Design a notification and fan-out system that delivers to millions of users across push, email, and SMS.
A celebrity posts and 50M followers need a notification. The tricky parts are not sending one message; they are fan-out strategy, deduplication, channel routing, and not flooding users. Here is the architecture that handles both the long tail and the viral spike.
Updated Sep 2026 · Grounded in real GenAI, LLM, and AI/ML engineering interview loops and written to a senior-engineer editorial bar.
A celebrity posts and 50M followers need a notification. The tricky parts are not sending one message; they are fan-out strategy, deduplication, channel routing, and not flooding users. Here is the architecture that handles both the long tail and the viral spike.
Lead with where the obvious approach breaks, because that is the judgment they are screening for — most candidates jump straight to the happy path and lose the room.
Then walk the failure back through the pipeline in order, naming the one metric the customer's exec sponsor actually cares about before you propose the fix.
