MQTT, Kafka, time-series storage, consumer design, and load tests that check the final stored result—not just queue health.

Parsers, layout engines, stable IDs, snapshot tests, and one-way data flows with explicit layer boundaries.

Authentication, payments, async workers, caching, monitoring, recovery paths, and security-conscious API design.

PDF-to-exam service in a live pilot, registered under an academy's business license. Built with an academy teacher: I handle most development and server operations and review the teacher's code before merging. I fix issues from real user feedback, and review logs weekly. Visit service ↗

FastAPI Redis/RQ workers PostgreSQL

A hold-and-ledger model with request-ID idempotency and bounded retries keeps failed jobs from double-deducting or silently dropping questions.

Vehicle telemetry pipeline: MQTT → Kafka → InfluxDB/PostgreSQL, with anomaly consumers and a DLQ.

Spring Boot Kafka fault injection

Measured a 72.1% message loss in one run of a 90-second broker outage, then observed zero loss in three repeat runs after the fix.

_{Simulated data on a single host. Limits are documented in the repository.}

Lodging reservation platform split into user, host, and admin apps over one 30-table schema. Live demo ↗

Spring Boot JPA Toss Payments

Team lead of three: built the 65-endpoint User API and React client, then hardened IDOR and privilege checks after the bootcamp.

_{Free-tier hosting — the first load may take up to a minute.}

On-device smart home hub that learns habits from real usage, asks first, and automates only what the user hands over. Finalist, Embedded SW Contest (smart appliance track).

on-device AI Raspberry Pi ESP32

Fine-tuned model: 30 → 38 correct on 42 unseen sentences. Gantry return error 0.05 mm on hardware.

_{Accurate physical button presses and the full closed loop are not yet verified.}