# Sergei Udalov **Staff Backend Engineer | Distributed Systems | Ruby/Rails** [sergei.udalov@gmail.com](mailto:sergei.udalov@gmail.com) | [@SergeiUdalov](https://t.me/SergeiUdalov) | [+7 916 627-26-58](tel:+79166272658) | [LinkedIn](https://www.linkedin.com/in/sergeiudalov/) | [GitHub](https://github.com/sergio-fry) | Remote | EU Time Zone ## Summary Staff-level Backend Engineer with 15+ years of experience building high-load and distributed systems, primarily with Ruby/Rails. Hands-on engineer focused on system architecture, scalability and reliability, with deep experience in PostgreSQL, Kafka, ClickHouse and Kubernetes. Led architecture and delivery across e-commerce, fintech and consumer platforms, from modernizing legacy systems to launching new products from scratch. Experienced in DDD, event-driven architecture, observability and engineering productivity. Practical experience applying AI/LLM: delivered production solutions built on LLMs and agentic approaches, including a voice bot and a code-review agent. Independently developing agentic engineering and applying AI agents in my own engineering projects. ## Skills - **Languages & Backend:** Ruby, Ruby on Rails, PostgreSQL, Kafka, Redis, ClickHouse, Go - **Architecture:** Distributed Systems, Event-Driven Architecture, Microservices, DDD, API Design, Legacy Modernization - **Infrastructure & Observability:** Kubernetes, Docker, AWS, GitLab CI/CD, OpenTelemetry, Prometheus, Grafana - **AI/LLM:** LLM orchestration, AI agents, LangChain ## Experience ### Lead Backend Engineer - Dixy *Nov 2025 - Present* Core backend for the Dixy mobile app: integrations, APIs, performance and delivery. - Improved inventory synchronization 10x (20 min -> 2 min) via ClickHouse->PostgreSQL migration, batch API-Hub integrations, and parallel incremental processing. - Owned full-cycle delivery of cross-cutting backend changes (requirements -> production) for a high-traffic mobile inventory and integration system serving 2,000 stores (~1,000 RPS, 800 GB+ data). - Parallelized GitLab CI pipelines, cutting pipeline wait time from ~30 min to ~5 min for two engineering teams. ### Technical Lead - Raiffeisen Bank *Jul 2025 - Sep 2025* Banking infrastructure; technical leadership across three cross-functional teams. - Led architecture and delivery of a banking infrastructure migration: rebuilt C4 documentation for ~50 services, introduced distributed tracing across 20 services, and drove the migration to ~80% completion. - Designed and delivered an AI voice bot using LangChain and LLM orchestration, automating ~7% of routine customer payment inquiries. ### Product Team Lead - Samokat.tech (ecom.tech) *Apr 2023 - Jun 2025* Scalable e-commerce platform (consumer apps); launched products from scratch. - Architected and delivered backend for 3 new consumer products from zero to production (150 RPS, 800K+ users, 20 GB data) - Kafka event streaming, WebSocket real-time layer, DDD boundaries. - Built a Go platform service streaming Kafka events to WebSocket clients across multiple products, handling ~500 concurrent connections and ~50 events/sec. - Built an AI code-review agent (Ruby service on GitLab webhooks) that analyzed changes against project conventions and flagged common security and performance issues. - Established Domain-Driven Design as the architectural standard and a lightweight technical-debt process adopted by multiple product teams. ### Senior Developer -> Team Lead -> Ruby Practice Lead - Balance Platform *Sep 2019 - Apr 2023* Lending-as-a-Service (LaaS) platform: credit automation, internal platform, Ruby standards. - Built in the LaaS credit-automation domain; optimized core performance and SQL efficiency; led monolith->microservices extraction. - Designed an internal RPC protocol and built the in-house "Core" framework adopted by multiple service teams. - Increased system throughput and reliability; built a ClickHouse analytics module and business-event collection for analytics. - Defined code-review standards and a Ruby competency matrix adopted across the engineering organization. ### Team Lead - Soft Telematics *Apr 2017 - Aug 2019* Nation-scale toll-road systems: Platon (truck toll collection), Oboz (freight documents), and Avtodor toll roads. - Built reporting services and mobile APIs for Platon, a nation-scale toll-collection system (1M+ vehicles); implemented automated test pipelines and reliable test-database builds across modules. - Extended the Oboz freight-document platform with document-processing and reporting capabilities for freight carriers. - Built admin interfaces and payment reporting for Avtodor toll-road systems. ### Ruby Developer - Source[Lab] *Dec 2015 - Apr 2017* - Integrated the Idibu CV-advertising API with the Hiring Hub HR service; built a document-management system for ORAC (UK clients). - Migrated projects from vendor-locked CI/CD (GitHub, Codeship, Heroku) to open-source GitLab CI and Dokku. ### Ruby Developer - SeoPult *Mar 2014 - Dec 2015* Backend services and public APIs for an SEO platform. - Built the internal backend core - Sidekiq workers, remote RPC, RESTful API - and sped up JSON/XML/text generation for fast API responses. - Worked on a high-load HTTP crawler in Go with RPC access; integrated the QIWI payment system. ### Ruby Developer - Social Quantum *Oct 2012 - Mar 2014* - Reworked the core system's RPC API; migrated PGQ workers to the new internal API. - Built a QIWI payment gateway via REST and financial report generators. ### Ruby Developer - Undev.ru *Aug 2011 - Oct 2012* - Built a payment-acceptance API integrating PayPal, PerfectMoney and other gateways; automated financial reporting with Google Analytics. ### PHP / Ruby Developer - HROS | High-Web | June Marketing | Sportweek *2006 - 2011* - PHP/Symfony: online hotel-booking systems (HROS, High-Web). Ruby/Rails: 10+ e-commerce sites and in-house CMS (June Marketing); sports news portal with live broadcasts (Sportweek). ## Projects & Publications - **HeavyTech Podcast** - host, covering AI/LLM engineering, system architecture, and backend patterns. - **RubyRussia** 2023/2024/2025 - speaker on architecture, test automation, and database migrations. ## Education **Moscow Aviation Institute (National Research University)** - 2008 Specialist degree in Applied Mathematics and Physics (comparable to Master's). Mathematician, Systems Programmer.