 +312,23 @@ def _parse_tags_str(tags_str):
     return parsed_tags
 
 
-def _extract_tags_from_resource(resource):
+def _extract_tags_from_resource(resource, fallback_service_name):
     """Parse tags from resource.attributes, except service.name which
     has special significance within datadog"""
     tags = {}
-    service_name = None
     if not (resource and getattr(resource, "attributes", None)):
-        return [tags, service_name]
+        return [tags, fallback_service_name]
 
+    service_name = None
     for attribute_key, attribute_value in resource.attributes.items():
         if attribute_key == SERVICE_NAME_TAG:
             service_name = attribute_value
         else:
             tags[attribute_key] = attribute_value
+
+    if service_name is None or service_name == "unknown_service":
+        service_name = fallback_service_name
+
     return [tags, service_name]
 
 

Diff for: exporter/opentelemetry-exporter-datadog/tests/test_datadog_exporter.py

@@ -612,3 +612,41 @@ def test_sampling_rate(self):
         ]
         expected = [0.5]
         self.assertListEqual(actual, expected)
+
+    def test_service_name_fallback(self):
+        context = trace_api.SpanContext(
+            trace_id=0x000000000000000000000000DEADBEEF,
+            span_id=0x34BF92DEEFC58C92,
+            is_remote=False,
+            trace_flags=trace_api.TraceFlags(trace_api.TraceFlags.SAMPLED),
+        )
+        trace_api.get_tracer_provider().sampler = sampling.TraceIdRatioBased(
+            0.5
+        )
+
+        resource_with_default_name = Resource(
+            attributes={
+                "key_resource": "some_resource",
+                "service.name": "unknown_service",
+            }
+        )
+
+        span = trace._Span(
+            name="sampled",
+            context=context,
+            parent=None,
+            resource=resource_with_default_name,
+        )
+        span.start()
+        span.end()
+
+        # pylint: disable=protected-access
+        exporter = datadog.DatadogSpanExporter(service="fallback_service_name")
+        datadog_spans = [
+            span.to_dict() for span in exporter._translate_to_datadog([span])
+        ]
+
+        self.assertEqual(len(datadog_spans), 1)
+
+        span = datadog_spans[0]
+        self.assertEqual(span["service"], "fallback_service_name")