Carry trace context across the Redis Stream by hand

Redis Streams have no headers, so the gateway injects traceparent into
the message fields inside a PRODUCER span. The notifier and audit
consumers extract it and open one CONSUMER span per message, so their
DB and XACK spans join the transaction's trace. The idle XREADGROUP poll
runs under suppress_instrumentation (it was a ~2s root trace every loop),
and audit strips the trace fields so its stored payload is unchanged.

The gateway also stops tracing its frontend's /api/health/ polling.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

services/audit/consumer.py

@@ -3,12 +3,16 @@ import json
 import logging
 
 import sqlalchemy as sa
+from opentelemetry import propagate, trace
+from opentelemetry.instrumentation.utils import suppress_instrumentation
+from opentelemetry.trace import SpanKind
 
 from common.db import Session
 from common.redis_client import redis_client
 from common.settings import settings
 
 logger = logging.getLogger("audit")
+tracer = trace.get_tracer(__name__)
 
 GROUP = "audit"
 CONSUMER = "audit-1"
@@ -23,13 +27,16 @@ async def ensure_group():
 
 
 async def _handle(fields: dict):
+    # Store the business fields only, not the propagated trace context.
+    trace_fields = propagate.get_global_textmap().fields
+    payload = {k: v for k, v in fields.items() if k not in trace_fields}
     async with Session() as session:
         await session.execute(
             sa.text(
                 "INSERT INTO audit_events (transaction_id, event_type, payload, recorded_at) "
                 "VALUES (:tx_id, 'transaction_processed', CAST(:payload AS jsonb), now())"
             ),
-            {"tx_id": fields.get("transaction_id"), "payload": json.dumps(fields)},
+            {"tx_id": fields.get("transaction_id"), "payload": json.dumps(payload)},
         )
         await session.commit()
 
@@ -42,6 +49,8 @@ async def run():
     logger.info("audit consumer started")
     while True:
         try:
+            # The blocking poll would otherwise be a ~2s root trace every loop.
+            with suppress_instrumentation():
                 resp = await redis_client.xreadgroup(
                     groupname=GROUP,
                     consumername=CONSUMER,
@@ -61,6 +70,19 @@ async def run():
 
         for _, messages in resp:
             for msg_id, fields in messages:
+                # Parent is the gateway's PRODUCER span, carried in the message.
+                with tracer.start_as_current_span(
+                    f"process {settings.stream_name}",
+                    context=propagate.extract(fields),
+                    kind=SpanKind.CONSUMER,
+                    attributes={
+                        "messaging.system": "redis",
+                        "messaging.destination.name": settings.stream_name,
+                        "messaging.operation.type": "process",
+                        "messaging.consumer.group.name": GROUP,
+                        "messaging.message.id": msg_id,
+                    },
+                ):
                     try:
                         await _handle(fields)
                     except Exception:

services/gateway/app.py

@@ -24,7 +24,7 @@ app = FastAPI(title=SERVICE_NAME)
 
 FastAPIInstrumentor.instrument_app(
     app,
-    excluded_urls="/healthz",
+    excluded_urls="/healthz,/api/health/",
     exclude_spans=["receive", "send"],
 )
 

services/gateway/orchestrator.py

@@ -3,6 +3,8 @@ import time
 import uuid
 
 import httpx
+from opentelemetry import propagate, trace
+from opentelemetry.trace import SpanKind
 
 from common.http import downstream_client
 from common.redis_client import redis_client
@@ -11,6 +13,7 @@ from common.settings import settings
 from . import chaos
 
 logger = logging.getLogger("gateway")
+tracer = trace.get_tracer(__name__)
 
 REJECT_THRESHOLD = 0.8
 
@@ -129,17 +132,29 @@ async def create_transaction(payload: dict, request_id: str) -> dict:
         settled = settle_resp.json()
 
         try:
-            await redis_client.xadd(
-                settings.stream_name,
-                {
+            fields = {
                 "transaction_id": tx_id,
                 "account_id": created["account_id"],
                 "kind": created["kind"],
                 "amount_minor": str(created["amount_minor"]),
                 "status": settled["status"],
                 "risk_score": str(risk_score),
+            }
+            with tracer.start_as_current_span(
+                f"send {settings.stream_name}",
+                kind=SpanKind.PRODUCER,
+                attributes={
+                    "messaging.system": "redis",
+                    "messaging.destination.name": settings.stream_name,
+                    "messaging.operation.type": "send",
                 },
-            )
+            ) as span:
+                # Redis Streams carry no trace context, so it travels in the
+                # message itself. Injected inside the PRODUCER span, so the
+                # consumers' parent is this span.
+                propagate.inject(fields)
+                msg_id = await redis_client.xadd(settings.stream_name, fields)
+                span.set_attribute("messaging.message.id", msg_id)
         except Exception:
             logger.exception(f"failed to publish transaction {tx_id} to the stream")
 

services/notifier/consumer.py

@@ -4,6 +4,9 @@ import random
 import uuid
 
 import sqlalchemy as sa
+from opentelemetry import propagate, trace
+from opentelemetry.instrumentation.utils import suppress_instrumentation
+from opentelemetry.trace import SpanKind
 
 from common.db import Session
 from common.redis_client import redis_client
@@ -12,6 +15,7 @@ from common.settings import settings
 from . import chaos
 
 logger = logging.getLogger("notifier")
+tracer = trace.get_tracer(__name__)
 
 GROUP = "notifier"
 CONSUMER = "notifier-1"
@@ -52,6 +56,8 @@ async def run():
     logger.info("notifier consumer started")
     while True:
         try:
+            # The blocking poll would otherwise be a ~2s root trace every loop.
+            with suppress_instrumentation():
                 resp = await redis_client.xreadgroup(
                     groupname=GROUP,
                     consumername=CONSUMER,
@@ -71,6 +77,19 @@ async def run():
 
         for _, messages in resp:
             for msg_id, fields in messages:
+                # Parent is the gateway's PRODUCER span, carried in the message.
+                with tracer.start_as_current_span(
+                    f"process {settings.stream_name}",
+                    context=propagate.extract(fields),
+                    kind=SpanKind.CONSUMER,
+                    attributes={
+                        "messaging.system": "redis",
+                        "messaging.destination.name": settings.stream_name,
+                        "messaging.operation.type": "process",
+                        "messaging.consumer.group.name": GROUP,
+                        "messaging.message.id": msg_id,
+                    },
+                ):
                     try:
                         await _handle(fields)
                     except Exception: