Node.js Caching Patterns

Description

Add and review caching in Node.js services - the cache-aside pattern with invalidation on write, in-process caches (node-cache, lru-cache) and when per-pod copies are wrong, Redis with ioredis (TTLs, JSON serialization, retry and offline-queue settings, failing open when Redis is down), cache stampede prevention (in-process promise sharing, Redis locks with owner-checked release), invalidation strategies (TTL, delete-on-write, tag sets), HTTP Cache-Control, stale-while-revalidate and ETags, what must never be cached, and measuring hit rate. Use whenever the user adds Redis or a cache to a Node API, an endpoint is slow or hammers the database, the database falls over when a hot key expires, users see stale or someone else's data, or the user asks about TTLs, cache invalidation or HTTP caching headers.