distro: set default sampler to parentbased_traceidratio (#351)

Author: xrmx

src/elasticotel/distro/__init__.py

@@ -35,6 +35,7 @@
     OTEL_EXPERIMENTAL_RESOURCE_DETECTORS,
     OTEL_EXPORTER_OTLP_METRICS_TEMPORALITY_PREFERENCE,
     OTEL_EXPORTER_OTLP_PROTOCOL,
+    OTEL_TRACES_SAMPLER,
 )
 from opentelemetry.sdk.resources import OTELResourceDetector
 from opentelemetry.util._importlib_metadata import EntryPoint
@@ -114,6 +115,7 @@ def _configure(self, **kwargs):
         os.environ.setdefault(OTEL_METRICS_EXEMPLAR_FILTER, "always_off")
         # preference to use DELTA temporality as we can handle only this kind of Histograms
         os.environ.setdefault(OTEL_EXPORTER_OTLP_METRICS_TEMPORALITY_PREFERENCE, "DELTA")
+        os.environ.setdefault(OTEL_TRACES_SAMPLER, "parentbased_traceidratio")
 
         base_resource_detectors = ["process_runtime", "os", "otel", "telemetry_distro", "service_instance"]
         detectors = base_resource_detectors + get_cloud_resource_detectors()

tests/distro/test_distro.py

@@ -32,7 +32,9 @@
     OTEL_EXPERIMENTAL_RESOURCE_DETECTORS,
     OTEL_EXPORTER_OTLP_METRICS_TEMPORALITY_PREFERENCE,
     OTEL_EXPORTER_OTLP_PROTOCOL,
+    OTEL_TRACES_SAMPLER,
 )
+from opentelemetry.sdk.trace import sampling
 from opentelemetry._opamp.proto import opamp_pb2 as opamp_pb2
 
 
@@ -51,6 +53,20 @@ def test_default_configuration(self):
         )
         self.assertEqual("always_off", os.environ.get(OTEL_METRICS_EXEMPLAR_FILTER))
         self.assertEqual("DELTA", os.environ.get(OTEL_EXPORTER_OTLP_METRICS_TEMPORALITY_PREFERENCE))
+        self.assertEqual("parentbased_traceidratio", os.environ.get(OTEL_TRACES_SAMPLER))
+
+    @mock.patch.dict("os.environ", {}, clear=True)
+    def test_sampler_configuration(self):
+        distro = ElasticOpenTelemetryDistro()
+        distro._configure()
+        parent_sampler = sampling._get_from_env_or_default()
+
+        assert isinstance(parent_sampler, sampling.ParentBasedTraceIdRatio)
+
+        sampler = parent_sampler._root
+
+        assert isinstance(sampler, sampling.TraceIdRatioBased)
+        assert sampler.rate == 1.0
 
     @mock.patch.dict("os.environ", {}, clear=True)
     def test_load_instrumentor_call_with_default_kwargs_for_SystemMetricsInstrumentor(self):