David Leder | Portfolio

Projects

ISP management & billing system

Company: DuoBit

Role: Backend & Infrastructure Engineer

DuoBit is a telecommunications company based in Novi Sad, providing internet services, video surveillance systems, and computer hardware sales. They hired me to develop a full end-to-end system with the following features:
- A SQL database and .NET-based RESTful API with scheduled background tasks for daily automation, deployed on-site on Linux Ubuntu servers, keeping the system operational even during internet outages.
- Integration with the company's network infrastructure (MikroTik / RADIUS) to manage internet access for ~2,000 active users.
- An automated billing notification pipeline: overdue accounts trigger email and SMS reminders, with automatic service suspension for accounts that remain unpaid past the grace period.
- Git-based version control with a CI/CD pipeline for automated testing and deployment.
- An internal inventory management system for tracking computer hardware stock and sales.
- Automated PDF parsing of POS reports for direct data entry, removing the need for manual bookkeeping.
- An admin panel enabling staff to monitor active users, internet usage, and connection statuses across the network.
Fuel product & invoice management platform

Company: Innomatics | Product: eFuel Systems

Role: Full Stack Engineer (Backend focus)

eFuel Systems is a cloud-based SaaS platform developed by Innomatics (Australia) for centralised management of fuel retail, serving 32,000+ clients globally. I worked as a full stack developer contributing across the entire platform:
- Developed features end-to-end using .NET/C#, React, and MS SQL Server from database schema and RESTful API logic through to the final UI.
- Owned the invoice management microservice from database to frontend, giving finance teams real-time visibility into uploaded documents, processing status, and payment data.
- Built Azure Functions to automate manual work across the platform: sending emails, processing files, scraping third-party portals with Selenium, and syncing data with external services like Xero.
- Wrote automated tests for critical workflows so that new changes could be deployed confidently without breaking existing functionality.
- Worked in an Agile/Scrum team using Azure DevOps, Git, and CI/CD pipelines, with code reviewed by senior engineers before every merge.
Union member portal

Client: Syndical Organization of the Institute of Oncology of Vojvodina

Role: Full Stack Developer

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SOIOV is the trade union representing the staff of the Institute of Oncology of Vojvodina, one of the largest and most specialized oncology and research institutions in the region. They commissioned a public-facing website to inform members and manage union content online.
- Built the full stack from scratch using .NET 8, React, and PostgreSQL, with a RESTful API connecting the frontend to the database.
- Deployed the backend and server on a Linux VPS using Docker, with a Git-based CI/CD pipeline for automated testing and deployment, so updates can be shipped reliably without manual intervention.
- Built a password-protected admin panel so union staff can independently update all website content, news, announcements, and member information, without touching any code.
Business websites

Client: Metal Stil, Novi Sad

Static business website for a Novi Sad-based welding and metalwork company specialising in structural welding, custom gates, fences, and staircases. Built with plain HTML, CSS, and JavaScript, featuring an image gallery with lightbox, an embedded Google Maps location, and a contact form for customer enquiries. Custom domain setup pending.

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Client: Jastreb d.o.o.

Static business website for Jastreb, a company with 32+ years of experience distributing welding equipment and metallurgical products. Built with plain HTML, CSS, and JavaScript, with an embedded Google Maps location and a contact form for customer enquiries. Delivered with a custom domain.

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Client: Pro Dental Aesthetic

Static multi-language business website for an aesthetic dental clinic, presenting services, team information, and clinic details. Built with plain HTML, CSS, and JavaScript, with an embedded Google Maps location and a contact form for appointment enquiries. Delivered with a custom domain.

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About me

I'm a software engineer who moved into infrastructure and cloud development. My journey started with .NET and React, but as the years went by I started gravitating more towards automation and building systems that make other developers' jobs easier.

I spend most of my time below the surface: designing SQL databases, building RESTful APIs, writing automation for testing and logging, and setting up systems and pipelines. I've built and deployed multiple Linux-based systems, both in the cloud and on-site. Git, CI/CD, and Docker are a standard part of how I work.

Outside of employment, I've built and deployed several production systems as a freelancer too, handling everything from database and backend logic to server setup, domain configuration, and ongoing maintenance.