Berkay Hellagün
builds fast, scalable backend systems on .NET.

Mid+ backend engineer focused on complex business processes, performance optimization and simplifying architectures. Asynchronous processing, relational database design and production systems used by large user bases.

$mail mail@berkayhellagun.com

berkay@id3 — zsh

What I do

From design all the way to going live.

Backend architecture. I write REST APIs and services with .NET Core, thinking about performance from day one.
Database migrations. As a team we moved from Oracle to SQL Server and cut our monthly infra cost by roughly 50x.
Fixing things in production. After the cutover I tracked down index fragmentation, stale statistics, timeouts and deadlocks while the system was live.
Async & background jobs. I set up background work and messaging with RabbitMQ and Hangfire.
Integrations. I've built backends that talk to external systems like IBS and Pribas.
CI/CD & cloud. I moved our manual IIS deployments to Azure and automated them with CI/CD pipelines.

2,500+

dealers served by the portal

~50x

lower monthly infra cost

95%

faster passenger purchases

internal products in parallel

Experience

Click a project to expand.

Software Engineer · ID3 Software

Mar 2023 — Present

Yıldız Holding — SEC Market Dealer PortalSep 2023 — Present

I work on a dealer portal used by 2,500+ dealers across Turkey.
As a team we rebuilt the infrastructure and moved from Oracle to SQL Server, cutting monthly infra cost by ~50x. I was hands-on throughout the migration.
After the cutover I tracked down and fixed production issues: index fragmentation, stale statistics, query timeouts and deadlocks.
I build background jobs and async messaging with RabbitMQ and Hangfire on .NET Core.

SunExpress — Internal Operations ProductsJul 2023 — Sep 2023

I worked on 7 internal apps used by different departments, all at the same time.
I shipped new features while keeping the existing systems running.
Every department needed something different, so I sat down with each team to figure out what they actually needed.
I aimed for solutions that would hold up long-term rather than quick patches.
The apps ended up more stable and easier to maintain.

SunExpress — Airport Payment DeviceDec 2022 — Jul 2023

I owned the backend from the first line of code to the production deploy.
I designed and built the backend that integrates with external systems like IBS and Pribas.
Built it on .NET Core with performance and reliability as the main goals.
Designed the database and tuned the queries on MS SQL Server.
Deployments started out manual on IIS. Later I moved them to Azure and automated them with CI/CD pipelines.
In the end, passenger purchases got 95% faster.

Software Engineer Intern · ID3 Software

Jul 2022 — Mar 2023

Petroleum Development OmanInternship

I was involved in every stage, from development to going live.
Built the internal presentation and reporting screens used across the company.
Worked with .NET MVC and MS SQL Server.

Kızılay Migrant CardInternship

Tracked and fixed the bugs reported by the test teams before go-live.
Closed out critical issues so the project was ready to go live.

Projects

A research project from my university years.

Graph-Database B2B Platform for Supply ChainTÜBİTAK 2209-B

We built a B2B platform that makes it easier to find the right supplier in industrial procurement.
Suppliers are scored on financial status, technical competence, error rate, experience and reliability.
We used the PROMETHEE multi-criteria decision method for the ranking.
I applied KNN-based classification and distance scoring to analyze company–supplier relationships.
Supplier–buyer relationships were modeled in a graph database.
Companies could find the best-fit supplier based on past behavior, faster and cheaper.

Skills

Mostly .NET, async work and relational databases.

.NET Core.NET MVCRESTful APIs MS SQL ServerOracleRabbitMQ HangfireMicrosoft Azure Backend ArchitectureAsync & Background Processing Database MigrationRelational Database Design Query OptimizationPerformance Optimization CI/CD PipelinesIIS Deployment Application ScalabilityRefactoring Complex Business Logic Graph-Based Data Modeling

Education

school: Karadeniz Technical University
degree: Software Engineering
cgpa: 3.21

Get in touch

If you'd like to talk about backend, .NET or databases, just drop me a message.

Email me → LinkedIn

Berkay Hellagünbuilds fast, scalable backend systems on .NET.