Design a system for managing a content delivery network (CDN).

Question

Anonymous · Accepted Answer

Functional Requirements

1. Upload content (images, videos, static files) → get a globally served URL

2. Serve from nearest edge server, not origin

3. Cache miss → pull from origin, cache locally, serve

4. Purge/invalidate cached content on demand

5. Analytics -- hit/miss ratios, bandwidth, latency per region

6. Custom domains with TLS

Non-Functional Requirements

- Sub-50ms on cache hits -- that's the whole point of a CDN

- 99.99% uptime, edge goes down → DNS reroutes automatically

- Millions of req/sec, petabyte-scale storage, heavily read-biased

- Eventual consistency on cache propagation (5-10s purge delay is fine)

- DDoS protection at edge, TLS everywhere, signed URLs for private content

Core Entities

- Asset : file being served (ID, origin URL, content type, size, hash, TTL,
owner)

- EdgeNode : server at a geographic location (region, IP, health, load,
capacity)

- CacheEntry : asset to edge mapping (cached when, expires when, hit count,
evicted via LRU)

- Distribution : customer's CDN config (custom domain, origin server, TLS cert,
caching rules)

- PurgeRequest :invalidation job (URL pattern, status, edge confirmations)