Hard Design: Chat System (WhatsApp/Slack)
Alice is connected to Chat Server 1. Bob is connected to Chat Server 2. Alice sends Bob a message. How is it delivered?
— Tests your understanding of this concept.
Answer Options
A Alice's server sends directly to Bob's server via HTTP
B Message is stored in DB, Bob polls for new messages
C Message is published to shared Redis Pub/Sub channel, Bob's server is subscribed
D A centralized router server handles all cross-server delivery
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