Tiered caching organises a CDN into a hierarchy: a viewer hits an edge POP, the edge POP asks a regional parent on cache miss, the regional parent asks origin only if it too is missing. Each tier serves as a cache for the tier below it, multiplying the effective hit ratio that origin sees. Cloudflare named this "Tiered Cache" as a product, but the underlying pattern — shield, fan-in cache, parent POP — appears under different names in every major CDN.
Operationally tiered caching is a topology decision. Cloudflare offers "Smart Tiered Caching" that picks the parent POP automatically based on lowest latency to origin; CloudFront's Origin Shield requires the operator to designate a specific region; Akamai's tiered distribution is configured per content provider. Multi-tier setups (edge → parent → super-parent → origin) reduce origin load further for very high-fan-out events but add latency in the cache-miss path.
The key trade-off is freshness vs efficiency. A deeper tier hierarchy means more places to invalidate when a manifest changes (which happens every segment-duration in live streaming). Most CDNs handle this with versioned URLs (each new segment has a unique URL, so invalidation is unnecessary for segments) and short TTLs on manifests (1–2 seconds). Done well, tiered caching gives 95 %+ origin offload even during live events with millions of concurrent viewers.
The book · Volume 3 of 7
Video Streaming: A Complete Guide to Video Delivery: From ABR and CDNs to Players, WebRTC, DRM, and the Economics of Streaming
Tiered caching lets regional parents absorb edge misses, raising the hit ratio origin sees and cutting egress during spikes. This volume covers tiered caching in detail, with CDN cache hierarchies, origin shielding, cache keys, multi-CDN delivery and the economics of origin traffic. Written by Nikolay Sapunov, CEO at Fora Soft.
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