Start by clarifying requirements and constraints, then propose a high-level architecture that decouples synchronous client interactions from asynchronous exchange events using an event-driven design. Walk through the order lifecycle, failure scenarios, scalability, and consistency mechanisms, and finish with API design and observability considerations.
Pro tip: Emphasize idempotency and reconciliation: use client-provided order IDs to deduplicate requests and implement a periodic reconciliation job to detect and resolve discrepancies between internal state and exchange state.
Ask about expected throughput, latency SLAs, supported exchanges, order types, and consistency requirements. Confirm that the synchronous API is only for order submission, while fills/cancellations are asynchronous.
Propose an event-driven architecture with an API gateway, order service, message queue (e.g., Kafka), and exchange adapters. Use a database for order state and a cache for fast lookups.
Outline states: PENDING_NEW, NEW, PARTIALLY_FILLED, FILLED, PENDING_CANCEL, CANCELED, REJECTED, EXPIRED. Describe transitions and how to handle failures like timeouts, partial fills, and exchange errors with retries and dead-letter queues.
Discuss partitioning by client or symbol, autoscaling, and backpressure. For consistency, use idempotent operations, optimistic locking, and eventual consistency with reconciliation. For multi-exchange, implement a routing layer with smart order routing logic.
Define REST endpoints for order submission, cancellation, and status queries, plus WebSocket for real-time updates. Include metrics, logging, tracing, and alerting for monitoring system health and order flow.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.