OLEKSANDR
IZOTOV

Commissioned work, in production since April 2026 and used daily. A full-stack educational platform built from scratch for a tutoring centre serving 200+ students. Java 21 and Spring Boot 3.5 behind JWT auth, PostgreSQL 16 under Flyway, self-hosted MinIO for files, and two separate rendering paths so the public pages are indexable. Replaces fragmented manual coordination with a unified system for scheduling, materials, testing, and communication.

Operating-room scheduling, built solo from scratch and running live — sign in with a demo account and move a booking. A Postgres EXCLUDE constraint makes overlapping bookings impossible to insert at all, so the guarantee survives two people clicking at once; Server-Sent Events push every change to open dashboards. Auth is self-hosted end to end: Argon2id, WebAuthn passkeys, Redis sessions, no external provider. 29k lines of Kotlin and SvelteKit under 187 tests.

A private VPN service, built as a distributed system rather than a box with WireGuard installed on it. An agent runs on every node with a six-operation contract, listening only inside a management tunnel — from outside its port does not exist. A separate control plane holds the database, polls the agents and runs the Telegram bot people use. It deliberately stays out of the traffic path: take it offline and the VPN keeps working. 260 tests across both halves.