# Furkan Aygül **Computer Engineer | Backend & Systems Engineer** Istanbul, Turkey - Email: contact@furkanaygul.com.tr - Website: https://www.furkanaygul.com.tr - LinkedIn: https://www.linkedin.com/in/aygulfurkan - GitHub: https://github.com/furkanaygul --- ## Profile Computer engineer with deep .NET 8 expertise, specialized in microservice architectures, Domain-Driven Design and large-scale industrial IoT / SCADA systems. I have led — end-to-end and largely solo — the architecture, implementation and operational rollout of enterprise ERP platforms, multi-protocol industrial data acquisition services and real-time SCADA dashboards. My toolbox spans backend performance work (concurrency, lock-free data structures, dirty-set patterns), DevOps (Docker, GitHub Actions, self-hosted runners) and full-stack systems / networking (OpenVPN, Postfix mail server, Linux server hardening). --- ## Core Skills **Languages & Frameworks:** C#, .NET 8 Web API, ASP.NET Core, Entity Framework Core, NPoco, JavaScript, TypeScript, React (Ant Design, React Query), PHP, Dart / Flutter, Node.js / Express, Python (basic). **Architecture & Patterns:** Microservices, Domain-Driven Design (DDD), Clean / Layered Architecture, CQRS, Plugin Architecture, Event-Driven, RESTful API, JWT / OAuth, Rate Limiting. **Concurrency & Performance:** Hosted Services, IHostedService + IProtocolRuntime decomposition, ConcurrentDictionary, SemaphoreSlim budgets, System.Threading.Channels (bounded worker pool), dirty-set pattern, lock-free caches, EF Core UNION ALL view-based hot-path optimization. **Databases:** PostgreSQL, MSSQL, MongoDB (time-series), Redis (StackExchange.Redis), EF Core migration / seed pipelines, hash-tracked SQL artifact migration. **Messaging & Real-Time:** SignalR, MQTT (MQTTnet), TCP Listener, WebSockets. **Industrial Protocols:** Modbus TCP, Modbus RTU, Profinet, Profibus, MQTT, UART, BLE. **DevOps & Ops:** Docker, Docker Compose, Nginx, YARP Reverse Proxy, GitHub Actions (self-hosted runner), Linux system administration, OpenVPN, Postfix mail server (SPF/DKIM/DMARC/PTR), firewall, port forwarding, dynamic IP blocking. **Testing & Quality:** xUnit (round-trip + tamper detection), CI anti-pattern lint, warning regression guard, baseline-based quality gates. **Observability:** Serilog, Seq, PostgreSQL log sink. **Security:** AES-256-GCM credential encryption, JWT + hashed refresh token rotation, role/permission-based authorization, forwarded headers, security headers. **Other:** OpenXML, Puppeteer, ExcelJS, ElectronJS, Chrome Extension, ESP32 / Arduino, BLE, Smartsheet integration. --- ## Professional Experience ### Backend & Systems Engineer — UESTCO Enerji Sistemleri **Nov 2021 – Present · Maltepe, Istanbul** _(Started as a Full Stack Developer; the role evolved over time toward backend architecture, industrial IoT and platform operations.)_ - Built enterprise-grade web applications and RESTful APIs on .NET Core / .NET 8 using microservice and API Gateway patterns. - Designed and shipped a DDD-based ERP platform (UESTCO ERP) split into Identity and CRM bounded contexts; implemented JWT + refresh token, ASP.NET Core Identity, role/permission, Redis cache and a full sales analytics suite. - Architected and implemented a plug-in protocol industrial IoT acquisition service (Nexa-Flow) supporting Modbus TCP, Modbus RTU, MQTT, TCP Listener and Virtual devices over a single shared read pipeline; ran two major refactors (DI cleanup + performance) introducing dirty-set patterns, ConcurrentDictionary hot-path lookups and a channel-based bounded fire-and-forget worker pool. - Built CI/CD pipelines on Docker, GitHub Actions and self-hosted runners; added quality gates such as anti-pattern lint and compiler-warning regression guards. - Ran Linux and Windows server operations: VPN, FTP, SFTP, SSH, mail server (Postfix + SPF/DKIM/DMARC/PTR) and network security (OpenVPN, firewall, segmentation). - Implemented industrial protocols (Modbus, Profinet, MQTT) for SCADA / automation projects and powered real-time dashboards and alarms via SignalR. - Set up test automation pipelines using xUnit, Selenium and API testing tools. - Optimized database performance on PostgreSQL, MSSQL and MongoDB (indexes, views, UNION ALL, time-series collections, partial unique indexes). --- ## Selected Projects ### Nexa-Flow — Plug-in Protocol Industrial IoT Acquisition Service *.NET 8 · PostgreSQL · MongoDB time-series · SignalR · MQTTnet · NModbus · NCalc · Channels · Docker · xUnit* Designed a plug-in protocol architecture in which five protocols (Modbus TCP, Modbus RTU, MQTT, TCP Listener, Virtual) converge into a single protocol-agnostic `DeviceReadPipeline(List)` contract. Adding a new protocol requires no changes to cache, alarm, calculation or SignalR fan-out code. **Technical Highlights** - **Performance refactor:** GUID-prefix substring scans → ConcurrentDictionary O(1) lookups; full-table scans → dirty-set pattern + UNION ALL active views (`vw_active_tags`, `vw_active_enabled_tags`, `vw_active_devices`); unbounded `Task.Run` → channel-based bounded fire-and-forget worker pool; `SemaphoreSlim(64)` global read budget against thread-pool starvation. - **Hash-tracked SQL migrator:** Startup migrator that loads `Migrations/Sql/*.sql` as embedded resources and tracks each by SHA-256, re-applying on change — eliminating manual `psql -f` deployment steps. - **Security:** AES-256-GCM for broker / export credentials, JWT with DB-hashed refresh token rotation, production fail-fast on missing identity seeds or export keys. - **Operations:** Split `/health` (liveness) and `/ready` (readiness, Postgres `SELECT 1` + Mongo admin ping + service init), 15-retry DB startup barrier, HA-friendly migration flag, Docker Compose multi-service deployment (Postgres, Mongo, Seq, app), non-root container. - **CI / Quality:** `tools/check-antipatterns.ps1` (blocks new `GetList().Where(...)`, unbounded `Task.Run`, full-scan patterns via grandfathered baselines) and `tools/check-warnings.ps1` (compiler warning regression guard). ### UESTCO ERP — DDD-Based Microservice ERP Platform *.NET 8 · ASP.NET Core Identity · PostgreSQL · Redis · YARP · Docker · Serilog + Seq · GitHub Actions* Positioned Identity and CRM as independent bounded contexts. Identity ships users, roles, endpoint-level permissions, JWT + hashed refresh tokens, rate-limited login/refresh endpoints and a Redis-backed permission cache with startup warmup. CRM covers customers, contacts, addresses, products, customer-specific discounts, projects, quotations, multi-step quote approval workflow, OpenXML / Puppeteer document generation (offer / proforma / order), lookup translations, global search, column visibility config and a full sales analytics suite (dashboard, funnel, timeline, segmentation by sector / product / customer / user). A YARP-based API Gateway provides a single entry point with centralized CORS, security headers and forwarded-header handling. Backed by per-service PostgreSQL, Docker Compose orchestration, Serilog + PostgreSQL log sink + Seq for observability and a self-hosted GitHub Actions staging deployment pipeline. ### IPACK SCADA Systems — Industrial Monitoring & Data Processing Platform Modernized a legacy PHP/MSSQL SCADA stack, added C# Windows Forms data acquisition modules, built a TCP Server with direct Modbus communication, and implemented dynamic IP-blocking security automation. ### SCADA Dashboard Drag-and-drop, widget-based real-time station-automation dashboard built on ASP.NET Core, PostgreSQL, SignalR and modern JavaScript. ### Detector Monitoring System Cross-platform desktop app built with ElectronJS + Node.js + ModbusRTU; trend graphs, tabular reports and config-driven customization without an admin panel. ### Tube Filling Tracking System Cross-platform Flutter mobile app using BLE to read tube measurement data from device cards, with on-device mathematical processing and visualization. ### UART-BLE Gateway ESP32 firmware bridging UART-based tube-occupancy sensors to BLE, enabling control and monitoring from any Bluetooth-capable client — a lightweight, low-latency industrial IoT gateway. ### Mail Server Enterprise Postfix deployment with SSL/TLS and Postfix Admin UI; SPF, DKIM, DMARC and PTR records configured for top-tier deliverability and 9/10+ spam/security ratings. ### Enterprise Network & Servers OpenVPN-based remote access, multi-VLAN segmentation, firewall and port-forwarding policies, plus full lifecycle operations on physical servers (installation, OS hardening, patching, backup). ### Other Projects Chrome Extension – NAS automation · Mail Signature Generator · Warehouse Entry/Exit (Flutter + QR + Google Sheets API) · SMS Sender (field-data alerts for internet-less SCADA sites) · Station Automation (C# + PostgreSQL + Modbus). --- ## Education **Düzce University** — B.Sc. in Computer Engineering Graduated: 2021 · GPA: 2.96 --- ## Certifications - **Agile Project Management Training Certificate** — ISO Akademi & AI EDIH TR · 12 December 2025 - **From Idea to MVP: Accelerated Project-Based Innovation Bootcamp** — The School of Technology & Innovation · 7 December 2025 - **C1 Level English Certificate** — American Culture Language School · 10 April 2025 --- ## Languages - Turkish — Native - English — C1 (Academic / Professional) --- ## Personal - Born in Balıkesir, Turkey - Based in Istanbul - Age: 27