Update Step Functions Parent ID Generation (#559)

Co-authored-by: purple4reina <rey.abolofia@datadoghq.com>

Author: avedmala

datadog_lambda/tracing.py

@@ -385,21 +385,24 @@ def _parse_high_64_bits(trace_tags: str) -> str:
 
 def _generate_sfn_parent_id(context: dict) -> int:
     """
-    The upstream Step Function can propagate its execution context to downstream Lambdas. The
-    Lambda can use these details to share the same traceID and infer its parent's spanID.
+    Generates a stable parent span ID for a downstream Lambda invoked by a Step Function. The
+    upstream Step Function execution context is used to infer the parent's span ID, ensuring trace
+    continuity.
 
-    Excluding redriveCount when its 0 to account for cases where customers are using an old
-    version of the Lambda layer that doesn't use this value for its parentID generation.
+    `RetryCount` and `RedriveCount` are appended only when both are nonzero to maintain
+    compatibility with older Lambda layers that did not include these fields.
     """
     execution_id = context.get("Execution").get("Id")
     redrive_count = context.get("Execution").get("RedriveCount", 0)
     state_name = context.get("State").get("Name")
     state_entered_time = context.get("State").get("EnteredTime")
+    retry_count = context.get("State").get("RetryCount", 0)
 
-    redrive_postfix = "" if redrive_count == 0 else f"#{redrive_count}"
+    include_counts = not (retry_count == 0 and redrive_count == 0)
+    counts_suffix = f"#{retry_count}#{redrive_count}" if include_counts else ""
 
     return _deterministic_sha256_hash(
-        f"{execution_id}#{state_name}#{state_entered_time}{redrive_postfix}",
+        f"{execution_id}#{state_name}#{state_entered_time}{counts_suffix}",
         HIGHER_64_BITS,
     )
 

tests/test_tracing.py

@@ -622,6 +622,7 @@ def test_step_function_trace_data(self):
                 "Name": "72a7ca3e-901c-41bb-b5a3-5f279b92a316",
                 "RoleArn": "arn:aws:iam::425362996713:role/service-role/StepFunctions-abhinav-activity-state-machine-role-22jpbgl6j",
                 "StartTime": "2024-12-04T19:38:04.069Z",
+                "RedriveCount": 0,
             },
             "State": {
                 "Name": "Lambda Invoke",
@@ -657,6 +658,51 @@ def test_step_function_trace_data(self):
             expected_context,
         )
 
+        @with_trace_propagation_style("datadog")
+        def test_step_function_trace_data_retry(self):
+            lambda_ctx = get_mock_context()
+            sfn_event = {
+                "Execution": {
+                    "Id": "arn:aws:states:sa-east-1:425362996713:execution:abhinav-activity-state-machine:72a7ca3e-901c-41bb-b5a3-5f279b92a316",
+                    "Name": "72a7ca3e-901c-41bb-b5a3-5f279b92a316",
+                    "RoleArn": "arn:aws:iam::425362996713:role/service-role/StepFunctions-abhinav-activity-state-machine-role-22jpbgl6j",
+                    "StartTime": "2024-12-04T19:38:04.069Z",
+                    "RedriveCount": 0,
+                },
+                "State": {
+                    "Name": "Lambda Invoke",
+                    "EnteredTime": "2024-12-04T19:38:04.118Z",
+                    "RetryCount": 1,
+                },
+                "StateMachine": {
+                    "Id": "arn:aws:states:sa-east-1:425362996713:stateMachine:abhinav-activity-state-machine",
+                    "Name": "abhinav-activity-state-machine",
+                },
+            }
+            ctx, source, event_source = extract_dd_trace_context(sfn_event, lambda_ctx)
+            self.assertEqual(source, "event")
+            expected_context = Context(
+                trace_id=435175499815315247,
+                span_id=5063839446130725204,
+                sampling_priority=1,
+                meta={"_dd.p.tid": "3e7a89d1b7310603"},
+            )
+            self.assertEqual(ctx, expected_context)
+            self.assertEqual(
+                get_dd_trace_context(),
+                {
+                    TraceHeader.TRACE_ID: "435175499815315247",
+                    TraceHeader.PARENT_ID: "10713633173203262661",
+                    TraceHeader.SAMPLING_PRIORITY: "1",
+                    TraceHeader.TAGS: "_dd.p.tid=3e7a89d1b7310603",
+                },
+            )
+            create_dd_dummy_metadata_subsegment(ctx, XraySubsegment.TRACE_KEY)
+            self.mock_send_segment.assert_called_with(
+                XraySubsegment.TRACE_KEY,
+                expected_context,
+            )
+
     # https://github.com/DataDog/logs-backend/blob/c17618cb552fc369ca40282bae0a65803f82f694/domains/serverless/apps/logs-to-traces-reducer/src/test/resources/test-json-files/stepfunctions/RedriveTest/snapshots/RedriveLambdaSuccessTraceMerging.json#L46
     @with_trace_propagation_style("datadog")
     def test_step_function_trace_data_redrive(self):
@@ -683,7 +729,7 @@ def test_step_function_trace_data_redrive(self):
         self.assertEqual(source, "event")
         expected_context = Context(
             trace_id=435175499815315247,
-            span_id=5063839446130725204,
+            span_id=8782364156266188026,
             sampling_priority=1,
             meta={"_dd.p.tid": "3e7a89d1b7310603"},
         )
@@ -716,6 +762,7 @@ def test_step_function_trace_data_lambda_root(self):
                 "State": {
                     "Name": "my-awesome-state",
                     "EnteredTime": "Mon Nov 13 12:43:33 PST 2023",
+                    "RetryCount": 0,
                 },
                 "x-datadog-trace-id": "5821803790426892636",
                 "x-datadog-tags": "_dd.p.dm=-0,_dd.p.tid=672a7cb100000000",
@@ -759,6 +806,7 @@ def test_step_function_trace_data_sfn_root(self):
                 "State": {
                     "Name": "my-awesome-state",
                     "EnteredTime": "Mon Nov 13 12:43:33 PST 2023",
+                    "RetryCount": 0,
                 },
                 "RootExecutionId": "4875aba4-ae31-4a4c-bf8a-63e9eee31dad",
                 "serverless-version": "v1",