feat(config): wire container resource detector via lazy contrib import

CHANGELOG.md

@@ -12,6 +12,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## Unreleased
 
+- `opentelemetry-sdk`: Add `container` resource detector support to declarative file configuration via `detection_development.detectors[].container`, using a lazy import of the `opentelemetry-resource-detector-containerid` contrib package
+  ([#5004](https://github.com/open-telemetry/opentelemetry-python/pull/5004))
 - `opentelemetry-sdk`: Add `create_resource` and `create_propagator`/`configure_propagator` to declarative file configuration, enabling Resource and propagator instantiation from config files without reading env vars
   ([#4979](https://github.com/open-telemetry/opentelemetry-python/pull/4979))
 - `opentelemetry-sdk`: Map Python `CRITICAL` log level to OTel `FATAL` severity text per the specification

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  # pylint: disable=import-outside-toplevel,no-name-in-module
+                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 +298,88 @@ 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):
+    @staticmethod
+    def _config_with_container() -> 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")