Built an async, fault-tolerant notification platform with RabbitMQ-based delivery, retry and DLQ handling, real email and SMS delivery, campaign-based bulk sending, dynamic audience segmentation, and Prometheus/Grafana observability.

A backend payment system built to handle failures, duplicate requests, and concurrent transactions using the Transactional Outbox Pattern, Redis Lua scripting, database-level idempotency, retry + DLQ, and distributed scheduling with ShedLock.

A Spring Boot URL-shortening service with Base62 short codes, Redis caching, and Kafka-based asynchronous click tracking. Supports URL expiry, soft deactivation, validation, and click statistics.

A real-time terminal chat application using gRPC bidirectional streaming, supporting multi-client messaging, private messages, and multiple chat rooms with thread-safe client and room management.