[Lambda] Create dummy segment when trace header is incomplete

This change makes it so that when the trace header is incomplete no new subsegments will be added. Customers can call the X-Ray SDK APIs without any output in this case.

Author: majanjua-amzn

aws_xray_sdk/core/lambda_launcher.py

@@ -3,6 +3,7 @@
 import threading
 
 from aws_xray_sdk import global_sdk_config
+from .models.dummy_entities import DummySegment
 from .models.facade_segment import FacadeSegment
 from .models.trace_header import TraceHeader
 from .context import Context
@@ -44,7 +45,7 @@ class LambdaContext(Context):
     """
     Lambda service will generate a segment for each function invocation which
     cannot be mutated. The context doesn't keep any manually created segment
-    but instead every time ``get_trace_entity()`` gets called it refresh the facade
+    but instead every time ``get_trace_entity()`` gets called it refresh the
     segment based on environment variables set by Lambda worker.
     """
     def __init__(self):
@@ -65,12 +66,12 @@ def end_segment(self, end_time=None):
 
     def put_subsegment(self, subsegment):
         """
-        Refresh the facade segment every time this function is invoked to prevent
+        Refresh the segment every time this function is invoked to prevent
         a new subsegment from being attached to a leaked segment/subsegment.
         """
         current_entity = self.get_trace_entity()
 
-        if not self._is_subsegment(current_entity) and current_entity.initializing:
+        if not self._is_subsegment(current_entity) and (getattr(current_entity, 'initializing', None) or isinstance(current_entity, DummySegment)):
             if global_sdk_config.sdk_enabled():
                 log.warning("Subsegment %s discarded due to Lambda worker still initializing" % subsegment.name)
             return
@@ -99,9 +100,9 @@ def get_trace_entity(self):
 
     def _refresh_context(self):
         """
-        Get current facade segment. To prevent resource leaking in Lambda worker,
+        Get current segment. To prevent resource leaking in Lambda worker,
         every time there is segment present, we compare its trace id to current
-        environment variables. If it is different we create a new facade segment
+        environment variables. If it is different we create a new segment
         and clean up subsegments stored.
         """
         header_str = os.getenv(LAMBDA_TRACE_HEADER_KEY)
@@ -136,8 +137,8 @@ def handle_context_missing(self):
 
     def _initialize_context(self, trace_header):
         """
-        Create a facade segment based on environment variables
-        set by AWS Lambda and initialize storage for subsegments.
+        Create a segment based on environment variables set by
+        AWS Lambda and initialize storage for subsegments.
         """
         sampled = None
         if not global_sdk_config.sdk_enabled():
@@ -148,12 +149,17 @@ def _initialize_context(self, trace_header):
         elif trace_header.sampled == 1:
             sampled = True
 
-        segment = FacadeSegment(
-            name='facade',
-            traceid=trace_header.root,
-            entityid=trace_header.parent,
-            sampled=sampled,
-        )
+        segment = None
+        if not trace_header.root or not trace_header.parent or trace_header.sampled is None:
+            segment = DummySegment()
+            log.debug("Creating NoOp/Dummy parent segment")
+        else:
+            segment = FacadeSegment(
+                name='facade',
+                traceid=trace_header.root,
+                entityid=trace_header.parent,
+                sampled=sampled,
+            )
         segment.save_origin_trace_header(trace_header)
         setattr(self._local, 'segment', segment)
         setattr(self._local, 'entities', [])

tests/test_lambda_context.py

@@ -67,18 +67,19 @@ def test_disable():
 
 
 def test_non_initialized():
-    # Context that hasn't been initialized by lambda container should not add subsegments to the facade segment.
+    # Context that hasn't been initialized by lambda container should not add subsegments to the dummy segment.
     temp_header_var = os.environ[lambda_launcher.LAMBDA_TRACE_HEADER_KEY]
     del os.environ[lambda_launcher.LAMBDA_TRACE_HEADER_KEY]
 
     temp_context = lambda_launcher.LambdaContext()
-    facade_segment = temp_context.get_trace_entity()
-    subsegment = Subsegment("TestSubsegment", "local", facade_segment)
+    dummy_segment = temp_context.get_trace_entity()
+    subsegment = Subsegment("TestSubsegment", "local", dummy_segment)
     temp_context.put_subsegment(subsegment)
 
-    assert temp_context.get_trace_entity() == facade_segment
+    assert temp_context.get_trace_entity() == dummy_segment
 
     # "Lambda" container added metadata now. Should see subsegment now.
+    # The following put_segment call will overwrite the dummy segment in the context with an intialized facade segment that accepts a subsegment.
     os.environ[lambda_launcher.LAMBDA_TRACE_HEADER_KEY] = temp_header_var
     temp_context.put_subsegment(subsegment)