Олексiй

OLEKSII PROFILE
CHEPURNIAK C#/.NET Backend Developer with 2 years of practical backend development. Focused on ASP.NET Core Web API, clean layered
architecture, EF Core, PostgreSQL, authentication, validation, structured logging and API design.
C#/.NET BACKEND DEVELOPER
I build backend systems using OOP, SOLID, DRY and KISS principles, keep a consistent project structure, and separate
responsibilities between API, Application, Domain and Infrastructure layers. My main practical experience comes from a team
CONTACT Cafe/RRO API project where I own the whole C# backend part, a freelance Python/FastAPI Telegram bot project, and an academic
C++ course project.
[відкрити контакти](див. вище в блоці «контактна інформація») Additional technical background includes Linux administration practice on Arch/Kali, Docker, Nginx, Bash, API testing with
[відкрити контакти](див. вище в блоці «контактна інформація») Swagger/Postman/curl, and cybersecurity tooling such as Nmap, Wireshark, Metasploit, Burp Suite and WPScan.
Telegram: @abooser

WORK EXPERIENCE
GitHub: github.com/4booser
LinkedIn: 773536394
Kyiv, Ukraine
Cafe / RRO Management API Jan 2026 - Present
C# Backend Developer / Architect - team project, in progress
EDUCATION C#, ASP.NET Core .NET 9, EF Core, PostgreSQL, MediatR, JWT, BCrypt, Serilog, Swagger/OpenAPI, Twilio, Npgsql
· Own the entire C# backend part in a 2-person project: API architecture, domain model, persistence layer, authentication and backend structure.
Designed a layered Clean Architecture style backend for cafe/company management: registration/login, company data, venues, staff, roles,
Kyiv Professional College of Maritime and
·
permissions, menus, orders, shifts, warehouses and tech cards.
River Fleet and Transport Technologies of
Implemented JWT Bearer authentication with claims, access/refresh token flow, BCrypt password hashing, roles/permissions and secured company
National Transport University
·
endpoints.
Specialty 121 - Software Engineering Configured EF Core with Npgsql, migrations, separate DbContexts/connection strings for business data, tokens and logs, plus automatic migration
Group PR-214 | 2024-2026
·
startup.
Completed 2 academic years · Used MediatR handlers, repository interfaces, validation, global exception middleware, Serilog file/console logging and Swagger/OpenAPI for
Full secondary education completed testing/documentation.
Applying to National Transport University · Tested endpoints through Swagger, Postman and curl; follows OOP, SOLID, DRY and KISS while keeping one consistent architecture across the
project.
Modeled real business entities and relationships for cafe operations, including company ownership, venue management, staff structure, menus,
TECH EXPERIENCE
·
orders, warehouses, ingredients and technical cards.
· Built backend flow around DTOs, MediatR commands/handlers, repository abstractions, validation, conflict handling and structured API responses.
C# - 2+ years · Configured application startup with dependency injection, JWT authentication/authorization, EF Core migrations, Swagger and Serilog logging.
ASP.NET Core - 1.5+ years
C++ - 1.5+ years
PostgreSQL - 1+ year
CodeHive Jun 2025 - Dec 2025
SQLite - 6+ months Junior C# / ASP.NET Core Backend Developer
Python - 6+ months CodeHive Software - https://codehive.software/
· Worked as a Junior C# / ASP.NET Core Backend Developer, focusing on backend features, API endpoints, validation, data
access and bug fixing.
SKILLS · Used C#, ASP.NET Core Web API, EF Core, SQL/PostgreSQL, Git, debugging tools and existing-codebase workflow in
Languages: C#, SQL, Python, C++ basics practical backend tasks.
· Worked with backend code structure, DTOs, service/repository logic, database-related changes, logs, troubleshooting and
documentation.
C#/.NET: .NET 8/9, ASP.NET Core Web API,
Controllers, Minimal API, Middleware, DI,
Options Pattern, appsettings, async/await, Task, PROJECT EXPERIENCE
CancellationToken, LINQ, Records, Interfaces,
Classes CoursesSalesBot May 2026 - Jun 2026
Freelance Python Backend / Telegram Bot project - stable MVP
Backend: REST APIs, JWT auth, Python, FastAPI, aiogram, PostgreSQL, Redis, SQLAlchemy/Alembic, Docker Compose, pytest/httpx
access/refresh tokens, rate limiting, API key · Built a freelance MVP for selling access to video courses through Telegram: the website/backend creates one-time tokens, the bot activates them and
auth, Swagger/OpenAPI, Serilog, global grants course access.
exception handling, validation, DTOs · Implemented API-key protected FastAPI endpoints for course management, token generation, single/bulk access checks and Redis-based rate
limiting.
Used async PostgreSQL repositories, Alembic schema migrations, Dockerized bot/API/PostgreSQL/Redis services and clean service/repository
Architecture: OOP, SOLID, DRY, KISS,
·
separation.
Clean/Layered Architecture, Repository and · Implemented Telegram bot command flow with /start token activation, user access checks, course list logic and admin-only token creation flow.
Service patterns, CQRS/MediatR, Domain · Designed the API contract with Pydantic request/response models, API-key authorization, health endpoint, token preview generation and access-
Entities, Value Objects, Mapping, Separation of check responses.
Concerns · Practiced production-style backend workflow: environment configuration, Docker Compose services, async session lifecycle, database
commits/rollbacks and API tests with pytest/httpx.
Databases: EF Core, Migrations,
DbContext, PostgreSQL, MySQL, SQLite, Redis,
SQL queries, Fluent API, basic
CourseProject - Workload Distribution May 2026 - Jun 2026
joins/indexes/relationships C++20 Course Project - academic project completed
C++20, CMake, nlohmann/json, JSON file storage, STL, layered architecture, CRUD/search/validation
Developed a console system for managing college workload across teachers, groups and disciplines using local JSON storage.
Security: JWT, BCrypt, password hashing,
·
· Structured the code into UI, Service, Repository and Storage layers with reusable OperationResult responses and header/source separation.
roles/permissions, claims, input validation, SQL · Implemented CRUD, search, input validation, relationship checks, safe deletion protection and cross-platform CMake build scripts.
Injection/XSS awareness, OWASP familiarity · Used C++ header/source separation, STL containers, nlohmann/json and reusable result objects to keep the code organized and predictable.
Practiced backend-like architecture in C++: repositories for data access, services for business rules, storage abstraction and validation before
DevOps/Tools: Git, GitHub, GitLab CI/CD,
·
persistence.
Docker, Docker Compose, Linux/Bash, Arch,
Kali, Nginx, SSH, Postman, curl, pgAdmin,
Visual Studio, VS Code, Rider, PyCharm
Linux & Cybersecurity Practice Jun 2025 - Present
Linux / networking / security tooling practice
Arch Linux, Kali Linux, Bash, SSH, Nginx, Docker, Nmap, Wireshark, Metasploit, Havoc, Burp Suite, WPScan
Bots/Python: aiogram, telebot, Discord 6 months of daily Linux practice on Arch and Kali: terminal workflow, package management, services, SSH, Docker, Nginx and troubleshooting.
bots, FastAPI, asyncio, webhooks, polling, bot
·
Practiced authorized security testing workflows: port scanning, HTTP analysis, WordPress security checks, CVE research and reverse shell theory.
commands, inline keyboards, PostgreSQL
·
· Use security background to think about backend validation, authentication, password hashing, roles, claims, input handling and API exposure risks.

Cybersecurity: Nmap, Wireshark, ADDITIONAL TECHNICAL SCOPE
Metasploit, Havoc Framework, Burp Suite, · Backend practice includes DTO design, request validation, appsettings/options configuration, global error responses and structured logging with
WPScan, port scanning, HTTP analysis, CVE Serilog.
research, reverse shell theory · Database practice includes EF Core migrations/DbContext modeling, SQL queries, MySQL/SQLite/PostgreSQL, Redis and familiarity with joins,
indexes and relationships.
OS Experience: 1 year of daily Linux · Bot/backend experience includes async Python, FastAPI, aiogram/telebot, Discord bots, polling/webhooks, commands, buttons and PostgreSQL-
practice: Arch Linux and Kali Linux, Bash, SSH, backed bot flows.
Nginx, Docker troubleshooting
SELECTED BACKEND PRACTICES
API: controllers, DTOs, validation, Swagger/OpenAPI documentation and consistent error responses.
Currently Improving: xUnit/Moq, ·
Auth/data: JWT, claims, roles, BCrypt, EF Core migrations, PostgreSQL/Npgsql, SQLite/MySQL and Redis basics.
integration tests, SQL joins/grouping/subqueries,
·
Workflow: Git/GitHub, Docker Compose, Linux/Bash, Nginx, Postman, curl, pgAdmin, Visual Studio and Rider.
indexes, DB relationships, OWASP Top 10,
·
CURRENT LEARNING FOCUS
SQLAlchemy, Redis with Python, CMake/STL
· Unit/integration testing with xUnit, Moq, testable architecture and API test automation.
Deeper SQL: joins, grouping, subqueries, indexes, relationships and transaction handling.
LANGUAGES:
·
· Production backend workflow: Docker, Docker Compose, CI/CD, Nginx reverse proxy and Linux VPS deployment.
Ukrainian: Native · Security-oriented backend design: OWASP Top 10, safe input handling, auth flows, rate limiting and API exposure control.
Russian: Native
English: B1 DEVELOPMENT WORKFLOW
· Break backend features into DTOs, validation rules, MediatR handlers/services, repository methods and database changes.
TARGET ROLE · Debug API behavior through Serilog logs, Swagger responses, Postman/curl requests, exception traces and database checks.
Junior / Trainee C#/.NET Backend Developer · Keep code test-ready with interfaces, separated services, predictable error responses and clear validation paths.
Backend Internship · Use Git/GitHub workflow with small commits, readable history, review-ready changes and documented technical decisions.
Remote / Kyiv / Hybrid
PROJECT LINKS
· Cafe/RRO API: https://github.com/4booser/Cafe
WORK STYLE · CoursesSalesBot: https://github.com/4booser/CoursesSalesBot
Backend ownership · CourseProject: https://github.com/4booser/CourseProject
Consistent architecture
Debugging and troubleshooting READY FOR
Self-learning · Backend tasks: API endpoints, authentication, validation, EF Core models/migrations and bug fixing.
Technical documentation · Existing-codebase work: reading logs, reproducing issues, checking database state, refactoring and documentation.