Senior .Net Engineer at N-iX in Poland

N-iX is looking for a Senior .Net Engineer for one of our clients. As a .NET Engineer you will drive the technical modernization of a large-scale system from .NET Framework 4.8 to .NET 8. Your work will span the full backend stack — replacing Windows-only dependencies, refactoring legacy patterns, migrating data access to EF Core, and ensuring every service is portable, containerizable, and ready for AWS cloud deployment. You will collaborate closely with DevOps and database engineers as part of a cross-functional Agile team delivering a phased, production-safe migration. Responsibilities: Migrate a .NET Framework 4.8 application to .NET 8. Migrate a large database-first Entity Framework 6 model to EF Core 8 across multiple bounded contexts, one domain at a time. Identify and replace Windows-only libraries and assembly references that prevent building and running on Linux. Establish unit test coverage measurement and enforce quality gates as part of the migration pipeline. Collaborate with the DevOps engineer on Dockerfile authoring, environment configuration, and secrets injection. Participate in Agile/SCRUM processes, conduct code reviews, and document migration decisions. Must-Have Qualifications: 5+ years of C# and .NET backend development with strong knowledge of ASP.NET and ASP.NET Core. Proven, hands-on experience migrating .NET Framework applications to .NET Core / .NET 8 in production. Solid experience with Entity Framework Core. Solid knowledge of DDD, CQRS, and repository patterns in layered .NET architectures. Familiarity with Docker multi-stage builds and Linux container fundamentals for .NET applications. Proficient with xUnit and Moq for unit testing; comfortable with container-wired test setups. Experience with AWS ECS / Fargate and ECR for deploying containerized .NET applications. Familiarity with MassTransit and RabbitMQ or Amazon MQ for event-driven messaging. Experience with Hangfire or similar background job processing frameworks. Proficient in Git and familiar with Agile/SCRUM team processes. Nice-to-Have Skills: Experience building CI/CD pipelines for .NET projects. Familiarity with micro-frontend architecture and Angular-based single-page applications. Experience with automated code coverage tooling and enforcing coverage thresholds in CI. Experience with performance optimization and scalable enterprise backend systems. We offer*: Flexible working format - remote, office-based or flexible A competitive salary and good compensation package Personalized career growth Professional development tools (mentorship program, tech talks and trainings, centers of excellence, and more) Active tech communities with regular knowledge sharing Education reimbursement Memorable anniversary presents Corporate events and team buildings Other location-specific benefits *not applicable for freelancers