Single-tier CDN cache eats bandwidth. Multi-tier hierarchy — edge → regional → origin — reduces origin load by 90%+.

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Three-tier: edges → regional → origin shield → origin
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Edge tier

Physically close to users. 100s of PoPs. First cache hit. TTL usually 1 hour to 1 day.

Edge tier

Physically close to users. 100s of PoPs. First cache hit. TTL usually 1 hour to 1 day.

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Regional tier

10-20 large caches. Aggregate misses from edges. Hit rate higher than any single edge.

Origin shield

Single origin-facing cache. Every request from every region passes through. Multiplicative reduction on origin load.

Push vs pull

Pull: lazy fill on first request. Push: pre-warm hot content. Combine for launches.

Purge strategy

Content update? Purge propagates through tiers. Fastify → regional → edge. Takes seconds to minutes.

Three-tier cache hierarchy reduces origin load by 10-100x. Origin shield is the killer feature.