feat(config): add pull metric reader support to declarative config

.changelog/5216.added

@@ -0,0 +1 @@
+`opentelemetry-sdk`: add pull metric reader support to declarative file configuration, including Prometheus metric reader via the `prometheus_development` config field

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

@@ -21,6 +21,9 @@
 from opentelemetry.sdk._configuration.models import (
     ExemplarFilter as ExemplarFilterConfig,
 )
+from opentelemetry.sdk._configuration.models import (
+    ExperimentalPrometheusMetricExporter as PrometheusMetricExporterConfig,
+)
 from opentelemetry.sdk._configuration.models import (
     ExporterDefaultHistogramAggregation,
     ExporterTemporalityPreference,
@@ -41,6 +44,12 @@
 from opentelemetry.sdk._configuration.models import (
     PeriodicMetricReader as PeriodicMetricReaderConfig,
 )
+from opentelemetry.sdk._configuration.models import (
+    PullMetricExporter as PullMetricExporterConfig,
+)
+from opentelemetry.sdk._configuration.models import (
+    PullMetricReader as PullMetricReaderConfig,
+)
 from opentelemetry.sdk._configuration.models import (
     PushMetricExporter as PushMetricExporterConfig,
 )
@@ -392,18 +401,107 @@ def _create_periodic_metric_reader(
     )
 
 
+def _create_prometheus_metric_reader(
+    config: PrometheusMetricExporterConfig,
+) -> MetricReader:
+    """Create a PrometheusMetricReader from config.
+
+    Dynamically imports the prometheus exporter package to avoid a hard
+    dependency. Maps config fields to constructor parameters and starts
+    the HTTP server.
+    """
+    try:
+        # pylint: disable=import-outside-toplevel,no-name-in-module
+        from opentelemetry.exporter.prometheus import (  # type: ignore[import-untyped]  # noqa: PLC0415
+            PrometheusMetricReader,
+            start_http_server,
+        )
+    except ImportError as exc:
+        raise ConfigurationError(
+            "prometheus pull metric exporter requires "
+            "'opentelemetry-exporter-prometheus'. "
+            "Install it with: pip install opentelemetry-exporter-prometheus"
+        ) from exc
+
+    disable_target_info = bool(config.without_target_info_development)
+
+    if config.without_scope_info is not None:
+        _logger.warning(
+            "without_scope_info is not yet supported for "
+            "Prometheus metric exporter and will be ignored."
+        )
+    if config.with_resource_constant_labels is not None:
+        _logger.warning(
+            "with_resource_constant_labels is not yet supported for "
+            "Prometheus metric exporter and will be ignored."
+        )
+
+    reader = PrometheusMetricReader(
+        disable_target_info=disable_target_info,
+    )
+
+    port = config.port if config.port is not None else 9464
+    host = config.host if config.host is not None else "localhost"
+    start_http_server(port=port, addr=host)
+
+    return reader
+
+
+def _create_pull_metric_exporter(
+    config: PullMetricExporterConfig,
+) -> MetricReader:
+    """Create a pull metric exporter (which is itself a MetricReader) from config.
+
+    Pull metric exporters like Prometheus are combined reader+exporter objects:
+    the "exporter" IS the reader. The config schema models them as separate
+    exporter configs, but the factory returns a MetricReader.
+
+    Plugin pull exporters are loaded via the ``opentelemetry_pull_metric_exporter``
+    entry point group.
+    """
+    if config.prometheus_development is not None:
+        return _create_prometheus_metric_reader(config.prometheus_development)
+    if config.additional_properties:
+        name, plugin_config = next(iter(config.additional_properties.items()))
+        return load_entry_point("opentelemetry_pull_metric_exporter", name)(
+            **(plugin_config or {})
+        )
+    raise ConfigurationError(
+        "No exporter type specified in pull metric exporter config. "
+        "Supported types: prometheus_development."
+    )
+
+
+def _create_pull_metric_reader(
+    config: PullMetricReaderConfig,
+) -> MetricReader:
+    """Create a pull MetricReader from config.
+
+    The pull reader's exporter is itself a MetricReader (combined reader+exporter).
+    producers and cardinality_limits are not yet supported.
+    """
+    if config.producers:
+        _logger.warning(
+            "MetricProducer configuration is not yet supported for "
+            "pull metric readers and will be ignored."
+        )
+    if config.cardinality_limits is not None:
+        _logger.warning(
+            "cardinality_limits is not yet supported for "
+            "pull metric readers and will be ignored."
+        )
+    return _create_pull_metric_exporter(config.exporter)
+
+
 def _create_metric_reader(config: MetricReaderConfig) -> MetricReader:
     """Create a MetricReader from config."""
     if config.periodic is not None:
         return _create_periodic_metric_reader(config.periodic)
     if config.pull is not None:
-        raise ConfigurationError(
-            "Pull metric readers (e.g. Prometheus) are experimental and not yet supported "
-            "by declarative config. Use the SDK API directly to configure pull readers."
-        )
+        return _create_pull_metric_reader(config.pull)
     raise ConfigurationError(
         "No reader type specified in metric reader config. "
-        "Supported types: periodic."
+        "Supported types: periodic, pull."
     )
 
 

opentelemetry-sdk/tests/_configuration/test_meter_provider.py

@@ -26,6 +26,9 @@
 from opentelemetry.sdk._configuration.models import (
     ExemplarFilter as ExemplarFilterConfig,
 )
+from opentelemetry.sdk._configuration.models import (
+    ExperimentalPrometheusMetricExporter as PrometheusMetricExporterConfig,
+)
 from opentelemetry.sdk._configuration.models import (
     ExplicitBucketHistogramAggregation as ExplicitBucketConfig,
 )
@@ -52,6 +55,12 @@
 from opentelemetry.sdk._configuration.models import (
     PeriodicMetricReader as PeriodicMetricReaderConfig,
 )
+from opentelemetry.sdk._configuration.models import (
+    PullMetricExporter as PullMetricExporterConfig,
+)
+from opentelemetry.sdk._configuration.models import (
+    PullMetricReader as PullMetricReaderConfig,
+)
 from opentelemetry.sdk._configuration.models import (
     PushMetricExporter as PushMetricExporterConfig,
 )
@@ -306,13 +315,216 @@ def test_otlp_grpc_missing_package_raises(self):
                 create_meter_provider(config)
         self.assertIn("otlp-proto-grpc", str(ctx.exception))
 
-    def test_pull_reader_raises(self):
+
+class TestCreatePullMetricReaders(unittest.TestCase):
+    def test_pull_prometheus_creates_reader(self):
+        mock_reader_cls = MagicMock()
+        mock_start_server = MagicMock()
+        mock_module = MagicMock()
+        mock_module.PrometheusMetricReader = mock_reader_cls
+        mock_module.start_http_server = mock_start_server
+
+        with patch.dict(
+            sys.modules,
+            {"opentelemetry.exporter.prometheus": mock_module},
+        ):
+            config = MeterProviderConfig(
+                readers=[
+                    MetricReaderConfig(
+                        pull=PullMetricReaderConfig(
+                            exporter=PullMetricExporterConfig(
+                                prometheus_development=PrometheusMetricExporterConfig(
+                                    host="0.0.0.0",
+                                    port=9090,
+                                    without_target_info_development=True,
+                                )
+                            )
+                        )
+                    )
+                ]
+            )
+            provider = create_meter_provider(config)
+
+        mock_reader_cls.assert_called_once_with(disable_target_info=True)
+        mock_start_server.assert_called_once_with(port=9090, addr="0.0.0.0")
+        self.assertEqual(len(provider._sdk_config.metric_readers), 1)
+
+    def test_pull_prometheus_defaults(self):
+        mock_reader_cls = MagicMock()
+        mock_start_server = MagicMock()
+        mock_module = MagicMock()
+        mock_module.PrometheusMetricReader = mock_reader_cls
+        mock_module.start_http_server = mock_start_server
+
+        with patch.dict(
+            sys.modules,
+            {"opentelemetry.exporter.prometheus": mock_module},
+        ):
+            config = MeterProviderConfig(
+                readers=[
+                    MetricReaderConfig(
+                        pull=PullMetricReaderConfig(
+                            exporter=PullMetricExporterConfig(
+                                prometheus_development=PrometheusMetricExporterConfig()
+                            )
+                        )
+                    )
+                ]
+            )
+            provider = create_meter_provider(config)
+
+        mock_reader_cls.assert_called_once_with(disable_target_info=False)
+        mock_start_server.assert_called_once_with(port=9464, addr="localhost")
+        self.assertEqual(len(provider._sdk_config.metric_readers), 1)
+
+    def test_pull_prometheus_missing_package_raises(self):
+        with patch.dict(
+            sys.modules,
+            {"opentelemetry.exporter.prometheus": None},
+        ):
+            config = MeterProviderConfig(
+                readers=[
+                    MetricReaderConfig(
+                        pull=PullMetricReaderConfig(
+                            exporter=PullMetricExporterConfig(
+                                prometheus_development=PrometheusMetricExporterConfig()
+                            )
+                        )
+                    )
+                ]
+            )
+            with self.assertRaises(ConfigurationError):
+                create_meter_provider(config)
+
+    def test_pull_no_exporter_raises(self):
         config = MeterProviderConfig(
-            readers=[MetricReaderConfig(pull=MagicMock())]
+            readers=[
+                MetricReaderConfig(
+                    pull=PullMetricReaderConfig(
+                        exporter=PullMetricExporterConfig()
+                    )
+                )
+            ]
         )
         with self.assertRaises(ConfigurationError):
             create_meter_provider(config)
 
+    def test_pull_plugin_loads_via_entry_point(self):
+        mock_reader = MagicMock()
+        mock_class = MagicMock(return_value=mock_reader)
+        mock_entry_points = MagicMock(
+            return_value=[MagicMock(**{"load.return_value": mock_class})]
+        )
+        with patch(
+            "opentelemetry.sdk._configuration._common.entry_points",
+            mock_entry_points,
+        ):
+            config = MeterProviderConfig(
+                readers=[
+                    MetricReaderConfig(
+                        pull=PullMetricReaderConfig(
+                            # pylint: disable=unexpected-keyword-arg
+                            exporter=PullMetricExporterConfig(
+                                my_custom_reader={"port": 8080}
+                            )
+                        )
+                    )
+                ]
+            )
+            provider = create_meter_provider(config)
+        self.assertEqual(len(provider._sdk_config.metric_readers), 1)
+        mock_class.assert_called_once_with(port=8080)
+        mock_entry_points.assert_called_once_with(
+            group="opentelemetry_pull_metric_exporter",
+            name="my_custom_reader",
+        )
+
+    def test_pull_plugin_not_found_raises(self):
+        with patch(
+            "opentelemetry.sdk._configuration._common.entry_points",
+            return_value=[],
+        ):
+            config = MeterProviderConfig(
+                readers=[
+                    MetricReaderConfig(
+                        pull=PullMetricReaderConfig(
+                            # pylint: disable=unexpected-keyword-arg
+                            exporter=PullMetricExporterConfig(
+                                no_such_reader={}
+                            )
+                        )
+                    )
+                ]
+            )
+            with self.assertRaises(ConfigurationError):
+                create_meter_provider(config)
+
+    def test_pull_producers_warns(self):
+        mock_module = MagicMock()
+
+        with patch.dict(
+            sys.modules,
+            {"opentelemetry.exporter.prometheus": mock_module},
+        ):
+            config = MeterProviderConfig(
+                readers=[
+                    MetricReaderConfig(
+                        pull=PullMetricReaderConfig(
+                            exporter=PullMetricExporterConfig(
+                                prometheus_development=PrometheusMetricExporterConfig()
+                            ),
+                            producers=[MagicMock()],
+                        )
+                    )
+                ]
+            )
+            with self.assertLogs(
+                "opentelemetry.sdk._configuration._meter_provider",
+                level="WARNING",
+            ) as cm:
+                create_meter_provider(config)
+        self.assertTrue(any("MetricProducer" in msg for msg in cm.output))
+
+    def test_pull_cardinality_limits_warns(self):
+        mock_module = MagicMock()
+
+        with patch.dict(
+            sys.modules,
+            {"opentelemetry.exporter.prometheus": mock_module},
+        ):
+            config = MeterProviderConfig(
+                readers=[
+                    MetricReaderConfig(
+                        pull=PullMetricReaderConfig(
+                            exporter=PullMetricExporterConfig(
+                                prometheus_development=PrometheusMetricExporterConfig()
+                            ),
+                            cardinality_limits=MagicMock(),
+                        )
+                    )
+                ]
+            )
+            with self.assertLogs(
+                "opentelemetry.sdk._configuration._meter_provider",
+                level="WARNING",
+            ) as cm:
+                create_meter_provider(config)
+        self.assertTrue(any("cardinality_limits" in msg for msg in cm.output))
+
+
+class TestCreateMetricReadersGeneral(unittest.TestCase):
+    @staticmethod
+    def _make_periodic_config(exporter_config):
+        return MeterProviderConfig(
+            readers=[
+                MetricReaderConfig(
+                    periodic=PeriodicMetricReaderConfig(
+                        exporter=exporter_config
+                    )
+                )
+            ]
+        )
+
     def test_no_reader_type_raises(self):
         config = MeterProviderConfig(readers=[MetricReaderConfig()])
         with self.assertRaises(ConfigurationError):