Web Fundamentals

DNS Resolution: Path, TTL, Caching & Frontend Impact

Web Fundamentals Map

Rendering & Browser Architecture

Critical Rendering Path Script Loading Patterns (async/defer)Event Loop Deep Dive JavaScript Module Systems (CJS, ESM, UMD)Dynamic Module Loading (import())Import on Interaction Import on Visibility Browser Rendering Pipeline & Layout Thrashing Rendering Strategies (CSR, SSR, SSG, ISR)Streaming SSR & Progressive HTML Islands Architecture React Server Components Framework Reactivity (React, Vue, Svelte, Solid)HTTP/1.1 vs HTTP/2 vs HTTP/3 (QUIC)DNS Resolution & TTL Caching

Performance

Core Web Vitals: LCP, INP, CLS Performance Optimization Trade-offs Critical Resource Prioritization Code Splitting & Dynamic Imports Tree Shaking & Dead Code Elimination Lazy Loading Resource Hints: Preload, Prefetch & Preconnect Text Compression: Gzip & Brotli Image & Video Optimization Adaptive Loading List Virtualization Web Workers vs Main Thread Memory Leaks: Detection & Prevention Managing Third-Party Scripts How CDNs Work HTTP Caching Deep Dive Service Workers & Offline Strategy PWA Fundamentals

Security

Cross-Site Scripting (XSS)Cross-Site Request Forgery (CSRF)CORS Explained CORS Preflight, Credentials & Misconfigurations Content Security Policy (CSP)Why is HTTPS Secure? (TLS/SSL)Authorization Best Practices Cookie Security & Session Hardening

State & Data Architecture

State Management Guide (Context vs Zustand vs Redux)React Query & Server State Caching Data Fetching Patterns Caching Strategies Pagination: Offset vs Cursor-Based Real-time Communication (WebSocket, SSE, Polling)

mediumWeb Fundamentals

DNS Resolution: Path, TTL, Caching & Frontend Impact

Learn the interview-ready mental model, practical trade-offs, and production patterns for this web fundamentals topic.

Topic content

TL;DRDNS = distributed cache hierarchy. TTL controls agility vs cache hit rate. Changes propagate gradually.

High Signal

Google

Meta

Netflix

Agoda

30-Second Answerstart every interview with this

DNS is a layered, distributed caching system. A lookup traverses client → OS → recursive resolver → authoritative nameserver. TTL determines how long responses are cached. Understanding resolution path, caching behavior, and TTL trade-offs is essential for frontend performance, migrations, and incident recovery.

Your browser asks the local post office (OS cache). If not known, it asks the regional hub (recursive resolver). The hub walks up the hierarchy (root → TLD → authoritative) and brings back the address. Once delivered, everyone along the route keeps a copy for the TTL duration. Changing an address doesn't instantly update every post office — old copies must expire.

Browser / OS Cache

Recursive Resolver

Root → TLD → Authoritative

Response + TTL Caching at Every Layer

1DNS Resolution Path

Client → OS cache → Recursive resolver → Root → TLD → Authoritative nameserver. Most lookups are served from cache after the first resolution.

resolution-flowtext

Browser → OS → Recursive Resolver → Root → TLD → Authoritative

2Key Record Types

A/AAAA for IP addresses, CNAME for aliases (common with CDNs), TXT for verification. CNAME chains add extra lookups.

3TTL Strategy

Short TTL (30-300s) = fast failover/migrations. Long TTL (1h–24h) = better cache hit rate and lower load. Lower TTL before big changes.

4Caching Layers & Negative Caching

Browser, OS, Recursive Resolver, ISP/CDN layers. Negative caching (NXDOMAIN) can delay new record visibility.

Key Takeaways

✓DNS is a multi-layer distributed cache, not a real-time lookup
✓TTL balances propagation speed vs cache efficiency
✓Lower TTL hours before migrations or failovers
✓Negative caching can delay visibility of new records
✓DNS impacts cold-start TTFB and CDN performance
✓Always validate changes with real-user metrics and multiple resolvers

Topic Guide

On this page