Contributed to building a greenfield microservices payment gateway, replacing a vendor monolithic solution, taking full ownership of core backend services. - Developed core microservices exposing the public REST API of the payment gateway, owning the contract implementation for payment orders and financial operations — MVP delivered in under 6 months - Implemented and maintained BPMN process models in Camunda for orchestrating 3DS card payment flows (frictionless, challenge, SDK), including tokenized cards (Apple Pay, Google Pay), refunds, and reversals across multiple transaction processors — with a dedicated process testing infrastructure to validate business flows in isolation prior to deployment - Built Kotlin-based E2E testing infrastructure with a custom DSL for declarative payment flow testing, covering complex multi-step scenarios with async webhook handling and eventual consistency — enabling developers and QA to write and run tests across multiple environments, with Allure TestOps integration and GitLab CI pipeline - Designed and maintained CI/CD pipelines across microservice builds, automated testing, code quality, and API contract validation - Implemented PCI DSS security controls — sensitive data masking, encryption, and compliant data storage — as shared libraries adopted across multiple microservices - Built a modular k6 performance testing framework for payment gateway flows — smoke, load, and stress tests with real-time Grafana dashboards, improving throughput from <1 TPS to meet SLO of 20 TPS, with peaks validated up to 100 TPS - Contributed to observability across microservices — shared libraries for metrics, tracing, and structured logging, custom traces for performance profiling in Jaeger, and an internal notification service replacing a paid Slack integration

- Developed standalone mode of Axibase Time Series Database with embedded Hbase cluster in local mode - Implemented convenient fluent API client for ASTS protocol of Moscow Exchange financial data, which wrapped native libraries into Java Maven library - Implemented Fractional Differentiation algorithm for time‑series data, which aimed to make time‑series stationary - Developed Axibase Time Series Database schema for different financial data - Implemented a Type‑ahead system for financial instrument suggestions

- Developed different layers of Axibase Time Series Database: schema, filters using underlying HBase database; service layer with Spring(Core, Security, Data, MVC, Testing), front‑end with Freemarker, Javascript, and testing these layers utilizing JUnit, Mockito, Hamcrest - Implemented Singular Spectrum Analysis forecast algorithm in Java using Statistical Machine Intelligence and Learning Engine and wrapped it in the convenient REST API endpoint - Migrated Markdown documentation to websites using Vuepress, Algola, Hugo. Added automated spell‑checks, and checks for compliance with Technical Writing Guide integrated into Continuous Delivery process in GitHub Actions - Performed deployment of Axibase Time Series Database in distributed cluster mode to Azure cloud

- Developed Spring Batch‑based ETL application which transforms metrics from different sources (HTTPS, JSON, JDBC, Kafka, Docker API, AWS Cloudwatch API) into Axibase Time Series Database format - Developed Docker images for Axibase Time Series Database and related projects utilizing Shell, Bash languages - Enhanced development operations by integrating legacy projects into Continuous Integration/Delivery pipelines in Jenkins, Travis CI, and GitHub Actions platforms. - Implemented Grafana integration plugin for Axibase Time Series Database using Typescript/Javascript languages

Developed High Load microservice‑based system using technologies: Spring, EJB, Oracle Database, JDBC Template - Developed client‑side Java desktop multithreading application utilizing Standard Widget Toolkit

- Implemented Java testing framework using TestNG library which allowed to write integration tests for SQL/TCP/REST API of Axibase Time Series Database - Developed API clients utilizing REST endpoints of Axibase Time Series Database for different programming languages (Java, Python, NodeJS) - Implemented demo applications utilizing features of Axibase Time Series Database such SQL, Rule Engine, and Charts configuration syntax - Implemented crawlers and utilities using Java and Bash languages for automation collecting of historical data - Wrote documentation for new features using Markdown markup language

- Developed client‑server application for office map navigation for corporative usage utilizing the following stack: Spring Boot as a backend framework, Post‑ greSQL as database and AngularJS framework with D3.js library on the frontend side - Performed end‑to‑end testing of web pages with Protractor - Enhanced coverage by unit tests of existing AngularJS components operating the following tools: mocha, chai, karma - Developed UI components via migration from Bindows framework to AngularJS