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Hacı Şimşek

Hacı Şimşek. Software engineer building backend and distributed systems for high-traffic environments.

5+ years of experience · Software Development Senior Specialist at Sisal · Istanbul

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An order saga

A saga keeps an order consistent across services without one big transaction. Each service commits its own step; when one fails, the steps before it are undone by compensating actions.

  1. Order service

    Create order

    Done

  2. Inventory

    Reserve stock

    Done

  3. Payment

    Charge card

    Done

  4. Shipping

    Book courier

    Done

See it in code

Backend engineer for systems that have to stay up

Software engineer with 5+ years of experience building backend and full-stack solutions across regulated, high-traffic environments. Strong in Java, Spring Boot, distributed systems, CI/CD, and cloud-native delivery, with additional frontend experience in React and Next.js.

At Sisal I have worked on end-to-end development for an international audience, first on the lottery and terminals platform and now on authentication and account services for AreaPrivata, Sisal’s customer account area.

I graduated from Bahçeşehir University on a full scholarship, with a major in Electrical and Electronics Engineering and a minor in Software Engineering, and I share what I learn about architecture patterns through technical articles.

  • Java & Spring Boot
  • Distributed systems
  • CI/CD and observability
  • Cloud-native architecture
Hacı Şimşek
All projects

  1. E-commerce microservices

    Flagship

    Order, inventory, payment and shipping services kept consistent by an event-driven saga over Kafka: a failed payment releases the stock, a failed shipment refunds and releases it.

    Java

  2. NotifyHub

    Reminders fire through Kafka, delivery runs on RabbitMQ with retries and a dead-letter queue, and a React dashboard tracks every attempt.

    Java

  3. Strangler fig pattern

    A legacy Spring Boot monolith moved to new code step by step, with old and new paths running side by side.

    Java

  4. Circuit breaker pattern

    A hand-written circuit breaker between an order and an inventory service.

    Java

Where I've worked

Most of my recent work sits in backend-heavy systems where scale, release confidence, observability, and service reliability matter as much as implementation itself.

  1. Sisal

    Jun 2022 – Present

    Promoted

    Software Development Senior Specialist

    Jan 2025 – Present · AreaPrivata · Backend and platform engineering

    Building Spring Boot microservices and production-ready backend flows in a regulated digital gaming and payments environment.

    • Build backend microservices for AreaPrivata, Sisal’s customer account area, with Java 11, Spring Boot and Maven, across authentication, account, session, profile and content domains.
    • Designed and optimized core services for registration, profile management and gateway communication.
    • Built resilient integrations with asynchronous messaging over RabbitMQ, retry strategies and caching with Redis Sentinel.
    • Led the migration of the infrastructure to a new API-driven model, defining standards and best practices for consistency across services.
    • Work with DevOps on deployment and monitoring with Kubernetes and ArgoCD, plus observability, load testing and performance tuning.

    Software Engineer

    Jun 2022 – Jan 2025 · Lottery and Terminals · Full-stack and authentication

    Built authentication infrastructure and end-to-end applications for the lottery and gaming platform.

    What I did · Software Engineer
    • Designed and implemented the Orion module, a new authentication infrastructure integrated with the full-stack application, using React.js, Java and OSGi (a modular Java platform) for scalability, security and compatibility.
    • Member of the Lottery and Terminals team, developing applications end to end with React.js and OSGi.
    • Collaborated on global projects, joining international meetings and business trips that fed into strategic decisions.

  2. Nuevo Software House

    Sep 2021 – Jun 2022

    Software Engineer

    Enterprise web applications

    Delivered end-to-end web applications for enterprise clients such as Türk Petrol, AvivaSA, Kordsa and Tavuk Dünyası.

    What I did · Software Engineer
    • Built business-facing applications with React.js and SharePoint for clients including Türk Petrol, AvivaSA, Kordsa and Tavuk Dünyası.
    • Balanced maintainability, user experience and client-specific workflows across enterprise implementations.
    • Supported the design, implementation and release of tailored solutions with product and delivery teams.

  3. Telenity

    Jun 2021 – Aug 2021

    Software Engineer Intern

    Telecom backend

    Internship

    Started in telecom-focused backend development and messaging systems.

    What I did · Software Engineer Intern
    • Contributed to VAS and messaging features with Java and Spring Boot.
    • Supported the company's work on 5G technologies.
    • Learned how scalable backend services behave in a demanding telecommunications environment.

  4. Bahçeşehir University AI Society

    Sep 2019 – Jun 2020

    Project Manager

    Community and events

    Leadership

    Organized AI-focused seminars, workshops and networking events for students and professionals.

    What I did · Project Manager
    • Promoted artificial intelligence through educational initiatives that raised engagement in the academic community.
    • Coordinated projects and events in a team-oriented environment.

Tools I use to ship and run systems

The stack behind the roles above, from service code and messaging to delivery pipelines and the architecture patterns I write about.

Languages
  • Java
  • JavaScript
Backend
  • Spring Boot
  • Maven
  • OSGi
  • REST APIs
Messaging and data
  • RabbitMQ
  • Kafka
  • Redis
  • PostgreSQL
  • MySQL
Cloud and delivery
  • Kubernetes
  • ArgoCD
  • Docker
  • CI/CD
Observability
  • Grafana
  • Prometheus
  • Load testing
Frontend
  • React
  • Next.js
  • SharePoint
Architecture
  • Microservices
  • Saga pattern
  • Circuit breaker
  • Backend for frontend
  • Clean architecture

Engineering foundation across hardware and software

My background combines software systems thinking with electrical and electronics fundamentals, which still influences how I reason about architecture, constraints, and reliability.

  1. Sep 2017 – Jun 2021

    Major

    BSc, Electrical and Electronics Engineering

    Bahçeşehir University · Istanbul, Turkey

    Full scholarship

  2. Sep 2019 – Jun 2021

    Minor

    BSc, Software Engineering

    Bahçeşehir University · Istanbul, Turkey

Latest writing

All articles

  1. What is the Saga Pattern?

  2. Strangler Fig Pattern

  3. Centralized Service Registry