
Serhii O.
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Portfolio
Work experience
Software Engineer (Outsourcing)
b • Self-employed
Sep 2023 - Dec 2025 • 2 yrs 3 mos
Working as a Software Engineer at an outsourcing company, independently delivering full-cycle web applications. Developed a Laravel-based platform with complex Stripe payment integrations, real-time video chat functionality, and a scalable Redis and PostgreSQL backend. Also delivered a separate web application for public transport payments, focusing on reliable transactions, API integrations, and production stability.
Backend Developer (Symfony)
Confidentials • Full-time
May 2022 - Sep 2023 • 1 yr 4 mos
Worked as a Backend Developer on Symfony-based systems ranging from legacy Symfony 3.4 applications to modern Symfony 5.4 services. Integrated the platform with the Ukrainian government Diia service, ensuring secure and reliable data exchange while working within legacy constraints. Led extensive refactoring and modernization efforts to improve system performance, security, and maintainability, including the design and implementation of a secure two-factor authentication system. In parallel, developed a new backend service from scratch using Symfony 5.4, reimplementing and migrating core business logic from an existing Yii2 system. Ensured functional parity with the legacy solution while improving architecture and scalability. Gained hands-on experience with MongoDB and worked with complex data models to support system migration and long-term stability.