Seniorlead C#.NET Engineer

Sr/Lead C#/.NET Engineer
Location: Hamilton NJ (On site)

Position Type: Contract

In Person Interview

*Deep expertise in C# and platform (.NET Framework 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.

Job Description

We are looking for a C#/.NETEngineer to lead the modernization of a mission-critical legacy benefits system hosted on AWS Cloud. This position will be full-time and hybrid in Hamilton NJ.

What Youll Do

• Refactor machine-converted COBOL-derived C# into idiomatic meaningful naming proper OO/domain design separation of concerns dependency injection
• Work (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 ( Core Web API) that back the Angular UI
• Refactor legacy batch/procedural logic (converted from COBOL/JCL) into maintainable ; 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 4024 fields)
• Optimize EF Core queries (eager/lazy/explicit loading projection AsNoTracking compiled queries batching) to avoid N1 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 Youll Need

Required:

• 12-15 years of professional C#/.NET software engineering including senior/lead responsibilities
• Deep expertise in C# and platform (.NET Framework 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
• 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 stationary 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

Required Skills:

C#. Core / .NET 6/8PostgreSQLOracle/SQL Server Core Web API designGit CI/CDCOBOL-to-C#/Java conversionmainframe migrationAWSCS/EKS Lambda RDS for PostgreSQL S3 CloudWatch IaC/CloudFormationStonebranch Control-M CA7