Oleksandr Sierov
Backend Software Engineer (C# / .NET, Azure) | Payments, billing & e-invoicing SaaS | MSc AI Engineering
About Me
Backend-focused software engineer with 5+ years building cloud-native SaaS ERP, accounting and invoicing platforms in C#, .NET, ASP.NET Core, SQL Server and Microsoft Azure at Cegid Primavera and Shine. I designed a .NET 9 payments microservice integrating Stripe, migrated four legacy .NET Framework products to modern .NET, and rebuilt the SAF-T import pipeline, cutting related support tickets by about 70%. I take work end to end, from architecture and prototypes to release management across four product teams, and I mentor and onboard other engineers. I am also pursuing an MSc in Artificial Intelligence Engineering at ISEP, applying LLMs, multi-agent systems and machine learning (Python, PyTorch) to real business problems. My thesis explores LLM-assisted root cause analysis of performance degradations in a production SaaS invoicing application. EU citizen, open to remote roles or relocation.
Work Experience
Shine
- Payments: integrated Transpayrent for recurring subscription payments of the product.
- Frontend modernization: migrated a jQuery version deprecated since 2013 and the legacy DataTables grid to current versions, and built a reusable list component used across multiple modules.
- Implementing regulatory compliance features (e-invoicing, tax reporting) for the Spanish market.
Cegid Primavera
- Payments: designed a .NET 9 microservice integrating Stripe as Payment Service Provider for ContaSimple.
- Modernization: migrated four products (Jasmin, Rose, Valuekeep, People) from .NET Framework 4.7.2 to .NET 6/7/8, and delivered the Framework 14.2 upgrade of Rose and Jasmin.
- Compliance: rebuilt SAF-T import with C# Azure Functions parsing XML files (40-50 per month), which let the legacy importer be decommissioned, removed recurring processing bugs and cut monthly support tickets by about 70%.
- Performance: optimized SQL queries behind requests and dashboards, and list and workflow performance across the products.
- Data migration: built the Rose2Business customer data migration prototype, adopted by the team as the basis of the final solution.
- Security: proposed malware scanning for Azure Storage uploads, leading to the adoption of Microsoft Defender for Storage.
- Ownership: owned release management for Framework Elevation and Rose2Business, coordinating four product teams.
- Team: code reviews, architecture design, mentoring and onboarding of junior engineers, and on-call for production incidents in a 9-12 person team.
Checkmarx
Skills
Languages
Education
Instituto Superior de Engenharia do Porto
Advanced AI: LLMs, multi-agent systems, machine learning, deep learning, computer vision, expert systems and decision support. Thesis: "From Logs to Backlog: Evidence-Grounded, LLM-Assisted Diagnosis of Performance Degradations in a SaaS Invoicing Application".
Key Projects
Multi-Agent Architecture for Autonomous Robotic Perception and Control
Distributed SPADE agents over XMPP coordinating a TIAGo mobile robot through FIPA Contract Net auctions (Vickrey pricing, reputation, Bayesian bidding), with ROS 2 / Nav2 / Webots via MQTT and local LLMs via Ollama.
Autonomous Navigation in Dynamic Environments
YOLO detection and YOLOv11 segmentation with a ResNet18 + LSTM temporal model (COCO, KITTI), plus bilingual PT/EN speech-to-text voice commands with BERT multi-label intent classification and word2vec.
NineGears AI (Robot Anomaly Detection)
Expert system for robot anomaly detection using Fuzzy Logic and Drools (Java/Prolog) integrated with Python.
Car Price Estimation Using Consumer Preferences
Intelligent vehicle price prediction system using LightGBM, XGBoost, Random Forest, and Linear Regression. Implements TOPSIS for multi-criteria decision making.
Instituto Politécnico do Cávado e do Ave
Final grade 16/20. Specialized in full-stack development and distributed ledger technologies. Designed a platform from scratch incorporating Backend, Frontend, and Android components. The Master's Thesis focused on a Blockchain-based evidence management platform for legal compliance.
Key Projects
Evidence Management DApp
Blockchain-based evidence management platform ensuring data integrity and chain of custody for legal environments. Built as a full-stack DApp with a focus on immutability and compliance.
Instituto Politécnico do Cávado e do Ave
Final grade 16/20. Final project: PL/SQL parser for static analysis (Checkmarx). Acquired strong foundations in software engineering, algorithms, and data structures. Developed diverse projects exploring technologies such as C#, C, C++, SQL, MongoDB, React, and Angular.
European Innovation Academy
Intensive entrepreneurship program focusing on innovation and startup development.
Projects
TriggerPoint
Live social and marketplace platform for the airsoft community: Stripe payments, real-time chat, OAuth (Google, Apple), web push, 6 languages, Prometheus / Grafana / Loki observability and GitHub Actions CI/CD.
Spotify2Yt
Cross-platform desktop app (Windows, macOS, Linux) that migrates Spotify liked songs and playlists to YouTube Music with no API keys required.
More on GitHub
Check out my repositories, academic assignments, and open-source contributions on my GitHub profile.