How do you design a distributed event-driven architecture with guaranteed message ordering?

Guaranteed ordering in distributed systems is achieved through partitioning, key-based routing, and single-consumer per partition models.

In distributed reactive systems, global ordering is impossible at scale, so ordering guarantees are typically enforced per key or partition. Systems like Kafka ensure ordering within a partition. Reactive architectures preserve order by routing related events (e.g., per user/order ID) to the same processing lane. This avoids race conditions while maintaining scalability.