Improve Flask distributed_tracing documentation

Author: LotharSee

ddtrace/contrib/flask/__init__.py

@@ -10,7 +10,7 @@
 
 and create a `TraceMiddleware` object::
 
-    traced_app = TraceMiddleware(app, tracer, service="my-flask-app")
+    traced_app = TraceMiddleware(app, tracer, service="my-flask-app", distributed_tracing=False)
 
 Here is the end result, in a sample app::
 
@@ -22,12 +22,14 @@
 
     app = Flask(__name__)
 
-    traced_app = TraceMiddleware(app, tracer, service="my-flask-app")
+    traced_app = TraceMiddleware(app, tracer, service="my-flask-app", distributed_tracing=False)
 
     @app.route("/")
     def home():
         return "hello world"
 
+Set `distributed_tracing=True` if this is called remotely from an instrumented application.
+We suggest to enable it only for internal services where headers are under your control.
 """
 
 from ..util import require_modules

ddtrace/contrib/flask/middleware.py

@@ -23,14 +23,14 @@
 
 class TraceMiddleware(object):
 
-    def __init__(self, app, tracer, service="flask", use_signals=True, use_distributed_tracing=False):
+    def __init__(self, app, tracer, service="flask", use_signals=True, distributed_tracing=False):
         self.app = app
         self.app.logger.info("initializing trace middleware")
 
         # save our traces.
         self._tracer = tracer
         self._service = service
-        self._use_distributed_tracing = use_distributed_tracing
+        self._use_distributed_tracing = distributed_tracing
 
         self._tracer.set_service_info(
             service=service,

docs/index.rst

@@ -285,6 +285,7 @@ For that, refer to the configuration of the given integration.
 Supported web frameworks:
 
 - Django
+- Flask
 
 
 HTTP client/server

tests/contrib/flask/test_flask.py

@@ -92,7 +92,7 @@ def handle_my_exception(e):
 # work)
 service = "test.flask.service"
 assert not writer.pop()  # should always be empty
-traced_app = TraceMiddleware(app, tracer, service=service, use_distributed_tracing=True)
+traced_app = TraceMiddleware(app, tracer, service=service, distributed_tracing=True)
 
 # make the app testable
 app.config['TESTING'] = True