Add warning when no opentelemetry_configurator entry points found

CHANGELOG.md

@@ -13,6 +13,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added
 
+- `opentelemetry-instrumentation`: Add warning when no `opentelemetry_configurator` 
+  entry points are found, suggesting to install `opentelemetry-distro`.
+  ([#4543](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/4543))
 - Bump `pylint` to `4.0.5`
   ([#4244](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/4244))
 - `opentelemetry-instrumentation-sqlite3`: Add uninstrument, error status, suppress, and no-op tests

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

@@ -187,3 +187,10 @@ def _load_configurators():
         except Exception as exc:  # pylint: disable=broad-except
             _logger.exception("Configuration of %s failed", entry_point.name)
             raise exc
+
+    if configured is None:
+        _logger.warning(
+            "No configurator found. Make sure 'opentelemetry-distro' is "
+            "installed if you are using automatic instrumentation. "
+            "See https://opentelemetry.io/docs/zero-code/python/ for details."
+        )

opentelemetry-instrumentation/tests/auto_instrumentation/test_load.py

@@ -67,6 +67,14 @@ def test_load_configurators(self, iter_mock):  # pylint: disable=no-self-use
     )
     def test_load_configurators_no_ep(self, iter_mock):  # pylint: disable=no-self-use
         iter_mock.return_value = ()
+        with self.assertLogs(
+            "opentelemetry.instrumentation.auto_instrumentation._load",
+            level="WARNING",
+        ) as cm:
+            _load._load_configurators()
+        self.assertTrue(
+            any("opentelemetry-distro" in msg for msg in cm.output)
+        )
         # Confirm method does not crash if not entry points exist.
         _load._load_configurators()