feat(config): add host resource detector support for declarative config (#5002)

* config: add resource and propagator creation from declarative config

Implements create_resource() and create_propagator()/configure_propagator()
for the declarative file configuration. Resource creation does not read
OTEL_RESOURCE_ATTRIBUTES or run any detectors (matches Java/JS SDK behavior).
Propagator configuration always calls set_global_textmap to override Python's
default tracecontext+baggage, setting a noop CompositePropagator when no
propagator is configured.

Assisted-by: Claude Sonnet 4.6

* update changelog with PR number

Assisted-by: Claude Sonnet 4.6

* fix pylint, pyright and ruff errors in resource/propagator config

- _resource.py: refactor _coerce_attribute_value to dispatch table to
  avoid too-many-return-statements; fix short variable names k/v ->
  attr_key/attr_val; fix return type of _sdk_default_attributes to
  dict[str, str] to satisfy pyright
- _propagator.py: rename short variable names e -> exc, p -> propagator
- test_resource.py: move imports to top level; split TestCreateResource
  (25 methods) into three focused classes to satisfy too-many-public-methods
- test_propagator.py: add pylint disable for protected-access

Assisted-by: Claude Sonnet 4.6

* address review feedback: use _DEFAULT_RESOURCE, fix bool_array coercion

- replace _sdk_default_attributes() with _DEFAULT_RESOURCE from resources module
- move _coerce_bool into dispatch tables for both scalar and array bool types,
  fixing a bug where bool_array with string values like "false" would coerce
  incorrectly via plain bool() (non-empty string -> True)
- add test for bool_array with string values to cover the bug

Assisted-by: Claude Sonnet 4.6

* fix linter

* address review feedback: single coercion table, simplify attributes merge

- collapse _SCALAR_COERCIONS and _ARRAY_COERCIONS into a single _COERCIONS
  dict using an _array() factory, reducing _coerce_attribute_value to two lines
- process attributes_list before attributes so explicit attributes naturally
  overwrite list entries without needing an explicit guard

Assisted-by: Claude Sonnet 4.6

* use Callable type annotation on _array helper

Assisted-by: Claude Sonnet 4.6

* add detection infrastructure foundations for resource detectors

Adds _run_detectors() stub and _filter_attributes() to create_resource(),
providing the shared scaffolding for detector PRs to build on. Detectors
are opt-in: nothing runs unless explicitly listed under
detection_development.detectors in the config. The include/exclude
attribute filter mirrors other SDK behaviour.

Assisted-by: Claude Sonnet 4.6

* move service.name default into base resource

Merges service.name=unknown_service into base before running detectors,
so detectors (e.g. service) can override it. Previously it was added to
config_attrs and merged last, which would have silently overridden any
detector-provided service.name.

Assisted-by: Claude Sonnet 4.6

* remove unused logging import from _propagator.py

Assisted-by: Claude Sonnet 4.6

* wire host resource detector in declarative config

Makes _HostResourceDetector public as HostResourceDetector and wires
it to detection_development.detectors[].host in _run_detectors().

Assisted-by: Claude Sonnet 4.6

* add changelog entry for host resource detector (#5002)

Assisted-by: Claude Sonnet 4.6

* fix import sort in test_resources.py (ruff)

Assisted-by: Claude Sonnet 4.6

* revert HostResourceDetector to private _HostResourceDetector

Assisted-by: Claude Sonnet 4.6

* Apply suggestion from @xrmx

* Update test_resources.py

* Update _resource.py

---------

Co-authored-by: Aaron Abbott <aaronabbott@google.com>
Co-authored-by: Riccardo Magliocchetti <riccardo.magliocchetti@gmail.com>

Author: 3 people

CHANGELOG.md

@@ -12,6 +12,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## Unreleased
 
+- `opentelemetry-sdk`: Add `host` resource detector support to declarative file configuration via `detection_development.detectors[].host`
+  ([#5002](https://github.com/open-telemetry/opentelemetry-python/pull/5002))
 - `opentelemetry-sdk`: Add `container` resource detector support to declarative file configuration via `detection_development.detectors[].container`, using entry point loading of the `opentelemetry-resource-detector-containerid` contrib package
   ([#5004](https://github.com/open-telemetry/opentelemetry-python/pull/5004))
 - `opentelemetry-sdk`: Add `create_tracer_provider`/`configure_tracer_provider` to declarative file configuration, enabling TracerProvider instantiation from config files without reading env vars

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

@@ -31,6 +31,7 @@
     SERVICE_NAME,
     ProcessResourceDetector,
     Resource,
+    _HostResourceDetector,
 )
 from opentelemetry.util._importlib_metadata import entry_points
 
@@ -151,6 +152,9 @@ def _run_detectors(
     is updated in-place; later detectors overwrite earlier ones for the
     same key.
     """
+    if detector_config.host is not None:
+        detected_attrs.update(_HostResourceDetector().detect().attributes)
+
     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,
@@ -175,6 +179,7 @@ def _run_detectors(
             )
         else:
             detected_attrs.update(ep.load()().detect().attributes)
+
     if detector_config.process is not None:
         detected_attrs.update(ProcessResourceDetector().detect().attributes)
 

opentelemetry-sdk/tests/_configuration/test_resource.py

@@ -13,6 +13,7 @@
 # limitations under the License.
 
 import os
+import socket
 import sys
 import unittest
 from unittest.mock import MagicMock, patch
@@ -23,10 +24,13 @@
     AttributeType,
     ExperimentalResourceDetection,
     ExperimentalResourceDetector,
+    IncludeExclude,
 )
 from opentelemetry.sdk._configuration.models import Resource as ResourceConfig
 from opentelemetry.sdk.resources import (
     CONTAINER_ID,
+    HOST_ARCH,
+    HOST_NAME,
     PROCESS_PID,
     PROCESS_RUNTIME_NAME,
     SERVICE_NAME,
@@ -303,6 +307,77 @@ def test_attributes_list_invalid_pair_skipped(self):
         self.assertTrue(any("no-equals" in msg for msg in cm.output))
 
 
+class TestHostResourceDetector(unittest.TestCase):
+    @staticmethod
+    def _config_with_host() -> ResourceConfig:
+        return ResourceConfig(
+            detection_development=ExperimentalResourceDetection(
+                detectors=[ExperimentalResourceDetector(host={})]
+            )
+        )
+
+    def test_host_detector_adds_host_attributes(self):
+        resource = create_resource(self._config_with_host())
+        self.assertIn(HOST_NAME, resource.attributes)
+        self.assertEqual(resource.attributes[HOST_NAME], socket.gethostname())
+        self.assertIn(HOST_ARCH, resource.attributes)
+
+    def test_host_detector_also_includes_sdk_defaults(self):
+        resource = create_resource(self._config_with_host())
+        self.assertEqual(resource.attributes[TELEMETRY_SDK_LANGUAGE], "python")
+        self.assertIn(TELEMETRY_SDK_VERSION, resource.attributes)
+
+    def test_host_detector_not_run_when_absent(self):
+        resource = create_resource(ResourceConfig())
+        self.assertNotIn(HOST_NAME, resource.attributes)
+        self.assertNotIn(HOST_ARCH, resource.attributes)
+
+    def test_host_detector_not_run_when_detection_development_is_none(self):
+        resource = create_resource(ResourceConfig(detection_development=None))
+        self.assertNotIn(HOST_NAME, resource.attributes)
+
+    def test_host_detector_not_run_when_detectors_list_empty(self):
+        config = ResourceConfig(
+            detection_development=ExperimentalResourceDetection(detectors=[])
+        )
+        resource = create_resource(config)
+        self.assertNotIn(HOST_NAME, resource.attributes)
+
+    def test_explicit_attributes_override_host_detector(self):
+        config = ResourceConfig(
+            attributes=[
+                AttributeNameValue(name="host.name", value="custom-host")
+            ],
+            detection_development=ExperimentalResourceDetection(
+                detectors=[ExperimentalResourceDetector(host={})]
+            ),
+        )
+        resource = create_resource(config)
+        self.assertEqual(resource.attributes[HOST_NAME], "custom-host")
+
+    def test_included_filter_limits_host_attributes(self):
+        config = ResourceConfig(
+            detection_development=ExperimentalResourceDetection(
+                detectors=[ExperimentalResourceDetector(host={})],
+                attributes=IncludeExclude(included=["host.name"]),
+            )
+        )
+        resource = create_resource(config)
+        self.assertIn(HOST_NAME, resource.attributes)
+        self.assertNotIn(HOST_ARCH, resource.attributes)
+
+    def test_excluded_filter_removes_host_attributes(self):
+        config = ResourceConfig(
+            detection_development=ExperimentalResourceDetection(
+                detectors=[ExperimentalResourceDetector(host={})],
+                attributes=IncludeExclude(excluded=["host.name"]),
+            )
+        )
+        resource = create_resource(config)
+        self.assertNotIn(HOST_NAME, resource.attributes)
+        self.assertIn(HOST_ARCH, resource.attributes)
+
+
 class TestContainerResourceDetector(unittest.TestCase):
     @staticmethod
     def _config_with_container() -> ResourceConfig: