Content Delivery Networks

Move reusable bytes closer to users#

Without an edge layer, a user in India may fetch every video segment from an origin in Virginia. A CDN stores eligible objects at geographically distributed points of presence so a nearby edge can serve repeated requests with less origin traffic and geographic latency.

Cacheability is a policy, not a promise#

The origin is the source location; the edge holds copies. TTL defines freshness, while eviction can remove an object earlier. The cache key decides which requests share a representation. Purge or versioned URLs handle updates. Provider configuration, response headers, object type, authorization, and key policy determine what is actually cached.

Static assets and media segments are common fits. Private downloads can use signed URLs or cookies with carefully designed keys and authorization. Dynamic acceleration may still optimize network paths even when a response is not cached.

Estimate the origin relief#

100K × 1 MB ≈ 100 GB/sec total delivery
100 GB/sec × 5% ≈ 5 GB/sec from origin

Failure and freshness questions#

• Stale objects or slow purge can show old content.
• A missing identity, locale, or encoding dimension in the cache key can serve the wrong representation.
• Cold misses or a hit-rate collapse can overload the origin.
• Personalized content may be unsafe or ineffective to cache.
• Edge delivery reduces origin work but introduces provider cost and another configuration surface.