This week in caching: edge cache vs origin cache — not either/or

This week in caching: edge cache vs origin cache — not either/or

The framing that fixes muddled cache strategies:

— Origin cache (Varnish/FastCGI/object cache) protects your database and app server. It's where personalized-but-cacheable fragments and TTL logic live.
— Edge cache (CDN PoPs) protects your origin from distance and volume. It's where truly anonymous, identical responses should terminate so requests never reach your box.
— The mistake: caching only at one layer. Edge-only means a purge or cache-miss storm hammers a naked origin; origin-only means every user still pays the network RTT to your single datacenter.

Layer them: long edge TTL for static + anonymous HTML, shorter origin TTL with tag-based purge underneath as the safety net.

Bookmark: Fastly's 'multi-tier caching' explainer — the mental model of cache as concentric shields.