Design a Global Cache for Small Images

Design a global small-image caching service backed by a fixed single database and serving hundreds of thousands of requests per second. Cover reads, updates, cache hierarchy, refresh or invalidation, and failures while allowing brief staleness. Requirements Design a global service that serves small images. Support hundreds of thousands of image requests per second across multiple regions. Keep the read path highly performant through an explicit cache hierarchy. Support images being updated in the backing database. Define a cache invalidation or refresh mechanism; serving stale images for a short period after an update is acceptable. Explain failure handling for the database and every cache layer. Notes The service is backed by a single database. Treat that as a fixed constraint rather than redesigning the source of truth. Make the freshness trade-off explicit: brief staleness is allowed, so the design should explain how that allowance protects read latency and origin load.