System Design Problem

Design a User Presence System

Commonly Asked By:SlackWhatsAppMicrosoftDiscord

  • Show online status: Green dot for active users
  • Show last seen: "Last seen 5 minutes ago"
  • Real-time updates: Status propagates to friends within 5 seconds
  • Typing indicator: "Alice is typing..." in chat
  • Privacy controls: Hide status from specific users
  • Multi-device: Online on any device → online
  • Idle detection: Mark "Away" after 5 min inactivity
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