load container detector via entry point instead of lazy import

Matches the env-var config counterpart (OTEL_EXPERIMENTAL_RESOURCE_DETECTORS)
and avoids a hard import dependency on the contrib package. Tests updated
to mock entry_points instead of sys.modules.

Assisted-by: Claude Sonnet 4.6

Author: MikeGoldsmith

opentelemetry-sdk/src/opentelemetry/sdk/_configuration/_resource.py

@@ -31,6 +31,7 @@
     SERVICE_NAME,
     Resource,
 )
+from opentelemetry.util._importlib_metadata import entry_points
 
 _logger = logging.getLogger(__name__)
 
@@ -151,26 +152,28 @@ def _run_detectors(
     """
     if detector_config.container is not None:
         # The container detector is not part of the core SDK. It is provided
-        # by the opentelemetry-resource-detector-containerid contrib package.
-        # We attempt a lazy import so the core SDK has no hard dependency on
-        # contrib; if the package is absent we log an actionable warning rather
-        # than raising an error. Other SDKs (e.g. JS) similarly skip container
-        # detection when no implementation is available. See also:
+        # by the opentelemetry-resource-detector-containerid contrib package,
+        # which registers itself under the opentelemetry_resource_detector
+        # entry point group as "container". Loading via entry point matches
+        # the env-var config counterpart (OTEL_EXPERIMENTAL_RESOURCE_DETECTORS)
+        # and avoids a hard import dependency on contrib. See also:
         # https://github.com/open-telemetry/opentelemetry-configuration/issues/570
-        try:
-            from opentelemetry.resource.detector.containerid import (  # type: ignore[import-not-found]  # noqa: PLC0415  # pylint: disable=import-outside-toplevel,no-name-in-module
-                ContainerResourceDetector,
-            )
-
-            detected_attrs.update(
-                ContainerResourceDetector().detect().attributes
-            )
-        except ImportError:
+        ep = next(
+            iter(
+                entry_points(
+                    group="opentelemetry_resource_detector", name="container"
+                )
+            ),
+            None,
+        )
+        if ep is None:
             _logger.warning(
                 "container resource detector requested but "
                 "'opentelemetry-resource-detector-containerid' is not "
                 "installed; install it to enable container detection"
             )
+        else:
+            detected_attrs.update(ep.load()().detect().attributes)
 
 
 def _filter_attributes(

opentelemetry-sdk/tests/_configuration/test_resource.py

@@ -327,10 +327,10 @@ def test_container_detector_not_run_when_detectors_list_empty(self):
         self.assertNotIn(CONTAINER_ID, resource.attributes)
 
     def test_container_detector_warns_when_package_missing(self):
-        """A warning is logged when the contrib package is not installed."""
-        with patch.dict(
-            "sys.modules",
-            {"opentelemetry.resource.detector.containerid": None},
+        """A warning is logged when the contrib entry point is not found."""
+        with patch(
+            "opentelemetry.sdk._configuration._resource.entry_points",
+            return_value=[],
         ):
             with self.assertLogs(
                 "opentelemetry.sdk._configuration._resource", level="WARNING"
@@ -345,16 +345,16 @@ def test_container_detector_warns_when_package_missing(self):
         )
 
     def test_container_detector_uses_contrib_when_available(self):
-        """When the contrib package is installed, container.id is detected."""
+        """When the contrib entry point is registered, container.id is detected."""
         mock_resource = Resource({CONTAINER_ID: "abc123"})
         mock_detector = MagicMock()
         mock_detector.return_value.detect.return_value = mock_resource
-        mock_module = MagicMock()
-        mock_module.ContainerResourceDetector = mock_detector
+        mock_ep = MagicMock()
+        mock_ep.load.return_value = mock_detector
 
-        with patch.dict(
-            "sys.modules",
-            {"opentelemetry.resource.detector.containerid": mock_module},
+        with patch(
+            "opentelemetry.sdk._configuration._resource.entry_points",
+            return_value=[mock_ep],
         ):
             resource = create_resource(self._config_with_container())
 
@@ -365,8 +365,8 @@ def test_explicit_attributes_override_container_detector(self):
         mock_resource = Resource({CONTAINER_ID: "detected-id"})
         mock_detector = MagicMock()
         mock_detector.return_value.detect.return_value = mock_resource
-        mock_module = MagicMock()
-        mock_module.ContainerResourceDetector = mock_detector
+        mock_ep = MagicMock()
+        mock_ep.load.return_value = mock_detector
 
         config = ResourceConfig(
             attributes=[
@@ -376,9 +376,9 @@ def test_explicit_attributes_override_container_detector(self):
                 detectors=[ExperimentalResourceDetector(container={})]
             ),
         )
-        with patch.dict(
-            "sys.modules",
-            {"opentelemetry.resource.detector.containerid": mock_module},
+        with patch(
+            "opentelemetry.sdk._configuration._resource.entry_points",
+            return_value=[mock_ep],
         ):
             resource = create_resource(config)