Available for new projects · Istanbul & remote

Nihat Çelik — Senior Software Engineer & Technical Lead

For 7+ years I've been designing scalable backend systems and microservices architectures in the .NET ecosystem. From enterprise ERP platforms to logistics, from SAP integrations to e-commerce marketplaces — I've built the systems where the load actually lands, and led the teams that built them.

  • 7+ years of professional experience
  • 8 engineers led at peak
  • 30%+ API response time improvement
  • 0→30% test coverage increase

Services

Backend & microservices architecture

Moving from a monolith to service-based architecture, drawing domain boundaries, inter-service messaging. I use CQRS and Clean Architecture not to follow the book, but so the team can make changes with confidence.

  • .NET 8
  • CQRS
  • MediatR
  • RabbitMQ
  • Clean Architecture

Legacy modernization

Making systems that work — but nobody dares touch — safe to move, without stopping production. I ran the .NET 8 migration at Sendeo and the legacy → CQRS transition at Amaris. Technical debt isn't a slide in a deck; it's work that goes into the sprint.

  • .NET Framework → .NET 8
  • Strangler Fig
  • Refactoring
  • Tech debt management

Enterprise system integrations

I built the SAP and ADIS (MobilPark) integrations at Koton, and the Trendyol / N11 / Hepsiburada marketplace integrations at Sendeo. In enterprise integration the real work isn't the code — it's the failure and reconciliation scenarios.

  • SAP
  • ADIS / MobilPark
  • Marketplace APIs
  • e-Invoicing
  • ERP

Performance & observability

At Sendeo I cut API response times by over 30% through caching strategies and code optimization; at Extratik we brought them under 500 ms. Measurement infrastructure first, optimization second — the reverse is guesswork.

  • Redis
  • OpenTelemetry
  • ELK / Kibana
  • AppOptics
  • SonarQube

Technical leadership & consulting

I've led cross-functional teams of up to 8. Architecture review, establishing PR and code review processes, development standards, sprint planning and technical roadmaps — what speeds a team up is process, not pressure.

  • Architecture review
  • Code review culture
  • Mentorship
  • CI/CD
  • Sprint planning

ERP & business process automation

At Tatko I define the architecture of the ERP platform; at Extratik I designed a BPM system that automated internal workflows. Plus 2.5 years of domain depth in pre-accounting and e-invoicing from SahaTek.

  • ERP modules
  • BPM
  • Hangfire
  • Quartz
  • Process automation

Experience

From 2019 to today

Across logistics, retail, ERP and fintech-adjacent pre-accounting — from developer to technical lead.

  1. — Present

    Technical Lead · Tatko Lastik

    Istanbul, Türkiye

    Technical guidance and mentorship for a team of 5. I define the system architecture of the company's ERP platform and make the key technical decisions. Production deployment planning, refactoring initiatives, establishing team standards and workflows, sprint planning and technical roadmap.

  2. —

    Senior Software Developer · Koton

    Istanbul, Türkiye

    Led development of key enterprise modules including HR systems and internal business applications. Delivered SAP and ADIS (MobilPark) integrations, improving data consistency and reducing manual operations. Designed microservices-based architectures and built responsive web applications with React.

    • SAP
    • Microservices
    • React
    • .NET
  3. —

    Software Lead · Extratik

    Istanbul, Türkiye

    Led a cross-functional team of 4 (backend, frontend, QA). Designed and developed a BPM system to automate internal workflows. Led cross-platform mobile development with Flutter. Reduced API response times to under 500 ms and containerized applications with Docker.

    • BPM
    • Flutter
    • Docker
    • <500ms API
  4. —

    Software Lead · Koç Holding — Sendeo

    Istanbul, Türkiye

    Led an 8-person engineering team (backend, frontend, QA). Reduced API response times by over 30% through caching strategies and code optimization. Migrated background job processing to a RabbitMQ-based architecture and upgraded systems to .NET 8. Prioritized technical debt and folded it into sprint planning.

    • .NET 8
    • RabbitMQ
    • Redis
    • CQRS
    • MediatR
    • Kibana
    • Quartz
    • NUnit
  5. —

    Senior Software Developer · Koç Holding — Sendeo

    Istanbul, Türkiye

    Developed logistics applications and courier integrations. Applied SOLID principles and raised code quality through unit testing with NUnit.

    • .NET 6
    • OpenTelemetry
    • CQRS
    • NUnit
    • MsSQL
  6. —

    Backend Developer Consultant · Sendeo (via Amaris Consulting)

    Istanbul, Türkiye

    Integrated major e-commerce platforms including Trendyol, N11 and Hepsiburada. Migrated legacy systems to CQRS architecture. Increased unit test coverage from 0% to 30%.

    • Trendyol
    • N11
    • Hepsiburada
    • CQRS
    • Coverage 0→30%
  7. —

    Software Developer · SahaTek

    Istanbul, Türkiye

    Developed pre-accounting and e-invoice modules. Optimized reporting and asynchronous tasks.

    • e-Invoicing
    • Pre-accounting
    • Reporting
  8. —

    Software Intern (Erasmus+) · Teknoza

    Antwerp, Belgium

    Developed mobile prototypes using React Native.

Education

B.Sc. in Software Engineering

Firat University, Elazig · 2019

Certificate

Secure Web Application Development

Deloitte Academy · 2023

Awards

1st place, Algorithm Contest

Firat University · 2017  ·  1st place, IT Contest · 2014

Stack

The tools I work with daily

Everything on this list is something I've run in production and can stand behind — not names added to pad a CV.

Core

  • C#
  • .NET 8
  • .NET Core
  • .NET Framework
  • RESTful APIs
  • Microservices

Architecture

  • CQRS
  • Clean Architecture
  • Onion Architecture
  • SOLID
  • MediatR

Frontend

  • React
  • Flutter
  • React Native

Cloud & DevOps

  • Azure DevOps
  • GitHub Actions
  • CI/CD
  • Docker
  • Kubernetes

Data

  • MS SQL Server
  • PostgreSQL
  • MySQL
  • Redis

Messaging & Jobs

  • RabbitMQ
  • Hangfire
  • Quartz

Observability

  • OpenTelemetry
  • ELK Stack
  • Kibana
  • AppOptics

Tools

  • Git
  • GitHub
  • Bitbucket
  • Jira
  • SonarQube
  • NUnit

How I work

How a project runs with me

I don't like surprises. At every stage you'll know where we are and what the next step is.

  1. Discovery

    I get to know the existing system, the constraints and the actual business goal. More often than not, the problem stated isn't the problem that needs solving.

  2. Architecture & plan

    I lay out the alternatives, their costs and their consequences, and I make a recommendation. You make the call — but not blindly.

  3. Delivery

    Small, reviewable increments shipped regularly through CI/CD, with working software at every step. No "I'll show you at the end."

  4. Handover

    Documentation, the reasoning behind architectural decisions, and mentorship for the team. The system has to stay touchable after I'm gone.

Contact

Let's talk about your project

Got a new system to build, a legacy application that needs migrating, or an architectural decision you'd like a second opinion on? A short call usually gets further than weeks of discussion. First call is free.

Istanbul, Türkiye Open to remote work Turkish / English (B2)

Or write directly

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