This week in caching: cache your failures too

This week in caching: cache your failures too
Three on negative caching — the cheap win nobody configures.
— cache 404s briefly — a flood of requests to a missing URL otherwise hammers origin every time; proxy_cache_valid 404 1m; in nginx absorbs it.
— cache 5xx with care — short TTLs on errors plus stale-if-error keep a wobbling backend from a death spiral; don't cache them long or you bake in the outage.
— DNS negative caching (NXDOMAIN) — the often-forgotten layer; misconfigured SOA minimum TTL means typo'd lookups keep slamming resolvers.
Bookmark: nginx's proxy_cache_valid per-status reference — five minutes of config, real origin relief.