08/22/2026 updated
100 % available
Senior Backend Engineer | C#/.NET | Financial Systems | Distributed Systems & Microservices
Warszawa, Poland
Only remote
Master of Computer Science, University of WarsawAbout me
Ich schätze saubere Algorithmen, Lesbarkeit und minimalistisches Design. Seit 2014 arbeite ich mit Microservices und Cloud-Technologien. Aktuell entwickle ich eine Banking-Plattform für Transaktionsverarbeitung und Buchhaltung – mit Fokus auf Sicherheit, Performance, Zuverlässigkeit und Tests.
C Sharp (Programming Language)Financial SoftwareNoSQLPerformance Engineering.NET CoreBackendOptimization AlgorithmsMicroservices
C# / .NET Development
Extensive expertise in C# and .NET Core for building high-performance backend systems, including financial accounting platforms, transaction processing, and core middleware for banking applications.
Distributed Systems & Microservices
Deep knowledge of distributed systems design and microservices architecture, including Event Sourcing, DDD, and Event-Driven Architecture, applied in large-scale financial and banking environments.
Cloud Technologies (Azure)
Hands-on experience with Azure services including Azure Service Bus, Azure Event Hubs, Cosmos DB, Azure Application Insights, and Azure DevOps for monitoring, performance analysis, and cloud-native development.
Performance Engineering & Optimization
Proven track record in performance and memory optimizations, such as reducing daily balance storage requirements by 96%, and improving request response times from 30 seconds to under 1 second.
SQL & NoSQL Databases
Proficiency with SQL Server, MongoDB, PostgreSQL, and Cosmos DB for data management in complex financial and enterprise systems.
Automated Testing & TDD
Strong focus on test-driven development and automated testing, including full automated test coverage from scratch and extensive use of TDD and DDD methodologies.
API Design & Integration
Experience designing and implementing PSD2 APIs for Open Banking, OAuth 2.0, gRPC, WCF, and integrations with external enterprise systems such as SAP, IBM, and Oracle.
DevOps & Monitoring
Practical use of GitHub Actions, Azure DevOps, Docker, Grafana, and Azure Application Insights for CI/CD pipelines, infrastructure monitoring, and performance dashboards.
Team Leadership & Architecture Design
Experience leading development teams of up to 9 people, conducting technical analyses, architecture design, and coordinating cooperation with business stakeholders and external systems.
Angular & Frontend Integration
Knowledge of Angular and Blazor for frontend integration within full-stack backend-focused projects, including complex JavaScript widgets and UI components.
Extensive expertise in C# and .NET Core for building high-performance backend systems, including financial accounting platforms, transaction processing, and core middleware for banking applications.
Distributed Systems & Microservices
Deep knowledge of distributed systems design and microservices architecture, including Event Sourcing, DDD, and Event-Driven Architecture, applied in large-scale financial and banking environments.
Cloud Technologies (Azure)
Hands-on experience with Azure services including Azure Service Bus, Azure Event Hubs, Cosmos DB, Azure Application Insights, and Azure DevOps for monitoring, performance analysis, and cloud-native development.
Performance Engineering & Optimization
Proven track record in performance and memory optimizations, such as reducing daily balance storage requirements by 96%, and improving request response times from 30 seconds to under 1 second.
SQL & NoSQL Databases
Proficiency with SQL Server, MongoDB, PostgreSQL, and Cosmos DB for data management in complex financial and enterprise systems.
Automated Testing & TDD
Strong focus on test-driven development and automated testing, including full automated test coverage from scratch and extensive use of TDD and DDD methodologies.
API Design & Integration
Experience designing and implementing PSD2 APIs for Open Banking, OAuth 2.0, gRPC, WCF, and integrations with external enterprise systems such as SAP, IBM, and Oracle.
DevOps & Monitoring
Practical use of GitHub Actions, Azure DevOps, Docker, Grafana, and Azure Application Insights for CI/CD pipelines, infrastructure monitoring, and performance dashboards.
Team Leadership & Architecture Design
Experience leading development teams of up to 9 people, conducting technical analyses, architecture design, and coordinating cooperation with business stakeholders and external systems.
Angular & Frontend Integration
Knowledge of Angular and Blazor for frontend integration within full-stack backend-focused projects, including complex JavaScript widgets and UI components.
Experience
Professional experience10+ years
Freelancer since2018
Languages
GermanBasic knowledgeEnglishFluentPolishNative speaker
Project history
Migration of 2.5M accounts to a new accounting platform. Technical analysis including gap detection based on extensive automated testing. Logical adjustments requiring extensive domain knowledge and a deep understanding of technical details. Performance impact analysis covering key areas of transaction processing and accounting.
Historical Debits: support for interest calculation. A high-performance service responsible for maintaining and reconstructing the historical state of the main Ledger, including retroactive changes such as refunds and payment reversals. Complex accounting logic with a strong focus on linear computational complexity (O(N) with respect to stream size) and memory efficiency, using a diff-based storage model.
Core financial accounting platform covering transaction processing, Ledger management, financial reporting, credit allocation, end-of-day processing, data migration, and support for interest calculation. Performance and memory optimizations including reducing daily balance storage requirements by 96%. Monitoring and performance analysis using Azure Application Insights and Grafana dashboards. Technologies: .NET Core, Cosmos DB, Azure Service Bus, Event Sourcing, OOP, TDD, DDD.