Jerzy Kołosowski
C# Tech Lead · Warszawa, Poland
Bio
I'm a seasoned software developer and tech lead with over 16 years of experience designing and shipping scalable solutions across many industries. My current focus is cloud platforms at large scale: I lead a team at Symfonia Sp. z o.o. building applications in ASP.NET 8 on Azure (including AKS for production workloads).
I have a strong background in .NET, microservices, and integrating with third-party platforms — most recently I built the foundations for the team that now ships Polish KSeF (e-Invoicing) integration.
I've thrived in dynamic environments — from smart-metering systems to e-commerce and education platforms. I enjoy mentoring teams and ensuring we deliver high-performing, reliable tools that scale.
In my own time I dive into cryptography, IT security, and Linux, often experimenting with IoT and maintaining personal projects on custom Linux systems. You'll typically find me improving my technical and cloud skills and embracing new challenges.
Experience
Symfonia Sp. z o.o. — Team Leader / Tech Lead
June 2021 – Present · Warszawa
- Lead an IT team running multiple platform initiatives across the company.
- Deliver infrastructural and shared building blocks for applications written by other teams — particularly inter-application messaging.
- Stack: ASP.NET 8/6, GraphQL, Dapr, Azure (Azure SQL, Azure DevOps, Azure Blob Storage, Azure Service Bus, Azure Functions, AKS).
- Co-own the platform architecture; lead the implementation team and oversee releases and performance testing for a target scale of 50,000 customers.
- Co-developed the SSO authentication subsystem (ASP.NET 6, GraphQL, React, SQL Server).
- Provide platform support for the team building KSeF integration (Polish National e-Invoicing System), whose foundations I designed before handing it over.
- Drive observability/logging tooling: Azure Application Insights, Grafana.
- (Earlier: Programista Azure at Symfonia, June 2021 – August 2022 — built the KSeF communication module: ASP.NET 6, GraphQL, Kubernetes, Azure SQL, Hangfire, Azure Service Bus, Azure DevOps; implemented Szafir / KIR qualified-signature authentication.)
Networked Energy Services (NES) Corporation — Senior C# Developer
April 2020 – May 2021 · Warszawa
- Smart-metering platform managing tens of thousands of devices on-premises.
- Implemented KMIP (Key Management Interoperability Protocol) support for hardware Key Management Service.
- Maintained and refactored legacy .NET Framework + SQL Server / EF Core code while introducing new functionality.
- Side project: DLMS meter support in Python and C++.
- Worked in an international Scrum team (PL/UK/US/DE) — all in English.
British Council — Senior .NET Developer
May 2019 – March 2020 · Warszawa
- Exam-organisation platform — front-end in Angular and React, back-end in ASP.NET Core + SQL Server + Entity Framework.
- Microservices architecture, monorepo, full CI/CD ownership.
AZA Group SA — Senior Software Developer
March 2018 – April 2019 · Warszawa
- Store Catalog: high-throughput product backend for storefronts (.NET Core 2.0, MongoDB, RabbitMQ).
- Microservices for an e-commerce engine (.NET Core 2.2, MongoDB, Azure Functions, Docker, PostgreSQL).
ITMAGINATION Sp. z o.o. — Senior Software Developer C#
April 2015 – March 2018 · Warszawa
- Modular ERP application: ASP.NET MVC, NHibernate, custom framework. Scrum.
Koalicja na rzecz Polskich Innowacji — Senior Software Developer
August 2017 – February 2018 · Warszawa
- Blockchain workshops project — Ethereum-integrated meetup app.
- Solidity smart contract + UI in Angular 5 / TypeScript / Material Design.
DB Schenker Sp. z o.o. — Senior Software Developer C#
July 2014 – February 2015 · Warszawa
- WPF application for business customers ordering parcel delivery; .NET Framework, NHibernate, SQLite. Scrum.
Sollertes — Marcin Markowski — Software Developer C#
June 2011 – February 2015 · Warszawa
- Modular web-application framework on top of ASP.NET MVC + a custom database layer.
- CRM integrated with an online shop (custom framework).
- Financial-data analysis app on ASP.NET MVC; co-designed hardware infrastructure.
Newitech Sp. z o.o. — Software Developer C++
April 2008 – June 2011 · Warszawa
- BPM application maintained and extended in MFC.
- Application supporting high-school exams.
Education
Polish-Japanese Academy of Information Technology (Polsko-Japońska Wyższa Szkoła Technik Komputerowych)
Computer Science, BSc · Programming Business Applications · 2007 – 2013
(Studies completed without thesis defence.)
Certifications & training
- The Power of GenAI on AWS — 2024 (subscribed)
- Microsoft Certified: AZ-204 Azure Developer Associate — March 2021
- Blockchain workshops, Fundacja Koalicja na rzecz Polskich Innowacji — 2017–2018
Technical skills
- C# — up to C# 8.0+, ASP.NET, C++/CLI, Dapr
- Cloud — Azure (B2C, AKS, Application Insights), AWS (Lambdas)
- C/C++ — MFC
- Containers — podman, docker, docker-compose, Kubernetes, OpenShift
- Linux — nginx, zsh, bash, Python (basic)
- Web — HTML, JavaScript, React (basic)
- Databases — Azure SQL, Azure Cosmos DB (Mongo API), Microsoft SQL, PostgreSQL, MySQL, Oracle, SQLite, NHibernate (QueryOver), Redis
- Network stack — nmap, tcpdump, SSL/TLS (certificates, PSK), VPN (IPsec/IKEv2, Tinc)
- IDE — JetBrains Rider, Visual Studio, ReSharper
- Dev platforms — Azure DevOps, Atlassian ecosystem, Mantis, GitLab (self-hosted)
- VCS — Git
Languages
- Polish — native
- English — B2
Hobbies
- Cryptography & IT security — PKI, YubiKey, GPG (keybase.io/jkolo), Qubes OS
- IoT — Home Assistant, ESPHome, Zigbee, DIY firmware (esp-idf, Arduino)
- Linux — laptop on Arch, home server on Gentoo, OpenShift cluster on Raspberry Pi 4
- Sport shooting
Wyrażam zgodę na przetwarzanie moich danych osobowych dla potrzeb niezbędnych do realizacji procesu rekrutacji (zgodnie z Ustawą z dnia 29.08.1997 roku o Ochronie Danych Osobowych; tekst jednolity: Dz. U. 2016 r. poz. 922).