Oleksii

Oleksii Khamutinnikov
Senior Full-Stack Engineer · Project-Level Tech Lead · React, Node.js (NestJS), PostgreSQL
Kyiv, Ukraine (remote) · [open contact info](look above in the "contact info" section) · [open contact info](look above in the "contact info" section)
GitHub: https://github.com/mesh86lv
LinkedIn: [open contact info](look above in the "contact info" section)
HackerRank: https://hackerrank.com/profile/mesh86lv

SUMMARY
Senior full-stack engineer with 15+ years in software development, 9+ years of React and 6+ years of Node.js/TypeScript (NestJS).
Now on an e-commerce platform for 20+ EU countries (~1,000 RPS average, ~2,500 peak). First engineer on the Teapplix React
migration, UPShipper and Salespy: architecture, database design, billing, frontend. Project-level tech lead on UPShipper and
Salespy, now a hands-on senior engineer; helped grow the Teapplix team to 7-9 developers. Uses AI-assisted workflows: code
review (~30% faster reviews), sandboxed coding agents, Figma-to-code tooling.

TECHNICAL SKILLS
• Frontend: React 18, React 19, custom hooks, Next.js (App Router, RSC, SSR, SSG), TypeScript, JavaScript, Vite, Webpack, Redux
Toolkit, MobX, Zustand, TanStack Query, Zod, Tailwind CSS, shadcn/ui, Ant Design, Material UI, i18next, WCAG accessibility
• Backend: Node.js, NestJS, Express, TypeORM, Sequelize, REST, GraphQL, WebSockets, Server-Sent Events (SSE)
• Databases: PostgreSQL with PgBouncer, MySQL, Redis; primary-replica replication, sharding, indexing and query tuning
(EXPLAIN ANALYZE), versioned migrations
• Architecture: microservices, event-driven architecture (EDA), Clean Architecture, Domain-Driven Design (DDD), Saga
(orchestrator and choreography), Transactional Outbox, lightweight CQRS, Zero-Trust
• Queues and messaging: BullMQ, RabbitMQ, gRPC (Protocol Buffers)
• Security and compliance: JWT access/refresh rotation, 2FA, mTLS, rate limiting, CSRF/XSS mitigation, webhook signature
validation, PCI-DSS-aware design, GDPR erasure (anonymization), hash-chain audit logging
• Observability: Prometheus, Grafana, OpenTelemetry
• Infrastructure and CI/CD: Docker, Docker Compose, NGINX, Traefik (rate limiting, Coraza WAF middleware), AWS (EC2, S3,
Lambda, SNS, SQS), DigitalOcean, Bitbucket, GitHub Actions
• Testing: Jest, Supertest, Playwright, React Testing Library
• AI and automation: Claude Code, GitHub Copilot, Pi coding agent, Atlassian Rovo (AI code review), Figma API tooling, Model
Context Protocol (MCP), agent sandboxing (bubblewrap), n8n
• Leadership: code review, onboarding, mentoring, hiring interviews, technical roadmapping, feature prioritization, Agile/Scrum
facilitation

PROFESSIONAL EXPERIENCE

Ksisters
Senior Software Engineer · May 2025 - Present
European e-commerce platform: 20+ EU countries, ~1,000 RPS average, ~2,500 RPS peak. Hands-on senior engineer in a 7-engineer
team; code review and onboarding of new team members.
Stack: Node.js, Express, TypeScript, Sequelize, MySQL, Redis, BullMQ, React, Redux, MobX, Bitbucket, DigitalOcean, n8n
• Found a single-database bottleneck under heavy cron-job load; proposed and shipped primary-replica replication with ORM-
level (Sequelize) read/write splitting, making the platform faster and more stable.
• Cut the initial JavaScript bundle by 35% (Lighthouse CI), improving INP and LCP; fixed mobile lag in map rendering and split
monolithic frontend state into modular Redux/MobX, removing memory leaks.
• Designed and began rolling out Redis-backed BullMQ queues (priority lanes, retry policies, concurrency limits) to replace
overloaded cron jobs (the legacy scheduler ran 60+ jobs: marketplace feeds, notifications, promos, loyalty, recommendations).
• Introduced versioned, rollback-safe database migrations as the team standard, replacing SQL files in PRs; fixed index
mismatches and N+1 query patterns.
• Built background sync pipelines with external e-commerce services and contributed to the design of an event-driven
architecture.
• Implemented a SHA-256 hash-chain audit log with GDPR erasure as anonymization (IDs stay, values are replaced), so erasure
never breaks the chain; separated sensitive data, added encryption, isolated containers and networks.
• Designed the frontend testing setup (Jest, React Testing Library, Playwright) and localized the frontend for 20+ country sites
(local language, English, Ukrainian).
• Improved delivery: staging environments and tighter PR protocols shortened PR-to-deploy time; AI-assisted code review
(Atlassian Rovo) with PR templates in CI cut review time by ~30%.
• Built Figma API tooling (component schemas to JSON for AI-assisted code generation) and n8n automations (Telegram bot, Jira
API, Google Drive, AI steps) with automated engineering-metrics reporting.

Salespy
Senior Software Engineer (Founding Engineer, Sole Architect) · Feb 2024 - May 2025
Price-tracking SaaS for major marketplaces and retailers (Amazon, Walmart, Target, Home Depot), prices refreshed 4× daily. Started
as an independent prototype in late 2023, full-time from Feb 2024; owned backend, frontend, infrastructure, security and product
delivery end-to-end.
Stack: NestJS, TypeScript, PostgreSQL, Redis, RabbitMQ, BullMQ, Next.js, React, Docker, Traefik, GitHub Actions, Prometheus,
Grafana, OpenTelemetry, Puppeteer, AWS Lambda, S3, SNS, SQS, FastSpring
• Designed and built the product from scratch as first engineer and sole architect: NestJS microservices (RabbitMQ, BullMQ),
PostgreSQL schema and indexes, API, SPA frontend and infrastructure.
• Integrated FastSpring subscription billing: signature-verified webhooks and idempotent processing prevent duplicate charges;
Saga (choreography) with compensating actions plus Transactional Outbox keeps subscription state consistent under partial
failures, backed by an immutable audit log.
• Built a Puppeteer-based price-collection pipeline resilient to anti-bot protections (CAPTCHA handling, IP rotation) for Amazon,
Walmart, Target and Home Depot, normalizing price data.
• Launched ~3 months earlier on third-party price data while the in-house parser was built; the parser later removed that data
cost.
• Replaced the microservice that ingested third-party price files (JSON/CSV) with a serverless pipeline (AWS Lambda, S3, SNS,
SQS), triggered daily by a webhook.
• Scaled data: PostgreSQL sharded by marketplace domain with primary-replica read routing for analytics; Redis caching of shared
product data with distributed locks against cache stampedes.
• Chose SSE over WebSockets for one-way price streaming; eliminated N+1 queries through schema and query optimization.
• Secured access: JWT access/refresh rotation (15-minute access tokens, HTTP-only refresh tokens), Redis token blacklist, 2FA;
moved the edge proxy from NGINX to Traefik with two-tier rate limiting (edge + application), IP blacklisting against DDoS and
brute-force attempts, and a baseline Coraza WAF middleware.
• Moved the public part of the frontend from the SPA to Next.js (SSR for SEO); kept CLS under 0.05 on data-dense dashboards;
built a component library on shadcn/ui with shared design tokens.
• Defined the technical roadmap and prioritized features, later working alongside up to 3 peer engineers who joined; added demo
access after customer feedback showed many potential users dropping off at launch, shipped ahead of plan.

Teapplix Inc
Senior Software Engineer · Sep 2017 - Jan 2024
E-commerce operations platform: order and shipping management with carrier integrations.
Stack: React, JavaScript, REST API, MySQL, Perl/PHP (legacy platform)
• First React engineer on a legacy Perl/PHP platform; led the migration to a React SPA and designed the REST API and data-
transformation layers for it.
• Rebuilt client-side data handling (normalized state, efficient structures), removing rendering lag on data-dense tables with large
order volumes.
• Kept shipping-label UI workflows compliant through annual carrier certification cycles, including FedEx.
• Ran hiring interviews, onboarding, offboarding and mentoring (core group of up to 3, including an intern) as the team grew to 7-
9 developers.
• May 2022 - Jan 2024 (after UPShipper was paused): new feature development, optimization and bug fixing on the main
platform.
Project: UPShipper (at Teapplix)
Project-level Tech Lead and Architect · Dec 2020 - May 2022 (paused in 2022 due to the war in Ukraine)
B2B logistics SaaS for the European market: marketplace integrations (Amazon, eBay, Allegro, WooCommerce), warehouse and
inventory management, bulk shipping labels, live background-job dashboards. Started development as the first engineer.
Stack: Node.js, NestJS, TypeScript, TypeORM, MySQL, Redis, RabbitMQ, BullMQ, gRPC, NGINX, AWS EC2, GitHub Actions,
Prometheus, Grafana, OpenTelemetry, React, Next.js
• Designed the architecture and ran the project from kickoff to production, evolving an Express prototype into NestJS
microservices (TypeORM) with Clean Architecture and DDD applied where the domain called for it.
• Defined the technical roadmap and prioritized features; worked alongside up to 3 peer engineers as the team grew.
• Zero-Trust groundwork (partial) for planned card payments: dedicated service networks, mTLS between services (gRPC/HTTPS),
per-client database isolation; designed with PCI-DSS requirements in mind.
• Access control: JWT rotation with blacklist, 2FA, IP blacklisting, NGINX rate limiting.
• Payments: Saga (orchestrator) with compensating actions plus Transactional Outbox (BullMQ, RabbitMQ) for consistent multi-
service transactions; immutable audit log of critical operations.

• Data: MySQL primary-replica with ORM-level read/write routing, Redis caching, lightweight CQRS (reads started on the same
tables, structured to split later); fixed slow queries with EXPLAIN ANALYZE.
• Built integrations with Amazon, eBay, Allegro and WooCommerce APIs (webhook signature validation, idempotent processing)
with exponential backoff and circuit breakers.
• Built logistics dashboards and a bulk shipping-label wizard (React, Next.js) with SSE for live background-job status; replaced
heavy Ant Design usage with an internal component library.
• Cut local and pipeline build times by ~90% through Webpack optimization (persistent caching, parallel builds, minimizer tuning,
faster dev source maps); added Docker Compose multi-stage layer caching to speed up pipeline builds.

AI-ASSISTED ENGINEERING
• AI-assisted development with Claude Code, GitHub Copilot and the Pi terminal coding agent: reusable role-specific prompts
(architect, code review, debug, security review, test engineer and others).
• Built a bubblewrap sandbox so coding agents run with restricted access; set up MCP servers and custom agent extensions.
• Plan-first workflow: every AI-generated step is validated before it ships.

EARLIER EXPERIENCE (2010-2017) - FULL-STACK AND PLATFORM ENGINEER
• Ford web applications (Ford-Retail, Ford-Showroom, Ford-Build&Price) at DevFactory in Java/JavaEE and JavaScript; AWS
automation with CloudFormation and Chef.
• ERP systems for Tele2, KM-Ware and Nutrilogic on the Aprentis low-code PaaS (C#, VB, MSSQL); internal React documentation
portal (Redux, Material UI).
• At Pervasive, delivered a Java data connector between MS Access and Oracle CRM On Demand, coordinating a small cross-
functional group; also built an Android app (Java) for audio capture and cloud upload.

EDUCATION
Master of Science in Computer Science - Zaporizhzhya State University, 2005-2010

LANGUAGES
English: B2 (Upper-Intermediate) · Ukrainian: Native