78c8e6fb99
**Implements**: [SEP-2448: server execution telemetry] (https://github.com/modelcontextprotocol/modelcontextprotocol/pull/2448) **Description:** **The Observability Gap (The Problem)** MCP clients propagate trace context to servers, but server-side execution remains a black box. The client sees a single tools/call or resources/read span; everything the server does (auth checks, policy evaluation, API calls, sub-tool invocations) is invisible. In cross-organization deployments, clients and servers use separate observability backends with no shared collector access, making traditional span export useless. <img width="1015" height="450" alt="Screenshot 2026-03-23 at 3 43 21 PM" src="https://github.com/user-attachments/assets/58c817b5-fee6-46a3-9877-d523a25368ad" /> **Server Execution Telemetry (The Solution)** Servers advertise serverExecutionTelemetry and return a curated slice of their execution spans directly in _meta.otel of the response. Clients ingest these verbatim OTLP spans into their own collector, stitching server-side execution into their distributed trace; no shared infrastructure required. The black box becomes transparent. <img width="945" height="574" alt="Screenshot 2026-03-23 at 3 43 44 PM" src="https://github.com/user-attachments/assets/38d97c94-aa73-4e62-9b4e-3264600e5ed0" /> . **Summary:** Implement MCP serverExecutionTelemetry capability that enables cross-organization distributed tracing by returning server-side OpenTelemetry spans to clients inline via _meta.otel.traces. Server-side (middleware): - TelemetryPassbackMiddleware intercepts tools/call and resources/read - ContextVarSpanCollector isolates span collection per-request via ContextVar - Propagates traceparent from client request for distributed trace stitching - Serializes collected spans to verbatim OTLP JSON (resourceSpans format), directly POSTable to /v1/traces - Top-level span filtering by default; full span tree via detailed opt-in - Middleware advertises capabilities via get_capabilities() on the Middleware base class - Provisional API: FutureWarning emitted until SEP-2448 is ratified Client-side (reference agent): - LangChain ReAct agent connects to MCP server via streamable_http_client with OAuth 2.1 - Detects serverExecutionTelemetry capability at initialization - Dynamically wraps discovered MCP tools with traceparent propagation and _meta.otel span request - Ingests returned server spans into Jaeger (OTLP JSON) and Galileo (OTLP protobuf) - Two-act demo: --no-passback (black box) vs default (full server-side visibility) Dependencies: - opentelemetry-api and opentelemetry-sdk added to arcade-mcp-server Bump arcade-mcp-server version to 1.18.0.
19 lines
523 B
Python
19 lines
523 B
Python
"""MCP Middleware System"""
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from arcade_mcp_server.middleware.base import (
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CallNext,
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Middleware,
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MiddlewareContext,
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)
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from arcade_mcp_server.middleware.error_handling import ErrorHandlingMiddleware
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from arcade_mcp_server.middleware.logging import LoggingMiddleware
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from arcade_mcp_server.middleware.telemetry import TelemetryPassbackMiddleware
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__all__ = [
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"CallNext",
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"ErrorHandlingMiddleware",
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"LoggingMiddleware",
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"Middleware",
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"MiddlewareContext",
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"TelemetryPassbackMiddleware",
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]
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