Event-Driven vs Request-Response Architecture for UK Software — Honest Comparison (2025)
Request-response (REST APIs) is right for most UK software: simpler, easier to debug, easier to audit for FCA/NHS compliance, and appropriate for most transactional workloads. Event-driven architecture (Kafka, AWS EventBridge, SNS/SQS) is genuinely better for: high-throughput data pipelines, audit trail requirements (every event immutably logged), microservices needing loose coupling, and real-time data streaming. Do not adopt event-driven architecture prematurely. Event-driven architecture has become fashionable in UK software development. Here is an honest assessment of when it genuinely improves a system versus when it adds complexity without benefit.
| Factor | Request-Response (REST) | Event-Driven (Kafka/EventBridge) |
|---|---|---|
| Debugging | ✅ Simple — trace request through system | Complex — trace events across consumers |
| FCA audit logging | ✅ Easy — log each request/response | Events are the audit log — excellent once implemented |
| UK GDPR right to erasure | ✅ Delete from database | Must propagate erasure event + confirm from all consumers |
| Latency | ✅ Low — synchronous | Higher — async processing |
| Throughput at scale | Limited by synchronous chain | ✅ Excellent — consumers scale independently |
| Data pipelines | Not appropriate | ✅ Excellent (Kafka) |
| Microservices coupling | Tight (knows endpoint) | ✅ Loose (knows event schema) |
| Testing complexity | Low — unit + integration tests | Higher — consumer contract testing needed |
| ClickMasters default | All transactional workloads | Data pipelines, audit trails, high-throughput microservices |
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