How We Cut API Response Time from 2.3s to 180ms Using Redis + Smart Caching

p95 latency dropped from 2.3 seconds to 180 milliseconds. Same hardware, same database, same traffic. The only thing that changed was how we cached — and I don't mean slapping @lru_cache on a function. I'm writing this because every Redis caching tutorial I read before this project showed me the same 15-line example: redis.get(key) or fetch_from_db() . That code works in a notebook. It will absolutely wreck you in production the first time real traffic hits it. This is the layered strategy that