Job Description
Job Title: Lead/Principal C#/.NET Engineer – Mainframe Modernization & EF Core
Work Arrangement: Hybrid - 100% onsite for the first 30 days, then 3 days onsite and 2 days remote per week
Location: Hamilton, NJ
Contract Duration: 10+ Months
Interview: In Person
Position Summary
We are 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.
Key Responsibilities
C# / .NET Engineering
Work Arrangement: Hybrid - 100% onsite for the first 30 days, then 3 days onsite and 2 days remote per week
Location: Hamilton, NJ
Contract Duration: 10+ Months
Interview: In Person
Position Summary
We are 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.
Key Responsibilities
C# / .NET Engineering
- 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)
- 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
- 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
- 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
- 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
- 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
- Establish the C#/.NET and EF Core standards, patterns, and reference implementation the team will follow
- Refactor a representative set of converted programs (including a benefit-calculation and a batch program) to clean, tested, performant C# validated against the legacy baseline
- Define the EF Core data-access approach against PostgreSQL, including query-performance guardrails for batch workloads
- Mentor the team and set the code-review/quality bar
- C# Programming Experience
- .NET Core / .NET 6/7/8/10 Experience
- .NET REST/WEB API Development Experience
- Entity Framework Core and LINQ and async/await patterns Experience
- Solid software design: SOLID, design patterns, domain modeling, layered/clean architecture, dependency injection
- Angular 17+, Typescript and Node.js experience
- Strong relational database skills; PostgreSQL strongly preferred (Oracle/SQL Server acceptable) — schema design, indexing, query tuning, stored proc
- Unit/integration/regression testing frameworks; TDD/mocking
- Git and static code analysis (SonarQube)
- Docker containerization and CI/CD pipeline experience (AWS CODEPIPELINE OR GitHub Actions)
- AWS cloud native applications (S3, SNS, SQS, ECS, RDS, EC2, Lambda)
Numbers & Facts
| Location | Hamilton, NJ |
| Industry | Computer/IT Services |
| Company Size | 20 to 49 employees |
| Year Founded | 2002 |
| Website | http://crescensinc.com/ |
About Company
Crescens Inc. is an industry leader in providing IT staffing services and tailored workforce solutions to meet the demanding expectations and distinctive needs of clients across the United States and Canada. We have grown tremendously in the past years and have been applauded by our clients for the quality of workforce and the quick turnaround time. We have evolved from good service to great service and all management plans are geared towards quality.
Our vision is to be the best in Talent Acquisition and strive for excellence consistently by focusing on four performance dimensions; Quality, Efficiency, Cost and Risk. A satisfied client and candidate are the backbone to our continued success. Headquartered in New Jersey, we are a team with unique expertise to deliver exceptional results to our clients by setting benchmarks and establishing best practices.
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