This question is basically six questions duct-taped together and I did not pace myself well.
Start by decomposing the request path into distinct segments and defining how you'd measure each (client-side RUM, server-side tracing, synthetic tests). Then walk through instrumentation, attribution, tail latency analysis, and layered optimizations, anchoring everything with a concrete numeric example that shows baseline vs. improved latency and how you'd set SLIs/SLOs.
Pro tip: Emphasize that you'd instrument first and optimize second—many engineers jump to fixes without data. Also, explicitly call out that tail latency (p95/p99) often dominates user experience and requires different techniques (hedged requests, timeouts, circuit breakers) than median latency.
Break the end-to-end path into segments (browser, CDN, LB, each microservice, cache, DB, third-party) and define a latency budget per segment. Use a waterfall model to visualize where time is spent.
Implement Real User Monitoring (RUM) with Navigation Timing API and Resource Timing API on the client, and distributed tracing (e.g., OpenTelemetry) with span propagation on the server. Ensure trace context flows through all services.
Correlate client-side timings with server-side traces to attribute delays to frontend vs backend. Analyze p50, p95, p99 latencies; identify outliers via trace sampling and log analysis, looking for GC pauses, network retries, cache misses, or slow third-party calls.
Suggest optimizations at each layer: browser (caching, code splitting), CDN (edge caching, Brotli), LB (connection pooling, keep-alive), microservices (async I/O, batching), caches (Redis, TTL tuning), DB (indexing, read replicas), third-party (timeouts, circuit breakers).
Define SLIs like p95 latency for key endpoints, error rate, and throughput. Set SLOs (e.g., p95 < 200ms). Provide a numeric example: baseline p95 = 800ms, after optimizations p95 = 300ms, with breakdown of savings per layer.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.