Design a Multi-Region Database

Requirements

• •Accept writes in any region and replicate to all other regions asynchronously
• •Detect and resolve write conflicts when the same record is modified concurrently in two regions
• •Guarantee that EU user data is never replicated outside the EU region
• •Provide a global secondary index queryable from any region with eventual consistency
• •Ensure schema migrations can be applied rolling-forward across all regions without downtime

Non-Functional Requirements

• •Local region write latency < 10ms (p99)
• •Cross-region replication lag < 500ms under normal conditions
• •Conflict resolution: < 1% of writes result in conflicts
• •System remains available in each region even during cross-region network partition

Constraints

• •3 target regions: US-East, EU-West, AP-Southeast
• •Each region must accept writes (multi-master) to minimize cross-region write latency
• •Data residency: EU user data must never leave the EU region (GDPR compliance)

Evaluation Criteria