Analyze web request latency causes

Q: Analyze web request latency causes

This question evaluates a candidate's competency in analyzing and optimizing end-to-end web request latency, covering client-side rendering, network/CDN behavior (HTTP/2 or HTTP/3, TLS, caching), server processing, datastore interactions, and observability for p95 TTFB targets.

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Question

System Design: End-to-End Web Request Latency

Context

You are designing a user-facing web experience that fetches HTML/JSON from an origin and additional static assets from a CDN. Users are global (desktop and mobile). The goal is to reduce end-to-end latency (from user action to usable content), with a target of p95 TTFB < 300 ms for the primary HTML/JSON endpoint and a fast, stable render.

Task

Analyze a single web request end-to-end and do the following:

Break down latency into client-side, network, and server-side components.
Identify likely bottlenecks and how you would measure them.
Propose concrete optimizations for each layer (client, network/CDN, server, data store), including expected impact.
Provide a small numeric example that computes the current latency and demonstrates how your optimizations reduce it.
Outline an instrumentation and rollout plan (validation, guardrails, and success criteria).

Assume HTTP/2 or HTTP/3 is available, TLS is required, and the primary response is cacheable for 60 seconds. Keep your analysis focused and practical for a technical phone screen.

Analyze web request latency causes

System Design: End-to-End Web Request Latency

Context

Task

Solution

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