Senior C#/.NET Lead for Benefits System Modernization

Zenosys; Hamilton (NJ); Hybrid; USD 140,000 - 210,000; Full time

Job summary

Zenosys in Hamilton, NJ is seeking a senior C#/.NET Engineer to lead modernization of a mission-critical legacy benefits system hosted on AWS. You will own refactoring of converted code into clean, scalable .NET, design EF Core data layer against PostgreSQL, and establish coding standards for the team.

Responsibilities include driving architecture, mentoring engineers, and delivering tests to ensure functional equivalence with the legacy system while meeting nightly batch performance goals.

Qualifications

• 12-15 years of professional C#/.NET software engineering, including senior/lead responsibilities.
• Deep expertise in C# and the .NET platform (.NET Framework and .NET Core / .NET 6/8+), including async programming, memory/performance optimization, and modern language features
• Expert-level Entity Framework / EF Core: entity modeling, Fluent API, migrations, query optimization, transactions, concurrency, provider-specific behavior
• Strong relational database skills; PostgreSQL strongly preferred (Oracle/SQL Server acceptable) schema design, indexing, query tuning, stored procedures
• ASP.NET Core Web API design (REST) for front-end integration
• Solid software design: SOLID, design patterns, domain modeling, layered/clean architecture, dependency injection
• Testing discipline: unit/integration/regression testing frameworks; TDD/mocking
• Git, CI/CD, and static code analysis (SonarQube)
• Proven ability to read, reason about, and safely refactor large, unfamiliar codebases
• Exceptional attention to correctness financial/benefit calculation accuracy

Responsibilities

• Refactor COBOL-derived code into idiomatic, maintainable .NET design with proper OO/domain modeling.
• Work in .NET (Core) / .NET (latest version); apply modern C# features.
• Design and implement service layers, domain models, and APIs (ASP.NET Core Web API) for the Angular UI.
• Refactor legacy batch/procedural logic into maintainable, testable .NET; ensure exact decimal/financial arithmetic.
• Optimize performance to meet the nightly batch window; memory management and async I/O.
• Own data-access architecture using Entity Framework Core against PostgreSQL (Npgsql).
• Refactor data-access layer into a clean EF Core model; design mappings, keys, indexes.
• Manage EF Core migrations, concurrency, transactions, and connection resiliency.
• Map legacy data types to PostgreSQL/EF types without behavioral drift.
• Contribute to data dictionary and engineering standards; lead technical decisions.
• Mentor junior developers; perform code reviews; drive quality.
• Collaborate with AWS-based deployment and CI/CD pipelines.

Skills

C#

NET Core/Framework

EF Core

ASP.NET Core Web API

PostgreSQL

AWS

Unit testing

CI/CD

Git

Performance tuning

Tools

Npgsql

SonarQube

Git

Job description

Zenosys in Hamilton, NJ is seeking a senior C#/.NET Engineer to lead modernization of a mission-critical legacy benefits system hosted on AWS. You will own refactoring of converted code into clean, scalable .NET, design EF Core data layer against PostgreSQL, and establish coding standards for the team.

Responsibilities include driving architecture, mentoring engineers, and delivering tests to ensure functional equivalence with the legacy system while meeting nightly batch performance goals.