C#/.NET Engineer modernizing Cobol to C#/Net - Must be Local

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

Hello,

Job Title C#/.NET Engineer

Location- Hamilton, NJ Hybrid)

Duration 12+ Months Contracts Highly Chance to Extend

Job Description

We are looking for a C#/.NET Engineer to lead the modernization of a mission-critical legacy benefits system hosted on AWS Cloud. in Hamilton, NJ.

*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

We are modernizing a large, mission-critical Honeywell Bull mainframe benefits system (FAMIS) converting ~1.5M lines of COBOL and ~160K lines of JCL to C#/.NET, migrating an IDS-II hierarchical database to PostgreSQL, and deploying on AWS. Converted code is delivered by an automated modernization vendor in an "as-is" state. This Lead/Principal role owns the refactoring of that converted code into clean, maintainable, high-performance, production-grade C#/.NET, defines the data-access architecture using Entity Framework Core against PostgreSQL, sets engineering standards for the team, and safeguards functional equivalence to the legacy system. This is a benefits system serving NJ families correctness, performance within the nightly batch window, and maintainability are paramount.

What You'll Do

• Refactor machine-converted, COBOL-derived C# into idiomatic, maintainable .NET meaningful naming, proper OO/domain design, separation of concerns, dependency injection
• Work in .NET (Core) / .NET (latest version); apply modern C# language features (LINQ, async/await, records, pattern matching, nullable reference types, generics)
• Design and implement service layers, domain models, and APIs (ASP.NET Core Web API) that back the Angular UI
• Refactor legacy batch/procedural logic (converted from COBOL/JCL) into maintainable, testable .NET; handle exact decimal/financial arithmetic (decimal, rounding rules) to preserve benefit-calculation correctness
• Optimize performance to meet the nightly batch window (profiling, memory management, async I/O, parallelism where safe)
• Entity Framework / Data Layer:
• Own the data-access architecture using Entity Framework Core against PostgreSQL (Npgsql provider)
• Refactor the auto-generated/converted data-access layer into a clean, performant EF Core model
• Design entity models, DbContext configuration, Fluent API mappings, relationships, keys, and indexes reflecting the IDS-II PostgreSQL schema (168 tables, 4,024+ fields)
• Optimize EF Core queries (eager/lazy/explicit loading, projection, AsNoTracking, compiled queries, batching) to avoid N+1 and meet performance SLAs on high-volume batch operations
• Manage EF Core migrations, concurrency handling, transactions, and connection resiliency
• Map legacy data types and semantics correctly (packed decimals, fixed-width, EBCDIC-origin data, condition codes) to PostgreSQL/EF types without behavioral drift
• Contribute to the COBOL-field PostgreSQL-column business-term data dictionary
• Technical Leadership:
• Define and enforce C#/.NET coding standards, architecture patterns, and refactoring guidelines for the engineering team
• Serve as senior technical authority on the converted codebase; make cross-cutting design decisions
• Mentor mid/junior C# developers; perform code reviews; drive engineering quality
• Partner with the Technical Manager/Architect on target architecture and the refactoring strategy
• Quality, Testing & Delivery:
• Ensure functional equivalence: build unit and regression tests (xUnit/NUnit, Moq) to validate refactored code against the legacy baseline; fix FET-surfaced defects
• Integrate with CI/CD (AWS CodeBuild/CodePipeline), enforce quality/security gates (SonarQube, static analysis, secure coding/OWASP)
• Collaborate with FAMIS SMEs to preserve business logic (eligibility, benefit calculation, payments, EBT)
• Deliver incrementally within Scrum; document design and decisions

What You'll Need

Required

• 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

Preferred

• Legacy modernization experience COBOL-to-C#/Java conversion, mainframe migration, or automated-transformation tooling
• Understanding of mainframe concepts (COBOL, JCL, batch processing, hierarchical/CODASYL databases like IDS-II/IMS) to reason about source behavior
• High-volume batch processing performance tuning
• AWS experience (ECS/EKS, Lambda, RDS for PostgreSQL, S3, CloudWatch, IaC/CloudFormation)
• Experience integrating with enterprise job schedulers (Stonebranch, Control-M, CA7)
• Government / benefits / healthcare or other regulated, high-correctness domains
• Npgsql specifics, EF Core performance internals, or ORM migration experience