Design an Event Sourcing / CQRS System

Requirements

• •Store all state changes as immutable events in an append-only event store (stream-per-aggregate)
• •Rebuild aggregate state by replaying its event stream from the store
• •Maintain denormalized read models (projections) updated asynchronously from the event stream
• •Take periodic snapshots of aggregates to cap replay time
• •Support rebuilding a projection from scratch by replaying the full event log

Non-Functional Requirements

• •Event append latency < 10ms (p99)
• •Aggregate replay time: < 100ms for up to 10,000 events per aggregate
• •Projection update lag < 500ms from event commit
• •Event store must retain all events indefinitely

Constraints

• •Domain: an e-commerce order management system
• •Aggregates: Order, Product, Customer
• •System must support auditing: the complete history of every order must be queryable

Evaluation Criteria