Make opentelemetry_metrics_exporter entrypoint support pull exporte…

…rs (#3428)

CHANGELOG.md

@@ -11,7 +11,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   ([#3335](https://github.com/open-telemetry/opentelemetry-python/pull/3335))
 - Fix error when no LoggerProvider configured for LoggingHandler
   ([#3423](https://github.com/open-telemetry/opentelemetry-python/pull/3423))
-
+- Make `opentelemetry_metrics_exporter` entrypoint support pull exporters
+  ([#3428](https://github.com/open-telemetry/opentelemetry-python/pull/3428))
 
 ## Version 1.20.0/0.41b0 (2023-09-04)
 

opentelemetry-api/src/opentelemetry/environment_variables.py

@@ -22,6 +22,29 @@
 """
 .. envvar:: OTEL_METRICS_EXPORTER
 
+Specifies which exporter is used for metrics. See `General SDK Configuration
+<https://opentelemetry.io/docs/concepts/sdk-configuration/general-sdk-configuration/#otel_metrics_exporter>`_.
+
+**Default value:** ``"otlp"``
+
+**Example:**
+
+``export OTEL_METRICS_EXPORTER="prometheus"``
+
+Accepted values for ``OTEL_METRICS_EXPORTER`` are:
+
+- ``"otlp"``
+- ``"prometheus"``
+- ``"none"``: No automatically configured exporter for metrics.
+
+.. note::
+
+    Exporter packages may add entry points for group ``opentelemetry_metrics_exporter`` which
+    can then be used with this environment variable by name. The entry point should point to
+    either a `opentelemetry.sdk.metrics.export.MetricExporter` (push exporter) or
+    `opentelemetry.sdk.metrics.export.MetricReader` (pull exporter) subclass; it must be
+    constructable without any required arguments. This mechanism is considered experimental and
+    may change in subsequent releases.
 """
 
 OTEL_PROPAGATORS = "OTEL_PROPAGATORS"

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

@@ -21,7 +21,7 @@
 import os
 from abc import ABC, abstractmethod
 from os import environ
-from typing import Callable, Dict, List, Optional, Sequence, Tuple, Type
+from typing import Callable, Dict, List, Optional, Sequence, Tuple, Type, Union
 
 from typing_extensions import Literal
 
@@ -47,6 +47,7 @@
 from opentelemetry.sdk.metrics import MeterProvider
 from opentelemetry.sdk.metrics.export import (
     MetricExporter,
+    MetricReader,
     PeriodicExportingMetricReader,
 )
 from opentelemetry.sdk.resources import Resource
@@ -210,16 +211,24 @@ def _init_tracing(
 
 
 def _init_metrics(
-    exporters: Dict[str, Type[MetricExporter]],
+    exporters_or_readers: Dict[
+        str, Union[Type[MetricExporter], Type[MetricReader]]
+    ],
     resource: Resource = None,
 ):
     metric_readers = []
 
-    for _, exporter_class in exporters.items():
+    for _, exporter_or_reader_class in exporters_or_readers.items():
         exporter_args = {}
-        metric_readers.append(
-            PeriodicExportingMetricReader(exporter_class(**exporter_args))
-        )
+
+        if issubclass(exporter_or_reader_class, MetricReader):
+            metric_readers.append(exporter_or_reader_class(**exporter_args))
+        else:
+            metric_readers.append(
+                PeriodicExportingMetricReader(
+                    exporter_or_reader_class(**exporter_args)
+                )
+            )
 
     provider = MeterProvider(resource=resource, metric_readers=metric_readers)
     set_meter_provider(provider)
@@ -249,7 +258,7 @@ def _import_exporters(
     log_exporter_names: Sequence[str],
 ) -> Tuple[
     Dict[str, Type[SpanExporter]],
-    Dict[str, Type[MetricExporter]],
+    Dict[str, Union[Type[MetricExporter], Type[MetricReader]]],
     Dict[str, Type[LogExporter]],
 ]:
     trace_exporters = {}
@@ -267,7 +276,9 @@ def _import_exporters(
     for (exporter_name, exporter_impl,) in _import_config_components(
         metric_exporter_names, "opentelemetry_metrics_exporter"
     ):
-        if issubclass(exporter_impl, MetricExporter):
+        # The metric exporter components may be push MetricExporter or pull exporters which
+        # subclass MetricReader directly
+        if issubclass(exporter_impl, (MetricExporter, MetricReader)):
             metric_exporters[exporter_name] = exporter_impl
         else:
             raise RuntimeError(f"{exporter_name} is not a metric exporter")

opentelemetry-sdk/tests/test_configurator.py

@@ -18,7 +18,7 @@
 from os import environ
 from typing import Dict, Iterable, Optional, Sequence
 from unittest import TestCase
-from unittest.mock import patch
+from unittest.mock import Mock, patch
 
 from pytest import raises
 
@@ -158,6 +158,20 @@ def shutdown(self, timeout_millis: float = 30_000, **kwargs) -> None:
         return True
 
 
+# MetricReader that can be configured as a pull exporter
+class DummyMetricReaderPullExporter(MetricReader):
+    def _receive_metrics(
+        self,
+        metrics: Iterable[Metric],
+        timeout_millis: float = 10_000,
+        **kwargs,
+    ) -> None:
+        pass
+
+    def shutdown(self, timeout_millis: float = 30_000, **kwargs) -> None:
+        return True
+
+
 class DummyOTLPMetricExporter:
     def __init__(self, *args, **kwargs):
         self.export_called = False
@@ -309,7 +323,6 @@ def tearDown(self):
         environ, {"OTEL_RESOURCE_ATTRIBUTES": "service.name=my-test-service"}
     )
     def test_trace_init_default(self):
-
         auto_resource = Resource.create(
             {
                 "telemetry.auto.version": "test-version",
@@ -740,6 +753,18 @@ def test_metrics_init_exporter(self):
         self.assertIsInstance(reader, DummyMetricReader)
         self.assertIsInstance(reader.exporter, DummyOTLPMetricExporter)
 
+    def test_metrics_init_pull_exporter(self):
+        resource = Resource.create({})
+        _init_metrics(
+            {"dummy_metric_reader": DummyMetricReaderPullExporter},
+            resource=resource,
+        )
+        self.assertEqual(self.set_provider_mock.call_count, 1)
+        provider = self.set_provider_mock.call_args[0][0]
+        self.assertIsInstance(provider, DummyMeterProvider)
+        reader = provider._sdk_config.metric_readers[0]
+        self.assertIsInstance(reader, DummyMetricReaderPullExporter)
+
 
 class TestExporterNames(TestCase):
     @patch.dict(
@@ -835,6 +860,28 @@ def test_console_exporters(self):
             ConsoleMetricExporter.__class__,
         )
 
+    @patch(
+        "opentelemetry.sdk._configuration.entry_points",
+    )
+    def test_metric_pull_exporter(self, mock_entry_points: Mock):
+        def mock_entry_points_impl(group, name):
+            if name == "dummy_pull_exporter":
+                return [
+                    IterEntryPoint(
+                        name=name, class_type=DummyMetricReaderPullExporter
+                    )
+                ]
+            return []
+
+        mock_entry_points.side_effect = mock_entry_points_impl
+        _, metric_exporters, _ = _import_exporters(
+            [], ["dummy_pull_exporter"], []
+        )
+        self.assertIs(
+            metric_exporters["dummy_pull_exporter"],
+            DummyMetricReaderPullExporter,
+        )
+
 
 class TestImportConfigComponents(TestCase):
     @patch(