Sergei Udalov

Senior Backend Engineer · Ruby on Rails · Real-Time & High-Volume Systems

sergei.udalov@gmail.com · @SergeiUdalov (Telegram) · +7 916 627-26-58 · LinkedIn · GitHub · Remote · CET/CEST timezone

Summary

Senior backend software engineer with 20+ years building high-volume, highly available systems and consumer-facing products across e-commerce, fintech and nation-scale infrastructure. Core stack: Ruby on Rails, PostgreSQL, ClickHouse, Kafka, Redis, Kubernetes — plus production Go and real-time/event-driven design (Kafka → WebSocket). I own projects end-to-end, with measurable outcomes: a 10x data-pipeline speedup, real-time state feeds, and reliable third-party integrations. Now building applied AI/LLM expertise — a fit for a company using AI across the business.

Skills

Languages:Ruby, Go, SQL, JavaScript, PHP, Kotlin, Java
Frameworks:Ruby on Rails, Sinatra, Hanami, GraphQL, RSpec, Sidekiq
Data & Pipelines:PostgreSQL, ClickHouse, Redis, Apache Kafka, RabbitMQ, high-volume data processing
Real-Time & Event-Driven:WebSockets, event streaming, RPC, real-time state feeds
Integrations:third-party APIs, API Hub, payment gateways (QIWI, PayPal, PerfectMoney)
Reliability & Infra:Docker, Kubernetes, GitLab CI/CD, OpenTelemetry, Jaeger, Prometheus, Grafana
Architecture:Microservices, Domain-Driven Design, C4, Event Streaming, UML

Experience

Lead Backend Engineer · Dixy
Nov 2025 — Present

Backend for the Dixy mobile app: high-volume data pipelines, integrations, reliability.

  • Improved inventory synchronization 10x (20 min → 2 min) — a high-volume data pipeline — via ClickHouse→PostgreSQL migration, batch API-Hub integrations, and parallel incremental processing.
  • Built backend powering a consumer mobile app; own cross-cutting changes end-to-end from requirements to production.
  • Built an adapter layer routing notifications across Telegram, Mattermost and other channels.
  • Parallelized GitLab CI pipelines; standardized onboarding (DevContainers) and code-review criteria.
Product Team Lead · Samokat.tech (ecom.tech)
Apr 2023 — Jun 2025

Consumer e-commerce platform; 3 teams, 18+ engineers.

  • Built a Go service streaming Kafka events to WebSocket clients on web and mobile — a real-time state feed across the product.
  • Launched 3 consumer products to production; built the team and processes from scratch.
  • Introduced Domain-Driven Design as the architectural baseline; established technical-debt management.
Technical Lead · Raiffeisen Bank
Jul 2025 — Sep 2025

Banking infrastructure; three cross-functional teams.

  • Established observability across services with OpenTelemetry and Jaeger — key to highly available production.
  • Drove one product's infrastructure migration to 80% completion; unified technical roadmapping.
Senior Developer → Team Lead → Ruby Practice Lead · Balance Platform
Sep 2019 — Apr 2023

Lending-as-a-Service platform: high throughput, analytics, reliability.

  • Increased system throughput and reliability; built a ClickHouse analytics module and business-event collection.
  • Designed an internal RPC protocol and the in-house "Core" framework used across service teams.
  • Led monolith→microservices extraction; optimized core performance and SQL efficiency.
Team Lead · Soft Telematics
Apr 2017 — Aug 2019

Nation-scale toll-road infrastructure (Platon, Oboz, Kospro): real-time data, billing, scale.

  • Built admin interfaces and reporting for the Kospro payment system; extended the Oboz freight-document platform.
  • Enhanced mobile application APIs; implemented automated testing and a reliable test-database pipeline across Platon modules.
Ruby Developer · SeoPult
Mar 2014 — Dec 2015

High-volume data processing for an SEO platform.

  • Worked on a high-load HTTP crawler in Go with RPC access; built a Sidekiq-based worker core with remote RPC and REST API.
  • Sped up JSON/XML/text generation for fast API responses; integrated the QIWI payment system.
Ruby Developer · Source[Lab]
Dec 2015 — Apr 2017
  • Integrated the Idibu CV-advertising API with the Hiring Hub HR service (UK clients); built a document-management system for ORAC.
  • Migrated projects from vendor-locked CI/CD (GitHub, Codeship, Heroku) to open-source GitLab CI and Dokku.
Ruby Developer · Social Quantum
Oct 2012 — Mar 2014
  • Implemented an automated real-time pricing tool — the core of the platform.
  • Reworked the core system's RPC API; built a QIWI payment gateway and financial report generators.
Ruby Developer · Undev.ru
Aug 2011 — Oct 2012
  • Built a payment-acceptance API integrating PayPal, PerfectMoney and other third-party gateways; automated financial reporting.
PHP / Ruby Developer · HROS · High-Web · June Marketing · Sportweek
2006 — 2011
  • PHP/Symfony: online hotel-booking systems (HROS, High-Web). Ruby/Rails: 10+ consumer e-commerce sites and an in-house CMS (June Marketing); sports news portal with live broadcasts (Sportweek).

Education

Moscow Aviation Institute (National Research University)
2008

Specialist degree in Applied Mathematics and Physics (comparable to Master's). Mathematician, Systems Programmer.