Diagnose Serial N+1 API Calls With Tempo + proxymock

A hands-on Go catalog API lab demonstrates how to diagnose and safely fix serial downstream inventory calls using Grafana Tempo tracing and proxymock traffic recording and replay. An inbound request containing eight product IDs produces eight sequential inventory lookups, creating a roughly 302 ms critical path despite low CPU use and no failures; Tempo identifies the non-overlapping span pattern, while proxymock connects it to the recorded request input and preserves dependency responses for repeatable testing. The workflow records traffic, runs correctness and load replays with saved timestamp windows, uses MCP tools to inspect recorded exchanges and Tempo traces, and requires evidence of response equivalence before code changes. The proposed fix uses bounded concurrency of four calls while preserving validation, request order, cancellation, errors, and response values, then validates the candidate against the same recording through stable-field response diffs, functional replays, load results, and updated traces. Reference results retained eight dependency calls and 17 spans but changed the trace from eight serial calls to two waves of four, reducing critical-path latency from about 302 ms to 85 ms and increasing local load throughput, while noting that these controlled offline measurements do not establish production capacity or replace separate evaluation of batching alternatives.

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