Oleksandr

OLEKSANDR ANTONIUK
Senior Backend Engineer
Node.js / TypeScript · Backend, Infrastructure & AI Tooling
Ukraine, Vinnytsia region · [open contact info](look above in the "contact info" section)
[open contact info](look above in the "contact info" section)
[open contact info](look above in the "contact info" section) · t.me/underground_alex

SUMMARY
Backend engineer specializing in Node.js and TypeScript. I design multi-tenant SaaS architectures and complex
APIs, own platform authentication, authorization and service-to-service contracts, and handle billing across
mobile IAP and web payment providers.
Beyond conventional backend work, I ship AI features into products and build my own AI tooling, including a
published MCP server for semantic code search, and I run agentic AI as a standard part of the daily development
workflow.

SKILLS
– Backend: Node.js (NestJS, Express), TypeScript, REST, GraphQL, WebSockets (Socket.IO)
– Architecture: SaaS multi-tenancy, DDD, Event-driven, BullMQ, RabbitMQ
– Data: PostgreSQL (incl. pgvector), MongoDB, Redis, TypeORM, Prisma, Drizzle
– AI Tooling: Agentic development (Claude Code, MCP), local RAG (Ollama, Infinity)
– Integrations & Auth: Stripe, LiqPay, App Store / Google Play IAP, LTI, Auth0, OAuth2/JWT
– Infrastructure & CI/CD: Docker, Kubernetes API, Traefik, GitHub Actions, Bitbucket Pipelines, AWS (S3, SES),
Hetzner, HashiCorp Vault
– Quality & Observability: Jest, Vitest, Sentry
– Also: React, Next.js · Reverse engineering, microcontrollers, embedded systems

EXPERIENCE
Backend Engineer · FlexReality Sep 2024 – Sep 2026
Development of an EdTech SaaS platform and internal AI tools
– Owned feature delivery end-to-end across the platform’s GraphQL, REST and Socket.IO surfaces, serving the
web app and the Unity-based whiteboard and mobile clients: requirements into technical decomposition,
implementation, coordination across teams, validation against acceptance criteria. 10+ features shipped over 2
years via staging, feature flags and controlled releases.
– Built LTI integrations connecting the platform to Moodle and to national Ukrainian school systems (NZ.UA,
HUMAN), including single sign-on through the LTI launch flow.
– Redesigned platform authentication and authorization: replaced a 473-line global Express middleware with
declarative per-route policies over a typed policy union and an exhaustive dispatcher, making an unhandled
policy a compile error instead of a production hole. ~316 explicit route policies across 172 files.
– Rebuilt service-to-service auth on a canonical header contract with a compile-time-validated key registry,
timing-safe comparison and per-route caller allow-lists; cut over four services across two regions in a single
release rather than leaving a dual-format window open.
– Extracted cross-platform billing into a standalone service and extended subscription logic across native IAP
(App Store, Google Play), Stripe and LiqPay, including provider webhook handling, idempotency and
subscription state reconciliation.
– Modernized the legacy codebase: platform-wide logging refactor, Sentry for production error tracking, and
backend i18n with an external translation service.
– Shipped an in-product AI assistant with a frontend engineer: OpenAI integration with tool calling behind a
library of built-in prompts for lesson preparation and formula generation, plus image generation from an
in-house model on a dedicated server.
– Built the local RAG code-search system used for cross-repository context retrieval, published as
codesearch-mcp (see Projects); introduced agentic AI tooling (Claude Code) into the team workflow, reviewed
backend code and onboarded engineers.

Software Engineer · Maven Group Jan 2024 – Jun 2024
Kubernetes cluster and resource management platform
– Developed full-stack (React/Node.js) Backstage.io plugins for managing Kubernetes clusters and their
resources, deploying cluster objects programmatically via the Kubernetes API.
– Implemented RESTful APIs connecting the plugins with Kubernetes and ArgoCD to automate image creation
from GitHub.
Solution Architect / Software Engineer · Rist School Apr 2023 – Jan 2024
Multi-tenant CRM platform for education
– Sole engineer carrying the product: architecture, backend, infrastructure and deployment of a multi-tenant
CRM built from a blank repository (NestJS, Next.js, PostgreSQL, AWS S3 and SES, HashiCorp Vault).
– Made and executed the core design calls (tenancy model, data isolation, auth) and covered the frontend where
delivery required it.
– Ran the delivery cycle end to end: business and system analysis, requirements into technical tasks, CI/CD on
Bitbucket and deployments across environments.
Node.js Developer · QATestLab Jan 2022 – Feb 2023
– Built a corporate Skype bot (Node.js, TypeScript, Microsoft Bot Framework) integrated with internal company
systems, automating internal workflows and daily team communication.
Node.js Developer · BezBrendu Jan 2021 – Oct 2021
Development of a CRM system for online sales
– Engineered a custom SDK for the Facebook and Instagram Marketing APIs handling external data
synchronization, alongside server-side logic and RESTful APIs in Node.js.
– Designed relational schemas (MySQL) and scripted Auth0 tenant synchronization for permissions and roles.
Founder & Hardware Engineer · Portal Sep 2005 – Jan 2021
– Programmed and flashed microcontrollers, EEPROM and NAND memory; reverse-engineered proprietary
hardware and embedded systems to resolve low-level failures.

PROJECTS
codesearch-mcp npmjs.com/package/codesearch-mcp
– Published MCP server (npm) giving AI coding agents semantic search across local repositories: AST-aware
chunking via ts-morph, vectors in PostgreSQL + pgvector through Drizzle ORM, incremental re-indexing of
changed files.
– Model-agnostic embeddings: any local model pulled into Docker on demand or an external OpenAI-compatible
API, with optional cross-encoder reranking on any reranker model. Nine MCP tools beyond search (symbol
lookup, call sites, dependency graphs) and Nx monorepo support.
Fix Flow CRM multi-tenant SaaS for repair shops (in development)
– Multi-tenant backend on NestJS, GraphQL and Prisma: per-tenant data isolation, role-based access (owner /
admin / finance / client) and encrypted credential storage in PostgreSQL.
– Deployed as a single-host Docker Compose stack (Hetzner, Traefik, PostgreSQL, Redis) with a staging
environment.
– Domain knowledge comes from fifteen years running a hardware repair business.

EDUCATION
Vinnytsia Technical College, Radio Engineering
Languages: English – Intermediate (B1) · Ukrainian – native