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Lead/Principal C#/.NET Engineer – Mainframe Modernization & EF Core
Crescens Inc.
- 🇨🇦 Canada | 🇺🇸 United States
- On-site
- Staff / Principal
- 7 hours ago
- C#
- .NET
- COBOL
- PostgreSQL
- AWS
- Entity Framework
- .NET Core
- ASP.NET Core
- Angular
- xUnit
- NUnit
- CI/CD
- SonarQube
- OWASP
- Scrum
- .NET Framework
- Oracle
- TDD
- Git
- Java
- ECS
- EKS
- RDS
- CloudWatch
- IaC
- CloudFormation
- Core Data
- TypeScript
- Node.js
- Docker
- GitHub Actions
- AWS Cloud
- SNS
- SQS
- EC2
7 hours ago
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)
Lead/Principal C#/.NET Engineer – Mainframe Modernization & EF Core · Crescens Inc.