wire container resource detector in declarative config

When `resource.detection_development.detectors[].container` is set in
the config file, attempt to use `ContainerResourceDetector` from the
`opentelemetry-resource-detector-containerid` contrib package. Unlike
the process, host, and service detectors which are implemented in the
core SDK, container detection is not available in core. Rather than
adding a hard dependency on the contrib package, we use a lazy import:
if the package is installed it is used transparently; if absent a
warning is logged with an actionable install instruction.

This mirrors the approach taken by other SDKs: JS explicitly skips
container detection when no implementation is available, and PHP also
defers container detection to a contrib package.

See: open-telemetry/opentelemetry-configuration#570

Assisted-by: Claude Sonnet 4.6

Author: MikeGoldsmith

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

@@ -149,6 +149,28 @@ def _run_detectors(
     is updated in-place; later detectors overwrite earlier ones for the
     same key.
     """
+    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:
+        # https://github.com/open-telemetry/opentelemetry-configuration/issues/570
+        try:
+            from opentelemetry.resource.detector.containerid import (  # type: ignore[import-not-found]  # noqa: PLC0415
+                ContainerResourceDetector,
+            )
+
+            detected_attrs.update(
+                ContainerResourceDetector().detect().attributes
+            )
+        except ImportError:
+            _logger.warning(
+                "container resource detector requested but "
+                "'opentelemetry-resource-detector-containerid' is not "
+                "installed; install it to enable container detection"
+            )
 
 
 def _filter_attributes(

opentelemetry-sdk/tests/_configuration/test_resource.py

@@ -14,15 +14,18 @@
 
 import os
 import unittest
-from unittest.mock import patch
+from unittest.mock import MagicMock, patch
 
 from opentelemetry.sdk._configuration._resource import create_resource
 from opentelemetry.sdk._configuration.models import (
     AttributeNameValue,
     AttributeType,
+    ExperimentalResourceDetection,
+    ExperimentalResourceDetector,
 )
 from opentelemetry.sdk._configuration.models import Resource as ResourceConfig
 from opentelemetry.sdk.resources import (
+    CONTAINER_ID,
     SERVICE_NAME,
     TELEMETRY_SDK_LANGUAGE,
     TELEMETRY_SDK_NAME,
@@ -295,3 +298,87 @@ def test_attributes_list_invalid_pair_skipped(self):
         self.assertEqual(resource.attributes["foo"], "bar")
         self.assertNotIn("no-equals", resource.attributes)
         self.assertTrue(any("no-equals" in msg for msg in cm.output))
+
+
+class TestContainerResourceDetector(unittest.TestCase):
+    def _config_with_container(self) -> ResourceConfig:
+        return ResourceConfig(
+            detection_development=ExperimentalResourceDetection(
+                detectors=[ExperimentalResourceDetector(container={})]
+            )
+        )
+
+    def test_container_detector_not_run_when_absent(self):
+        resource = create_resource(ResourceConfig())
+        self.assertNotIn(CONTAINER_ID, resource.attributes)
+
+    def test_container_detector_not_run_when_detection_development_is_none(
+        self,
+    ):
+        resource = create_resource(ResourceConfig(detection_development=None))
+        self.assertNotIn(CONTAINER_ID, resource.attributes)
+
+    def test_container_detector_not_run_when_detectors_list_empty(self):
+        config = ResourceConfig(
+            detection_development=ExperimentalResourceDetection(detectors=[])
+        )
+        resource = create_resource(config)
+        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},
+        ):
+            with self.assertLogs(
+                "opentelemetry.sdk._configuration._resource", level="WARNING"
+            ) as cm:
+                resource = create_resource(self._config_with_container())
+        self.assertNotIn(CONTAINER_ID, resource.attributes)
+        self.assertTrue(
+            any(
+                "opentelemetry-resource-detector-containerid" in msg
+                for msg in cm.output
+            )
+        )
+
+    def test_container_detector_uses_contrib_when_available(self):
+        """When the contrib package is installed, 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
+
+        with patch.dict(
+            "sys.modules",
+            {"opentelemetry.resource.detector.containerid": mock_module},
+        ):
+            resource = create_resource(self._config_with_container())
+
+        self.assertEqual(resource.attributes[CONTAINER_ID], "abc123")
+
+    def test_explicit_attributes_override_container_detector(self):
+        """Config attributes win over detector-provided values."""
+        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
+
+        config = ResourceConfig(
+            attributes=[
+                AttributeNameValue(name="container.id", value="explicit-id")
+            ],
+            detection_development=ExperimentalResourceDetection(
+                detectors=[ExperimentalResourceDetector(container={})]
+            ),
+        )
+        with patch.dict(
+            "sys.modules",
+            {"opentelemetry.resource.detector.containerid": mock_module},
+        ):
+            resource = create_resource(config)
+
+        self.assertEqual(resource.attributes[CONTAINER_ID], "explicit-id")