What is a common drawback of event-driven architecture?

• A. It can introduce higher complexity due to decoupled components and asynchronous flows.
• B. It eliminates scalability.
• C. It guarantees exactly-once delivery in all cases.
• D. It always has lower latency than synchronous systems.

Answer: (D)

Event-driven design relies on asynchronous messages to connect parts of a system, so producers emit events and downstream components react without a direct call. This decoupling and asynchronicity bring real benefits—flexible scaling, responsiveness, and resilience—but they also introduce more complexity. Tracking end-to-end behavior becomes harder when components operate independently, and you must design for eventual consistency, potential out-of-order event delivery, retries, error handling, and idempotency. Debugging, testing, and observability across multiple services and the messaging layer require extra tools and discipline. The extra layers of routing, queuing, and handling failures mean more moving parts to manage.

Regarding the other statements: latency is not guaranteed to be lower in all cases—queuing and asynchronous processing can add latency, especially under load. Scalability is not eliminated; the pattern typically enables more scalable architectures by letting components scale independently. Exactly-once delivery in all cases is not guaranteed; many messaging systems offer at-least-once or at-most-once semantics, requiring careful design to avoid duplicates.