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OLEH BABIAK
Node.js Backend Engineer
+38 (050) 265‑92‑88 [open contact info](look above in the "contact info" section) Uzhhorod, Ukraine
[open contact info](look above in the "contact info" section) github.com/OlehBabyakOff

PROFESSIONAL SUMMARY
Node.js Backend Engineer with 4+ years of commercial experience building scalable, high‑load backend
systems. Solo redesigned and rewrote a multi‑country e‑commerce platform on NestJS, introducing queues,
caching, and a modular architecture, and built a case‑management platform with real‑time communication,
OCR, and vector‑based document search. Strong background in REST APIs, WebSockets, PostgreSQL, Redis,
cloud infrastructure (AWS), and payment integrations. Experienced in clean architecture, performance
optimization, and automated testing. Comfortable owning features end‑to‑end, contributing to architectural
decisions, and stepping into full‑stack work (React, Next.js) when needed.

PROFESSIONAL EXPERIENCE
Softlist | June 2026 – Present
Node.js Backend Engineer
E‑commerce platform (UA / PL / KZ)
Maintained and extended the legacy e‑commerce backend serving three country deployments from a
single codebase.
Solo redesigned the entire architecture and rewrote the project on NestJS + Fastify with TypeScript,
PostgreSQL, and a type‑safe ORM, keeping API contracts compatible with existing clients.
Introduced background job queues and caching, reducing response times and offloading heavy operations
(documents, exports, emails) from request handling.
Replaced per‑country branches and conditionals with country strategies, typed per‑country config, and
country‑scoped routes, schedulers, and migrations.
Built declarative access control (roles, permissions) and an automatic audit log; unified response format,
error handling, validation, and structured logging.
Implemented payments (Przelewy24), PDF generation, XLSX/CSV export, email templates, i18n
(UA/EN/PL/RU), GeoIP, reCAPTCHA, SEO, sitemap, and file storage.
Upgraded the toolchain to the latest NestJS/TypeScript, significantly speeding up builds, linting, and test
runs.
Set up unit, integration, and e2e testing against a real database, custom lint rules, pre‑commit hooks, and
CI/CD pipelines.
Took on full‑stack tasks with React and Next.js during high‑workload periods.
МКАС / МАК — arbitration case‑management platform
Developed the backend on NestJS + Fastify, PostgreSQL, Redis, and BullMQ with a separate worker
process for background jobs.
Implemented real‑time chats and notifications with Socket.io WebSocket gateways.
Built a document processing pipeline: OCR and layout parsing of scanned documents (PaddleOCR‑VL),
text chunking, and embeddings with multilingual‑E5.
Implemented document search: vector search in Qdrant combined with lexical search via rank fusion.

Built secure auth: cookie sessions, TOTP 2FA, brute‑force protection, rate limiting, security headers, input
sanitization.
Integrated Microsoft Graph calendars, Zoom video conferences, and S3‑compatible storage with
presigned URLs.
Built XLSX/CSV import and export as queued jobs, audit logging, and automated test coverage.
ThinkMobiles | September 2022 – February 2026
Node.js / Vue.js Engineer
Designed, developed, and maintained scalable backend services for video content creation, streaming, and
media processing platforms.
Built RESTful APIs and WebSocket services enabling real‑time communication between backend systems
and client applications.
Implemented payment systems using Stripe and PayPal, including subscriptions, secure transaction flows,
and webhook handling.
Integrated blockchain functionality for NFT‑based features using Solidity smart contracts, Web3.js, and
Ethers.js.
Improved system performance and scalability through Redis caching, query optimization, and modular
service‑oriented architecture.
Worked with multiple databases depending on project requirements: MongoDB (Native Driver, Mongoose),
PostgreSQL (Sequelize), and Redis.
Migrated existing projects from Express.js to Fastify, improving throughput and lowering response times.
Integrated Shopify into backend systems for e‑commerce workflows and external service synchronization.
Developed frontend functionality using Vue 3 and Nuxt 3 (SPA, SSR, SWR), collaborating closely with
designers and product managers.
Participated in code reviews, architectural discussions, and mentoring within the development team.

EDUCATION
Uzhhorod National University | August 2023 – December 2024
Master’s Degree in Information Technology
Uzhhorod National University | September 2020 – June 2023
Bachelor’s Degree in Information Technology

TECHNICAL SKILLS
Languages: JavaScript (ES6+), TypeScript, Solidity, SQL
Backend: Node.js, NestJS, Fastify, Express.js
Frontend: React, Next.js, Vue 3, Nuxt 3
Databases & Search: PostgreSQL, MongoDB, Redis, Qdrant (vector search)
ODM / ORM: Drizzle ORM, Sequelize, Mongoose
Queues & Caching: RabbitMQ, BullMQ, Redis
AI / Document Processing: OCR (PaddleOCR‑VL), text embeddings (multilingual‑E5)
API & Communication: REST APIs, WebSockets, Socket.io
Authentication & Security: JWT, OAuth2, session‑based authentication, 2FA (TOTP)
Cloud & Infrastructure: AWS (S3, Lambda, MediaConvert), MinIO, Docker, Docker Compose
CI/CD & DevOps: Bitbucket Pipelines, GitHub Actions, GitLab CI/CD, Nginx, PM2
AI‑Assisted Development: Claude Code, OpenAI Codex, GitHub Copilot, Cursor
Testing & Tools: Vitest, Jest, Supertest, Postman, Swagger / OpenAPI

Monitoring & Integrations: Datadog, Sentry, SendGrid, Shopify, Przelewy24, Stripe, PayPal, Microsoft Graph,
Zoom API, Telegram Bot API

ARCHITECTURE & ENGINEERING PRACTICES
Object‑Oriented Programming (OOP)
SOLID principles
Clean Architecture
Modular and service‑oriented backend design
Performance optimization and scalability best practices
Declarative cross‑cutting concerns: custom decorators, guards, pipes, interceptors (auth, roles,
permissions, audit log)
Unified API response format, centralized error codes, global exception filter
Schema‑first validation, type‑safe SQL, versioned migrations and seeds
Background job queues, worker processes, and caching; real‑time events via WebSocket gateways
OCR and text embedding pipelines for document search
Security hardening: 2FA, brute‑force protection, rate limiting, input sanitization
Unit, integration, and e2e testing; custom lint rules, pre‑commit hooks, CI quality gates
Incremental legacy rewrite with backward‑compatible API contracts

LANGUAGES
Ukrainian — Native
English — B2 (Upper‑Intermediate): technical communication, documentation, and daily collaboration