Merge pull request #145 from evaline-ju/weather-trace-langchain

feat: Trace weather agent to MCP gateway tool calls

Author: evaline-ju

a2a/weather_service/pyproject.toml

@@ -19,6 +19,8 @@ dependencies = [
     "langchain-mcp-adapters>=0.1.0",
     "python-keycloak>=5.5.1",
     "opentelemetry-exporter-otlp",
+    # Auto-instrument httpx so outgoing MCP tool calls propagate traceparent
+    "opentelemetry-instrumentation-httpx>=0.49b0",
     # OpenTelemetry GenAI semantic convention instrumentation
     # Emits spans with gen_ai.* attributes for MLflow compatibility
     "opentelemetry-instrumentation-openai>=0.34b0",

a2a/weather_service/src/weather_service/graph.py

@@ -17,7 +17,12 @@ class ExtendedMessagesState(MessagesState):
 
 
 def get_mcpclient(headers=None):
-    """Create MCP client, optionally forwarding headers (e.g. Authorization)."""
+    """Create MCP client, optionally forwarding headers (e.g. Authorization).
+
+    Trace context propagation (traceparent headers) to the MCP gateway is
+    handled automatically by opentelemetry-instrumentation-httpx, which
+    injects the current span's context on every outgoing HTTP request.
+    """
     mcp_config = {
         "url": os.getenv("MCP_URL", "http://localhost:8000/mcp"),
         "transport": os.getenv("MCP_TRANSPORT", "streamable_http"),

a2a/weather_service/src/weather_service/observability.py

@@ -134,6 +134,19 @@ def setup_observability() -> None:
         )
     )
 
+    # Instrument httpx for automatic traceparent propagation on outgoing requests.
+    # langchain-mcp-adapters uses httpx for streamable_http transport, so each MCP
+    # tool call will automatically carry the current span's traceparent header
+    try:
+        from opentelemetry.instrumentation.httpx import HTTPXClientInstrumentor
+
+        HTTPXClientInstrumentor().instrument()
+        logger.info("httpx instrumented for automatic trace context propagation")
+    except ImportError:
+        logger.warning(
+            "opentelemetry-instrumentation-httpx not available - MCP tool calls will not propagate trace context"
+        )
+
     # Instrument OpenAI for GenAI semantic conventions
     try:
         from opentelemetry.instrumentation.openai import OpenAIInstrumentor
@@ -406,7 +419,7 @@ def create_tracing_middleware():
 
     async def tracing_middleware(request: Request, call_next):
         # Skip non-API paths (health checks, agent card, etc.)
-        if request.url.path in ["/health", "/ready", "/.well-known/agent-card.json"]:
+        if request.url.path in ["/health", "/ready", "/.well-known/agent-card.json", "/.well-known/agent.json"]:
             return await call_next(request)
 
         tracer = get_tracer()
@@ -431,10 +444,12 @@ async def tracing_middleware(request: Request, call_next):
         except Exception as e:
             logger.debug(f"Could not parse request body: {e}")
 
-        # Break parent chain to make this a true root span
-        # Without this, the span would inherit parent from W3C Trace Context headers
-        empty_ctx = context.Context()
-        detach_token = context.attach(empty_ctx)
+        # Extract incoming W3C Trace Context from request headers to connect
+        # agent spans to MCP gateway spans. Callers without traceparent still
+        # get root spans (extract returns empty context), while callers with traceparent
+        # (like MCP gateway) get connected end-to-end traces
+        incoming_ctx = extract(dict(request.headers))
+        detach_token = context.attach(incoming_ctx)
 
         try:
             # Create root span with correct GenAI naming convention