Practice — Design a Chat System (WhatsApp / Slack / Messenger) (5 questions)
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Estimating the Connection Server Fleet Permalink →
A chat product has 300 million DAU. At peak, 25% of DAU are simultaneously connected via WebSocket. Each connection server can hold 600,000 concurrent idle connections.
- How many concurrent connections must the system support at peak?
- How many connection servers are needed (add a 30% safety margin)?
- What resource typically becomes the bottleneck per server before CPU does, and what is the practical fix?
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