Your single-server key–value store must scale across many servers. Propose a design using consistent hashing to partition keys. Explain client/gateway routing, use of virtual nodes, how node joins and leaves trigger minimal data movement, and how you handle rebalancing. Define replication strategy and quorum choices, read/write paths, failure detection, re-replication, and recovery. Address hot keys, skew, and load balancing, as well as data migration safety, monitoring, and rolling upgrades. Compare alternatives (e.g., directory service, range partitioning) and justify trade-offs.