Code Room
System designMedium
Question
Design the WebSocket layer for a live stock-and-crypto price service that pushes tick updates to ~2 million concurrent browser/mobile clients, where each client subscribes to a personal watchlist of symbols and must see updates within ~250ms. Cover how you scale connections across many gateway nodes, how a client's subscriptions get the right ticks, what happens on a flaky-network reconnect, and how you avoid hammering slow clients.
What a strong answer looks like
Clarify scale and constraints first. Propose a clean component breakdown, then go deep on the hard parts — data model, bottlenecks, consistency, failure modes — and name the trade-offs you are making.
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