System designHardsd-g049

Subject Load balancingLevel Senior–Staff~45 minCommon in Databases & SQL · Networking & APIs · Algorithms & data structures interviewsIndustries Technology, Software development

Question

Design load balancing for a real-time presence/WebSocket service where each user holds a long-lived connection and is pinned to one server that owns their session state. You run thousands of servers, need even connection distribution, and must minimize how many users get disconnected when you add/remove servers during a deploy or autoscale event. Explain the routing scheme and how you handle a server dying mid-session.

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.

Learn the concepts

Narrate your design

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Run or narrate your approach, then ask the coach.