Edge Cache and CDN Platform  ·  View 18 of 29  ·  5 · Runtime

Freshness Classes by Origin State

What a strict, standard or resilient path serves when the origin is healthy, slow, down, or when the PoP itself is overloaded.

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Fresh in cache Stale · origin healthy Origin slow Origin down PoP overloaded strict Serve hit Revalidate first 304 or 200 Wait ≤ 10 s then error page Declared error page never stale Serve hits revalidation kept standard Serve hit Serve stale refresh behind · ≤ 60 s Stale inside window Error after window Stale · refresh deferred resilient Serve hit Serve stale refresh behind Serve stale stale-if-error Serve stale ≤ 24 h labelled Stale · no refresh negative (404 · 410) Serve cached 404 ≤ 60 s Refetch Serve cached 404 Declared 5xx · 5 s stops a retry storm Serve cached Freshness Classes — What Each Path Serves in Each Origin State Overload sheds bypass traffic first, then low-priority properties, then revalidation. Every stale response is labelled in Cache-Status. v 1.0 · owner Edge Platform · date 2026-09

Decisions

  • The choice between a wrong answer and no answer belongs to the property owner and is made before the incident. A strict path never serves stale. A resilient path serves stale for up to 24 hours, labelled.
  • Staleness bounds are the platform's, not the origin's. An origin that sends stale-if-error of a week gets the class maximum.
  • A slow origin is not a down origin. Slow is judged against the origin set's declared threshold and handled with waiting and ceilings; down is judged on errors and handled by the freshness class and endpoint failover.

Shedding order under overload

  • First bypass and uncacheable traffic, because serving it costs an origin fetch. Then low-priority properties by declared class. Then revalidation, so the cache keeps answering from what it has. Cache hits are the last thing shed.

Numbers

  • Stale-while-revalidate window of 60 s by default for standard; negative cache 60 s for 404 and 410; declared 5xx classes cached 5 s, which is enough to stop a retry storm and short enough to be harmless.
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Solution Architecture v1.0 · Edge Architecture · 2026-09 · 29 views · open source, fully on-premises18-freshness-by-origin-state