Senior .NET / C# Backend Developer

The Role
You will be the primary backend engineer on our Med Spa Practice Management Platform, working alongside our .NET Modernization Lead and Frontend Modernization Engineer. Your focus is migration execution, integration work, and hardening — you'll be shipping the day-to-day port from legacy .NET Framework to .NET 8/9, moving Azure services to AWS equivalents, and maintaining PHI encryption and per-tenant isolation through every step.
You should be comfortable working across the full backend stack: EF6→EF Core migrations, Autofac→Microsoft DI refactoring, WebJobs→Lambda/EventBridge rewrites, Azure Service Bus→SQS/SNS/EventBridge porting. If you've done partial modernizations before and want to be part of a full end-to-end one, this role is designed for you.
What You'll Do
Ship the tablet-based clinic check-in/checkout backend to complete internal launch on the legacy stack
Execute project-by-project migrations from .NET Framework 4.5-4.6 to .NET 8/9 as the Lead sequences them
Port ASP.
NET MVC 5 / Web API 2 controllers and services to ASP.
NET Core
Migrate EF6 code-first data access to EF Core, preserving DB-per-tenant patterns
Refactor Autofac 3 registrations to Microsoft.
Extensions.
DependencyInjection
Port Azure WebJobs to AWS Lambda or ECS + EventBridge Scheduler
Migrate Azure Blob to S3, Azure Service Bus / Queues to SQS/SNS/EventBridge, Azure Redis to ElastiCache
Maintain and extend HIPAA field-level PHI encryption using AWS KMS
Move secrets to AWS Secrets Manager
Extend existing Authorize.
Net payment integration; evaluate and integrate physical card-processing hardware
Maintain existing Twilio (SMS) and SendGrid (email) integrations
Migrate logging from log4net + Application Insights to Serilog + CloudWatch + OpenTelemetry
Write and maintain xUnit/NUnit test coverage; raise coverage during migration
Contribute to code reviews and architectural discussions
Yêu cầu:
Required Experience
5+ years of professional C# / .NET development
Hands-on experience with both modern .NET (.NET 6/7/8) AND legacy .NET Framework 4.x production code
Real migration experience — you've participated in or led .NET Framework → .NET Core migrations, or ASP.
NET MVC 5 → ASP.
NET Core migrations
Entity Framework 6 → EF Core migration experience
Strong backend fundamentals: REST API design, dependency injection, async/await, Entity Framework
Solid SQL Server production experience
Proven API integration experience across payment providers, SMS providers, email providers, or cloud storage APIs
Testing discipline as a default (xUnit, NUnit, or MSTest + Moq)
Solid written English
Nice to Have
Multi-tenant SaaS experience (subdomain-per-tenant, tenant resolution middleware, DB-per-tenant)
HIPAA compliance implementation experience — even partial is a strong plus
AWS production experience — ECS/Fargate, EKS, Lambda, S3, SQS/SNS/EventBridge, ElastiCache, RDS
Autofac → Microsoft DI refactoring experience
Authorize.
Net, Stripe, or similar payment provider integration
Twilio (SMS) or SendGrid (email) integration experience
PDF/document generation tooling
Docker containerization for .NET
Quyền lợi:
What We Offer
Salary: USD 3,000-4,200/month gross, paid monthly via Multiplier Technologies Vietnam (Employer of Record)
13th-month bonus (1 month of salary, customary in Vietnam, paid every December)
Annual salary review with merit-based increases
Full Vietnamese statutory benefits administered via EOR: social insurance, health insurance, unemployment insurance, occupational accident and disease insurance
12+ days annual paid leave per Vietnamese Labor Code, plus all Vietnamese public holidays, plus sick and personal leave per Vietnamese Labor Code
Company-owned computer for your work
Access to our team space at Dreamplex, District 1 or District 3, Ho Chi Minh City
Company-provided VPN, MDM, security stack, and productivity software licenses
Direct mentorship from the US-based founder
Direct employment transition to Clearstone Software Vietnam Co., Ltd. planned for late 2026 / early 2027, with continuity of service preserved
Working Arrangement
Hybrid: 2-3 days per week at our HCMC team space (District 1 or 3), remainder home-based
Core overlap hours: 9:00 AM - 1:00 PM ICT for standup and synchronous work
Output-based culture — we value what you ship, not hours-in-chair
Initial 60-day probation via EOR, then indefinite-term contract
Application Process
Sen your CV (PDF)
Link to your GitHub profile or technical portfolio
Short cover note (3 paragraphs max): why you're interested, a specific .NET Framework → .NET Core or EF6 → EF Core migration you've worked on, and your approach to maintaining production stability during coordinated migration work
Earliest start date and current salary expectation in USD/month
Process timeline: ~3 weeks from application to offer.