Cell-based multi-tenant routing
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.
Clarify5:00 left
Estimate5:00 planned
Design15:00 planned
Deep dive12:00 planned
Failure8:00 planned
Which questions mattered is sealed until you submit. Telling you now would just be handing over the edge cases.
Run or narrate your approach, then ask the coach.