System designHardsd-g234

Subject MultitenancyLevel Senior–Staff~45 minCommon in Distributed systems interviewsIndustries Technology

Question

Design a cell-based (sharded-by-tenant) architecture for a SaaS platform serving 1M tenants, where the goals are: limit the blast radius of any failure to a small fraction of tenants, route every request to the correct cell with minimal latency, and migrate a tenant from one cell to another (rebalancing, or moving a growing tenant to a dedicated cell) with near-zero downtime. Walk through how tenant→cell mapping works and is looked up, how you keep the router fast and correct, and how a live tenant migration avoids split-brain.

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.