Design a cross-region event processing platform
Company: Capital One
Role: Software Engineer
Category: System Design
Difficulty: medium
Interview Round: Onsite
## Scenario
Design a **cross-region event processing platform** that ingests events from producers, stores them durably, and delivers them to multiple consumers for processing.
## Requirements
- Producers send events continuously from multiple regions.
- Consumers (in one or more regions) subscribe to event streams and process events.
- Must support:
- **Durability** (events should not be lost)
- **Scalability** (high throughput)
- **Cross-region replication** / disaster recovery
- **Ordering guarantees** (at least per key/partition)
- **Retries and backpressure**
- Handling **duplicates** (at-least-once is acceptable if dedup is possible)
- Operational needs:
- Monitoring, replay, dead-letter queues, retention policies
## Deliverables
Describe:
- Public API for producing/consuming events
- Storage/log architecture and partitioning
- Cross-region replication strategy
- Delivery semantics (at-most/at-least/exactly-once) and how you achieve them
- Failure handling (region outage, consumer lag)
Overview: This question evaluates a candidate's expertise in distributed systems and event-driven architecture, covering competencies such as durable storage, partitioning and ordering guarantees, cross-region replication, delivery semantics, retries/backpressure, duplicate handling, and operational concerns like monitoring, replay, and dead-letter queues.
