Load instrumentors via Distro

This commit makes the following changes:

- Introduces a new `load_instrumentor(EntryPoint) -> None:` with a
default implementation method to the `BaseDistro` class.
- The default implementation loads the insrumentor from the provided
entry point and calls applies it without any arguments. (same as before)
- sitecustomize now calls Distro's `load_instrumentor` method to load
and activate an instrumentor instead of doing it directly.
- Added a new `DefaultDistro` implementation which is used if not distro
is found by entry points.

CHANGELOG.md

@@ -9,6 +9,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Changed
 - `opentelemetry-propagator-ot-trace` Use `TraceFlags` object in `extract`
   ([#472](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/472))
+- Distros can now implement `load_instrumentor(EntryPoint)` method to customize instrumentor
+  loading behaviour.
+  ([#480](https://github.com/open-telemetry/opentelemetry-python/pull/480))
 
 ### Added
 - Move `opentelemetry-instrumentation` from core repository

opentelemetry-instrumentation/src/opentelemetry/instrumentation/auto_instrumentation/sitecustomize.py

@@ -23,37 +23,49 @@
 from opentelemetry.environment_variables import (
     OTEL_PYTHON_DISABLED_INSTRUMENTATIONS,
 )
+from opentelemetry.instrumentation.distro import BaseDistro, DefaultDistro
 
 logger = getLogger(__file__)
 
 
-def _load_distros():
+def _load_distros() -> BaseDistro:
     for entry_point in iter_entry_points("opentelemetry_distro"):
         try:
-            entry_point.load()().configure()  # type: ignore
-            logger.debug("Distribution %s configured", entry_point.name)
+            distro = entry_point.load()()
+            if not isinstance(distro, BaseDistro):
+                logger.debug(
+                    "%s is not an OpenTelemetry Distro. Skipping",
+                    entry_point.name,
+                )
+                continue
+            logger.debug(
+                "Distribution %s will be configured", entry_point.name
+            )
+            return distro
         except Exception as exc:  # pylint: disable=broad-except
             logger.exception(
                 "Distribution %s configuration failed", entry_point.name
             )
             raise exc
+    return DefaultDistro()
 
 
-def _load_instrumentors():
+def _load_instrumentors(distro):
     package_to_exclude = environ.get(OTEL_PYTHON_DISABLED_INSTRUMENTATIONS, [])
     if isinstance(package_to_exclude, str):
         package_to_exclude = package_to_exclude.split(",")
         # to handle users entering "requests , flask" or "requests, flask" with spaces
         package_to_exclude = [x.strip() for x in package_to_exclude]
 
     for entry_point in iter_entry_points("opentelemetry_instrumentor"):
+        if entry_point.name in package_to_exclude:
+            logger.debug(
+                "Instrumentation skipped for library %s", entry_point.name
+            )
+            continue
+
         try:
-            if entry_point.name in package_to_exclude:
-                logger.debug(
-                    "Instrumentation skipped for library %s", entry_point.name
-                )
-                continue
-            entry_point.load()().instrument()  # type: ignore
+            distro.load_instrumentor(entry_point)
             logger.debug("Instrumented %s", entry_point.name)
         except Exception as exc:  # pylint: disable=broad-except
             logger.exception("Instrumenting of %s failed", entry_point.name)
@@ -80,9 +92,10 @@ def _load_configurators():
 
 def initialize():
     try:
-        _load_distros()
+        distro = _load_distros()
+        distro.configure()
         _load_configurators()
-        _load_instrumentors()
+        _load_instrumentors(distro)
     except Exception:  # pylint: disable=broad-except
         logger.exception("Failed to auto initialize opentelemetry")
     finally:

opentelemetry-instrumentation/src/opentelemetry/instrumentation/distro.py

@@ -20,6 +20,10 @@
 from abc import ABC, abstractmethod
 from logging import getLogger
 
+from pkg_resources import EntryPoint
+
+from opentelemetry.instrumentation.instrumentor import BaseInstrumentor
+
 _LOG = getLogger(__name__)
 
 
@@ -43,5 +47,25 @@ def configure(self, **kwargs):
         """Configure the distribution"""
         self._configure(**kwargs)
 
+    def load_instrumentor(  # pylint: disable=no-self-use
+        self, entry_point: EntryPoint
+    ):
+        """Takes a collection of instrumentation entry points
+        and activates them by instantiating and calling instrument()
+        on each one.
+
+        Distros can override this method to customize the behavior by
+        inspecting each entry point and configuring them in special ways,
+        passing additional arguments, load a replacement/fork instead,
+        skip loading entirely, etc.
+        """
+        instrumentor: BaseInstrumentor = entry_point.load()
+        instrumentor().instrument()
+
+
+class DefaultDistro(BaseDistro):
+    def _configure(self, **kwargs):
+        pass
+
 
-__all__ = ["BaseDistro"]
+__all__ = ["BaseDistro", "DefaultDistro"]

opentelemetry-instrumentation/tests/test_distro.py

@@ -0,0 +1,55 @@
+# Copyright The OpenTelemetry Authors
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+# type: ignore
+
+from unittest import TestCase
+
+from pkg_resources import EntryPoint
+
+from opentelemetry.instrumentation.distro import BaseDistro
+from opentelemetry.instrumentation.instrumentor import BaseInstrumentor
+
+
+class MockInstrumetor(BaseInstrumentor):
+    def _instrument(self, **kwargs):
+        pass
+
+    def _uninstrument(self, **kwargs):
+        pass
+
+
+class MockEntryPoint(EntryPoint):
+    def __init__(self, obj):  # pylint: disable=super-init-not-called
+        self._obj = obj
+
+    def load(self, *args, **kwargs):  # pylint: disable=signature-differs
+        return self._obj
+
+
+class MockDistro(BaseDistro):
+    def _configure(self, **kwargs):
+        pass
+
+
+class TestDistro(TestCase):
+    def test_load_instrumentor(self):
+        # pylint: disable=protected-access
+        distro = MockDistro()
+
+        instrumentor = MockInstrumetor()
+        entry_point = MockEntryPoint(MockInstrumetor)
+
+        self.assertFalse(instrumentor._is_instrumented)
+        distro.load_instrumentor(entry_point)
+        self.assertTrue(instrumentor._is_instrumented)