fix(telemetry): suppress high-cardinality httpx spans for MCP calls

src/sap_cloud_sdk/core/telemetry/config.py

@@ -43,6 +43,7 @@
 ENV_TRACES_EXPORTER = "OTEL_TRACES_EXPORTER"
 ENV_OTLP_PROTOCOL = "OTEL_EXPORTER_OTLP_PROTOCOL"
 ENV_OTEL_DISABLED = "CLOUD_SDK_OTEL_DISABLED"
+ENV_HIGH_CARDINALITY_URLS = "SAP_CLOUD_SDK_HIGH_CARDINALITY_URLS"
 
 
 def _get_region() -> str:

src/sap_cloud_sdk/core/telemetry/genai_attribute_transformer.py

@@ -53,6 +53,8 @@ def __init__(self, wrapped_exporter: SpanExporter):
             "GenAI attribute transformer initialized (minimal normalization enabled)"
         )
 
+    _SUPPRESS_ATTR = "sap.cloud_sdk.suppress"
+
     def export(self, spans: Sequence[ReadableSpan]) -> SpanExportResult:
         """
         Export spans after transforming attributes.
@@ -65,6 +67,8 @@ def export(self, spans: Sequence[ReadableSpan]) -> SpanExportResult:
         """
         transformed = []
         for span in spans:
+            if span.attributes and span.attributes.get(self._SUPPRESS_ATTR):
+                continue
             try:
                 transformed.append(self._normalize_attributes(span))
             except Exception as e:

src/sap_cloud_sdk/core/telemetry/instrumentation/instrumentors/httpx.py

@@ -1,21 +1,63 @@
+import os
+import re
+
 from opentelemetry.instrumentation.httpx import HTTPXClientInstrumentor
+from opentelemetry.trace import Span
 
 from sap_cloud_sdk.core.telemetry.instrumentation.base import LibraryInstrumentor
 from sap_cloud_sdk.core.telemetry.instrumentation._registry import register
+from sap_cloud_sdk.core.telemetry.config import ENV_HIGH_CARDINALITY_URLS
+
+# Internal attribute that marks a span for suppression at export time.
+# The span is still created so that W3C traceparent headers are injected
+# into the outgoing request, preserving distributed trace context.
+_SUPPRESS_ATTR = "sap.cloud_sdk.suppress"
+
+
+def _compile_patterns() -> list[re.Pattern]:
+    raw = os.getenv(ENV_HIGH_CARDINALITY_URLS, "")
+    patterns = [p.strip() for p in raw.split(",") if p.strip()]
+    return [re.compile(re.escape(p)) for p in patterns]
+
+
+_patterns: list[re.Pattern] = _compile_patterns()
+
+
+def _is_high_cardinality(url: str) -> bool:
+    return any(p.search(url) for p in _patterns)
+
+
+def _request_hook(span: Span, request) -> None:
+    if _is_high_cardinality(str(request.url)):
+        span.set_attribute(_SUPPRESS_ATTR, True)
+
+
+async def _async_request_hook(span: Span, request) -> None:
+    if _is_high_cardinality(str(request.url)):
+        span.set_attribute(_SUPPRESS_ATTR, True)
+
 
 _instrumentor = HTTPXClientInstrumentor()
 
 
 class HttpxInstrumentor(LibraryInstrumentor):
-    """Instruments httpx sync and async clients with OTel spans and W3C header propagation."""
+    """Instruments httpx sync and async clients with OTel spans and W3C header propagation.
+
+    Spans for URLs matching SAP_CLOUD_SDK_HIGH_CARDINALITY_URLS (comma-separated substrings,
+    unset by default) are marked for suppression at export time. The span is still created so
+    that W3C traceparent headers propagate to the downstream service.
+    """
 
     library_name = "httpx"
 
     def is_instrumented(self) -> bool:
         return _instrumentor.is_instrumented_by_opentelemetry
 
     def _instrument(self, **kwargs) -> None:
-        _instrumentor.instrument()
+        _instrumentor.instrument(
+            request_hook=_request_hook,
+            async_request_hook=_async_request_hook,
+        )
 
     def _uninstrument(self) -> None:
         _instrumentor.uninstrument()