C#/.NET Engineer

Our customer is modernizing a large, mission-critical Client 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. 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.

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C#/.NET Engineer Position Description

We are seeking a C#/.NET Engineer to join our team. The selected candidate will work onsite for the first 30 days and then will transition to a hybrid role consisting of three (3) days each week onsite in Hamilton Township, NJ and two (2) days each week remotely.

Summary:

Our customer is modernizing a large, mission-critical Client 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

Physical Demands:

Ability to safely and successfully perform the essential job functions consistent with the ADA and other federal, state, and local standards

Sedentary work that involves sitting or remaining stationery most of the time with occasional need to move around the office to attend meetings, etc.

Ability to conduct repetitive tasks on a computer, utilizing a mouse, keyboard, and monitor

***Please note that any false information on your resume or application could lead to the offer being withdrawn or even termination after hire.***