Add support for OTEL_PROPAGATORS

Fixes #1058

Author: ocelotl

opentelemetry-api/CHANGELOG.md

@@ -2,6 +2,8 @@
 
 ## Unreleased
 
+- Add support for `OTEL_PROPAGATORS`
+  ([#1058](https://github.com/open-telemetry/opentelemetry-python/pull/1058))
 - Store `int`s as `int`s in the global Configuration object
   ([#1118](https://github.com/open-telemetry/opentelemetry-python/pull/1118))
 

opentelemetry-api/setup.cfg

@@ -55,6 +55,9 @@ opentelemetry_meter_provider =
     default_meter_provider = opentelemetry.metrics:DefaultMeterProvider
 opentelemetry_tracer_provider =
     default_tracer_provider = opentelemetry.trace:DefaultTracerProvider
+opentelemetry_propagator =
+    tracecontext = opentelemetry.trace.propagation.tracecontext:TraceContextTextMapPropagator
+    baggage = opentelemetry.baggage.propagation:BaggagePropagator
 
 [options.extras_require]
 test =

opentelemetry-api/src/opentelemetry/propagators/__init__.py

@@ -15,6 +15,18 @@
 """
 API for propagation of context.
 
+The propagators for the
+`opentelemetry.propagators.composite.CompositeHTTPPropagator` can be defined
+via configuration in the `OTEL_PROPAGATORS` environment variable. This variable
+should be set to a comma-separated string of names of values for the
+`opentelemetry_propagator` entry point. For example, setting `OTEL_PROPAGATORS`
+to `tracecontext,baggage` (which is the default value) would instantiate
+`opentelemetry.propagators.composite.CompositeHTTPPropagator` with 2
+propagators, one of type `opentelemetry.trace.propagation.tracecontext.TraceContextTextMapPropagator`
+and other of type `opentelemetry.baggage.propagation.BaggagePropagator`. Notice
+that these propagator classes are defined as `opentelemetry_propagator` entry
+points in the `setup.cfg` file of `opentelemetry`.
+
 Example::
 
     import flask
@@ -54,14 +66,16 @@ def example_route():
 """
 
 import typing
+from logging import getLogger
+
+from pkg_resources import iter_entry_points
 
-from opentelemetry.baggage.propagation import BaggagePropagator
+from opentelemetry.configuration import Configuration
 from opentelemetry.context.context import Context
 from opentelemetry.propagators import composite
 from opentelemetry.trace.propagation import textmap
-from opentelemetry.trace.propagation.tracecontext import (
-    TraceContextTextMapPropagator,
-)
+
+logger = getLogger(__name__)
 
 
 def extract(
@@ -104,9 +118,25 @@ def inject(
     get_global_textmap().inject(set_in_carrier, carrier, context)
 
 
-_HTTP_TEXT_FORMAT = composite.CompositeHTTPPropagator(
-    [TraceContextTextMapPropagator(), BaggagePropagator()],
-)  # type: textmap.TextMapPropagator
+try:
+
+    propagators = []
+
+    for propagator in (
+        Configuration().get("PROPAGATORS", "tracecontext,baggage").split(",")
+    ):
+
+        propagators.append(
+            next(
+                iter_entry_points("opentelemetry_propagator", propagator)
+            ).load()()
+        )
+
+except Exception:  # pylint: disable=broad-except
+    logger.exception("Failed to load configured propagators")
+    raise
+
+_HTTP_TEXT_FORMAT = composite.CompositeHTTPPropagator(propagators)
 
 
 def get_global_textmap() -> textmap.TextMapPropagator:

opentelemetry-api/tests/configuration/test_configuration.py

@@ -20,9 +20,10 @@
 
 
 class TestConfiguration(TestCase):
-    def tearDown(self) -> None:
-        # This call resets the attributes of the Configuration class so that
-        # each test is executed in the same conditions.
+
+    # These calls reset the attributes of the Configuration class so that each
+    # test is executed in the same conditions.
+    def setUp(self) -> None:
         Configuration._reset()
 
     def test_singleton(self) -> None:

opentelemetry-api/tests/propagators/test_propagators.py

@@ -0,0 +1,43 @@
+# 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.
+
+from importlib import reload
+from unittest import TestCase
+from unittest.mock import patch
+
+from opentelemetry.baggage.propagation import BaggagePropagator
+from opentelemetry.trace.propagation.tracecontext import (
+    TraceContextTextMapPropagator,
+)
+
+
+class TestPropagators(TestCase):
+    @patch("opentelemetry.propagators.composite.CompositeHTTPPropagator")
+    def test_default_composite_propagators(self, mock_compositehttppropagator):
+        def test_propagators(propagators):
+
+            propagators = {propagator.__class__ for propagator in propagators}
+
+            self.assertEqual(len(propagators), 2)
+            self.assertEqual(
+                propagators, {TraceContextTextMapPropagator, BaggagePropagator}
+            )
+
+        mock_compositehttppropagator.configure_mock(
+            **{"side_effect": test_propagators}
+        )
+
+        import opentelemetry.propagators
+
+        reload(opentelemetry.propagators)