Backend Study Lab · Games
← All games

ETag & CDN Revalidation Lab

Follow validators through browser, CDN, and origin while handling 304 responses, representation variants, purge, and bounded staleness.

Concept
Conditional requests and CDN cache operation
Difficulty
Advanced
Play time
8-12 minutes
Path
Data & Performance

Interactive scenario

Playable game area: Make the next backend decision

Use the controls below. Feedback appears immediately and final scores stay in this browser.

Concept notes

Why this decision matters

ETag & CDN Revalidation Lab is focused practice for Conditional requests and CDN cache operation. It explains why each answer is safe, risky, or production-ready.

Trace the complete revalidation chain instead of reasoning about one cache in isolation.

Learning objectives

  • Use validators for selected representations.
  • Operate targeted CDN invalidation.
  • Bound emergency stale response behavior.

How to play

  1. Follow each cache hop.
  2. Choose the validator or invalidation behavior.
  3. Balance correctness, transfer cost, and recovery.

Scoring

  • Correct actions add 250 points.
  • Risky actions reduce simulation indicators.
  • A perfect run scores 1,000.

Backend concept notes

An ETag identifies a selected representation, not an abstract database row.

CDN invalidation must target the real cache key and be verified at the edge.

Common mistakes

  • Sharing one strong ETag across different bytes.
  • Restarting origin to purge a CDN.
  • Serving stale sensitive data.

Review misses from this game

Related Backend Study Lab tools

Use tools from the main site when you want to inspect real inputs.

Keep practicing nearby backend concepts while the mental model is fresh.

Caching Beginner

Cache Eviction Lab

Predict cache hits and misses as requests flow through an LRU cache, then experiment with TTL behavior and stale data tradeoffs.

Time
5-8 minutes
Concept
Cache hits, misses, LRU, TTL, and stale data
  • Data & Performance
  • Algorithmic Reasoning
  • cache
  • LRU
  • TTL
Play Cache Eviction Lab
HTTP Caching Intermediate

HTTP Cache Policy Lab

Choose browser and shared-cache policies for public, personalized, validated, and variant API responses.

Time
7-10 minutes
Concept
HTTP cache policy and sensitive response boundaries
  • Data & Performance
  • http caching
  • cache-control
  • privacy
Play HTTP Cache Policy Lab
Scaling Intermediate

Load Balancer Challenge

Route simulated traffic across backend servers using round robin, weighted round robin, least connections, and random strategies.

Time
6-10 minutes
Concept
Load balancing strategies
  • Production Reliability
  • load balancing
  • scaling
  • latency
Play Load Balancer Challenge

FAQ

Short answers for how this game fits backend interview and study practice.

When is 304 correct?

When the client's validator still matches the selected current representation.

Does 304 include the full response body?

No. The client reuses its stored body.

Leaderboard

Top 10 scores for the current ruleset. No account required.

Loading leaderboard...

    Finish the game to load your latest local score.