A notification system often starts with a simple requirement: send an email, text message, or push notification when something happens in an application. For a small system, calling an external provider directly may be enough. As traffic grows, however, notification delivery becomes a distributed systems problem. A production notification platform needs to handle traffic spikes, provider failures, duplicate events, retries, delivery tracking, and multiple notification channels without slowing down the application that generated the notification.
This article explores how a scalable notification system can be designed using Spring Boot and Kafka, with a focus on asynchronous processing, fault tolerance, idempotency, retries, and horizontal scaling.