Principal C#/.NET Engineer

Will start 100% on site for 30 days & move to hybrid 3 days onsite 2 days remotePosition SummaryWe 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.Key ResponsibilitiesC# / .NET EngineeringRefactor machine-converted, COBOL-derived C# into idiomatic, maintainable .NET — meaningful naming, proper OO/domain design, separation of concerns, dependency injectionWork 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 UIRefactor legacy batch/procedural logic (converted from COBOL/JCL) into maintainable, testable .NET; handle exact decimal/financial arithmetic (decimal, rounding rules) to preserve benefit-calculation correctnessOptimize performance to meet the nightly batch window (profiling, memory management, async I/O, parallelism where safe)Entity Framework / Data LayerOwn 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 modelDesign 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 operationsManage EF Core migrations, concurrency handling, transactions, and connection resiliencyMap legacy data types and semantics correctly (packed decimals, fixed-width, EBCDIC-origin data, condition codes) to PostgreSQL/EF types without behavioral driftContribute to the COBOL-field → PostgreSQL-column → business-term data dictionaryTechnical LeadershipDefine and enforce C#/.NET coding standards, architecture patterns, and refactoring guidelines for the engineering teamServe as senior technical authority on the converted codebase; make cross-cutting design decisionsMentor mid/junior C# developers; perform code reviews; drive engineering qualityPartner with the Technical Manager/Architect on target architecture and the refactoring strategyQuality, Testing & DeliveryEnsure functional equivalence: build unit and regression tests (xUnit/NUnit, Moq) to validate refactored code against the legacy baseline; fix FET-surfaced defectsIntegrate 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 decisionsRequired Qualifications12-15 years of professional C#/.NET software engineering, including senior/lead responsibilitiesDeep expertise in C# and the .NET platform (.NET Framework and .NET Core / .NET 6/8+), including async programming, memory/performance optimization, and modern language featuresExpert-level Entity Framework / EF Core: entity modeling, Fluent API, migrations, query optimization, transactions, concurrency, provider-specific behaviorStrong relational database skills; PostgreSQL strongly preferred (Oracle/SQL Server acceptable) — schema design, indexing, query tuning, stored proceduresASP.NET Core Web API design (REST) for front-end integrationSolid software design: SOLID, design patterns, domain modeling, layered/clean architecture, dependency injectionTesting discipline: unit/integration/regression testing frameworks; TDD/mockingGit, CI/CD, and static code analysis (SonarQube)Proven ability to read, reason about, and safely refactor large, unfamiliar codebasesExceptional attention to correctness — financial/benefit calculation accuracyPreferred / Nice to HaveLegacy modernization experience — COBOL-to-C#/Java conversion, mainframe migration, or automated-transformation toolingUnderstanding of mainframe concepts (COBOL, JCL, batch processing, hierarchical/CODASYL databases like IDS-II/IMS) — to reason about source behaviorHigh-volume batch processing performance tuningAWS 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 domainsNpgsql specifics, EF Core performance internals, or ORM migration experienceSuccess in the First 90 DaysEstablish the C#/.NET and EF Core standards, patterns, and reference implementation the team will followRefactor a representative set of converted programs (including a benefit-calculation and a batch program) to clean, tested, performant C# validated against the legacy baselineDefine the EF Core data-access approach against PostgreSQL, including query-performance guardrails for batch workloadsMentor the team and set the code-review/quality bar