Principal C#/.NET Engineer

Nexiva•Hamilton, NJ

1d•Hybrid

About The Position

The Principal C#/.NET Engineer will lead the modernization of FAMIS, a mission-critical New Jersey benefits system currently hosted on a Honeywell Bull mainframe. The project is converting approximately 1.5 million lines of COBOL and 160,000 lines of JCL to C#/.NET, migrating an IDS-II hierarchical database to PostgreSQL, and deploying the system on AWS. Converted code is delivered by an automated modernization vendor in an as-is state. This role owns refactoring that code into maintainable, high-performance, production-grade software; defines the Entity Framework Core data-access architecture; establishes engineering standards; and safeguards functional equivalence to the legacy system. Correctness, performance within the nightly batch window, and maintainability are paramount because the system serves New Jersey families. The role refactors converted COBOL-derived code into idiomatic .NET, develops service layers, domain models, and ASP.NET Core Web APIs that support an Angular UI, and transforms legacy batch and procedural logic into testable software. It requires careful handling of financial arithmetic and benefit calculations, as well as performance optimization for high-volume batch workloads. The engineer will own the EF Core architecture against PostgreSQL using the Npgsql provider, including entity and DbContext design, mappings, relationships, indexes, query optimization, migrations, transactions, concurrency, and connection resiliency. The work includes translating legacy data types and semantics without behavioral drift and contributing to a data dictionary connecting COBOL fields, PostgreSQL columns, and business terms. As a technical leader, the engineer will set coding and architecture standards, make cross-cutting design decisions, mentor developers, review code, and partner with the Technical Manager/Architect on the target architecture and refactoring strategy. The position also emphasizes unit, integration, and regression testing; CI/CD and quality/security gates; collaboration with FAMIS subject-matter experts; and incremental delivery within Scrum. The position is listed as hybrid in Hamilton, New Jersey. It starts 100% onsite for 30 days and then moves to three days onsite and two days remote. The posting lists a maximum rate of $60/hour C2C and prefers local candidates; relocation from a bordering state is acceptable.

Requirements

12–15 years of professional C#/.NET software-engineering experience, including senior or lead responsibilities.
Deep expertise in C# and the .NET platform, including .NET Framework and .NET Core/.NET 6/8 or later.
Experience with asynchronous programming, memory and performance optimization, and modern C# language features.
Expert-level Entity Framework/EF Core skills, including entity modeling, Fluent API, migrations, query optimization, transactions, concurrency, and provider-specific behavior.
Strong relational database skills, including schema design, indexing, query tuning, and stored procedures; PostgreSQL is strongly preferred, with Oracle or SQL Server acceptable.
Experience designing REST APIs with ASP.NET Core Web API for front-end integration.
Knowledge of SOLID principles, design patterns, domain modeling, layered or clean architecture, and dependency injection.
Experience with unit, integration, and regression testing frameworks, TDD, and mocking.
Experience with Git, CI/CD, and static code analysis such as SonarQube.
Proven ability to read, understand, and safely refactor large, unfamiliar codebases.
Exceptional attention to correctness, particularly for financial and benefits calculations.
Angular 17+, TypeScript, and Node.js experience.
Docker containerization and CI/CD pipeline experience, such as AWS CodePipeline or GitHub Actions.
AWS cloud-native application experience with services such as S3, SNS, SQS, ECS, RDS, EC2, or Lambda.

Nice To Haves

Legacy modernization experience, such as COBOL-to-C#/Java conversion, mainframe migration, or automated-transformation tooling.
Understanding of mainframe concepts such as COBOL, JCL, batch processing, and hierarchical/CODASYL databases such as IDS-II or IMS.
Experience tuning performance for high-volume batch processing.
AWS experience with ECS/EKS, Lambda, RDS for PostgreSQL, S3, CloudWatch, and infrastructure as code/CloudFormation.
Experience integrating with enterprise job schedulers such as Stonebranch, Control-M, or CA7.
Government, benefits, healthcare, or other regulated, high-correctness domain experience.
Npgsql expertise, EF Core performance internals, or ORM migration experience.

Responsibilities

Refactor machine-converted, COBOL-derived C# into idiomatic, maintainable .NET code using meaningful naming, object-oriented and domain design, separation of concerns, and dependency injection.
Use modern C# and .NET features, including LINQ, async/await, records, pattern matching, nullable reference types, and generics.
Design and implement service layers, domain models, and ASP.NET Core Web APIs that support the Angular UI.
Refactor converted COBOL/JCL batch and procedural logic into maintainable, testable .NET code.
Preserve benefit-calculation correctness by handling exact decimal and financial arithmetic, including rounding rules.
Optimize performance to meet the nightly batch window through profiling, memory management, asynchronous I/O, and safe parallelism.
Own the EF Core data-access architecture against PostgreSQL using the Npgsql provider.
Refactor the converted data-access layer into a clean, performant EF Core model.
Design entity models, DbContext configuration, Fluent API mappings, relationships, keys, and indexes that reflect the IDS-II-to-PostgreSQL schema.
Optimize EF Core queries and batch operations, avoiding N+1 queries and meeting performance SLAs.
Manage EF Core migrations, concurrency, transactions, and connection resiliency.
Map legacy data types and semantics, including packed decimals, fixed-width and EBCDIC-origin data, and condition codes, to PostgreSQL and EF types without behavioral drift.
Contribute to the COBOL-field-to-PostgreSQL-column-to-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 and make cross-cutting design decisions.
Mentor junior and mid-level C# developers, perform code reviews, and drive engineering quality.
Partner with the Technical Manager/Architect on target architecture and refactoring strategy.
Build unit and regression tests to validate refactored code against the legacy baseline and fix defects surfaced by FET.
Integrate with CI/CD and enforce quality and security gates, including static analysis and secure-coding practices.
Collaborate with FAMIS subject-matter experts to preserve eligibility, benefit-calculation, payment, and EBT business logic.
Deliver incrementally within Scrum and document design and technical decisions.
Within the first 90 days, establish C#/.NET and EF Core standards, patterns, and a reference implementation.
Within the first 90 days, refactor representative converted programs, including a benefit-calculation program and a batch program, and validate them against the legacy baseline.
Within the first 90 days, define the EF Core data-access approach against PostgreSQL, including query-performance guardrails for batch workloads.
Within the first 90 days, mentor the team and establish code-review and quality expectations.