Dung

Junior Java Backend Developer

Saltlux • Vollzeit

Sep 2025 - Present • 1 yr 1 mo

Backend engineer on a microservice platform that delivers mobile push notifications and powers the in-app notification centre. What I built and own: - Kafka batch consumers that ingest content notification events, deduplicate them and bulk-write metadata to MongoDB, with manual offset commit so a batch is acknowledged only after a successful write - no silent message loss. - An asynchronous delivery layer running on dedicated worker pools, which separates push delivery from ingest so provider latency never slows down consumption. Delivery to FCM for Android and APNs for iOS, with per-device result handling. - A per-user push policy engine: master switch, timezone-aware quiet hours and per-category preferences, backed by a Redis cache over MariaDB with fail-open defaults. - Badge counting in Redis, reserved per batch and confirmed on delivery, keeping unread counts consistent across a user's devices. - Staged failure recording and a retry scheduler with an attempt limit and a permanent-failure state, covering database-insert, push-delivery and real-time-publish failures. - Real-time in-app and web delivery through Redis publish/subscribe with a WebSocket bridge. - REST APIs for device registration, notification listing, read and viewed state, and user push settings. Stack: Java 17, Spring Boot 3, Apache Kafka, MongoDB, MariaDB, Redis, FCM, APNs, OpenFeign, Docker, GitLab CI, ArgoCD.