Add support for OTEL_PROPAGATORS

Fixes open-telemetry#1058

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

@@ -54,14 +54,16 @@ def example_route():
 """
 
 import typing
+from logging import getLogger
 
-from opentelemetry.baggage.propagation import BaggagePropagator
+from pkg_resources import iter_entry_points
+
+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 +106,25 @@ 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: