Sergii Gulenok
Full-Stack Engineer · Front-End Tech Lead @ Amazon Fulfillment Technology
Luxembourg [email protected] LinkedIn GitHub gulenok.lu
Summary
~20 years turning complex problems into simple tools. Currently Front-End Technical Lead at Amazon in Luxembourg — React, TypeScript, micro-frontends, but the tech is secondary to whether users can get their job done without thinking about it.
Past lives: 3D dental CAD software, internal HR tools, independent consulting where I did product engineering before the term existed — talking to users, shaping requirements, shipping the thing. Production code in JS/TS, C++, C#, F#, Clojure, Java, Scala, Python — whatever the problem called for.
Lately interested in where AI actually helps engineers think better versus where it just produces more code faster. The distinction matters — most software problems are people problems in disguise, and no amount of generated code fixes a bad abstraction.
Experience
Amazon · Luxembourg
December 2020 – Present
Front-End Technical Lead — Fulfillment Technology (2024–present)
Own the front-end architecture for fulfillment tools. Complex operational workflows that need to feel simple — fewer clicks, less confusion, happier users. Multi-tenant platform, many teams shipping independently.
Full-Stack Senior Engineer — Worldwide Stores Finance Technology (2020–2024)
- Built a large-dataset analysis tool — user-friendly pivot tables over dozens of terabytes. Designed a custom query language (MongoDB-inspired) and a database definition language supporting context-aware fields, computed fields, and automatic join resolution. Generated optimized queries for Athena, Kylin, and StarRocks, routing to the optimal engine per use case. Used daily by 5,000+ finance and operations users worldwide for decisions that previously required a BI engineer to build custom dashboards for each case.
- EU Financial bridging tool — automated 65% of manual bridging effort for 400+ weekly users across 110+ EU warehouses. Voted #2 out of 41 bridging tools org-wide.
- Headcount management and requisition approval system — replaced fragmented PowerBI dashboards and manual processes across 110+ warehouses. Automated requisition checks gave back 6 hours/week to the central team; field managers called it a "life-changer."
Toptal · Remote
June 2020 – December 2020
Accepted into the Toptal network (top 3% screening). Worked on client projects bridging the gap before relocating to Luxembourg for Amazon.
Independent Consulting · Kyiv / Remote
November 2015 – December 2020
Independent consulting practice serving US and EU clients. No PMs, no dedicated infrastructure teams — pulled requirements directly from users, shaped the product, built it, shipped it:
- Grammarly — built the tools that ran their people operations: how trips got approved, how performance was reviewed, how promotions happened. No product manager — gathered needs directly from HR and managers, translated those into requirements, and delivered. Used by the entire company.
- US real-estate startups — sole engineer on the website and back office for a company among the top five online wholesale land marketplaces in the US. Wore every hat from customer interviews to deployment.
- Dentsply Implants — continued work on 3D dental CAD tooling (see below).
- InfoSec Institute — engineering and consulting.
Also mentored junior engineers into developers who could handle production systems without hand-holding.
Dentsply Implants n.v. · Kyiv
Senior Software Engineer · Kyiv · Apr 2015 – Feb 2016
Returned to hands-on engineering by choice.
Part of a 3-person team building two medical software products: a 3D CAD system for dental technicians (released 2015, still in production use) and the scan processing tool for the Atlantis™ Web Order system.
- Rebuilt the core state machine and UI layer — significantly reduced the codebase, eliminated a class of recurring bugs, and cut development time for similar applications by ~20%.
- Built 3D rendering features and extracted reusable libraries from internal tools. Advocated for functional programming techniques that were adopted by other teams.
People Manager / Software Project Manager · Feb 2011 – Apr 2015
Managed distributed teams of up to 12 engineers and analysts. Delivered 16 projects in 4 years — full lifecycle from requirements through deployment and support.
Introduced lean and agile practices. Made a point of doing every team role myself (SE, QA, BA) — hard to manage work you don't understand.
Materialise Dental · Kyiv · Sep 2009 – Feb 2011
Rewrote a core design module nearly from scratch as part of a 2-engineer, 1-QA team. Aggressive schedule, shipped on time, debuted successfully at IDS (largest European dental show). Several design ideas were later adopted by competing products.
First to introduce Continuous Integration and nightly builds in the department. Drove the migration from Subversion to Mercurial.
Earlier roles
- CommerceLab (Kyiv, 2008–2009) — led 3 engineers building Windows security tools. Built an in-house VirusTotal clone and a shared component library.
- IMU (Kyiv, 2006–2008) — Windows security and system maintenance tools, including a local transparent proxy. Designed reusable module architecture.
- Corporate Programs (Kyiv, 2004–2006) — system and network administrator.
Side Projects
Personal needs I solve by building things — and an excuse to experiment with new tech:
- Roude Léiw — Luxembourgish language learning app. Identified a gap, built the product end-to-end.
- LetzCalc — Luxembourg tax calculator. Scratched my own itch, turned out others had it too.
- Trello MCP — MCP server for Trello on Cloudflare Workers. Quick spike to connect AI agents to project boards.
- Gmail Invoice Importer — automates invoice extraction from Gmail. Built to save myself 30 minutes/month.
Education
Taras Shevchenko National University of Kyiv
Master's degree, Mathematics & Software Engineering · 2002 – 2007
Skills
Primary: React, TypeScript, Java, Node.js, AWS. Also shipped production code in C++, C#, F#, Python, Scala, Clojure. Micro frontends, Module Federation, 3D graphics (DirectX/SlimDX).
Languages
- Ukrainian — Native
- English — Full professional proficiency
- Italian — Elementary
- French — Basic
- Luxembourgish — Basic