Fullstack Developer (Backend focus Java, .NET, NodeJS)

Job Description – K&M Holdings Job title: Fullstack Developer (Backend focus)Location: Truong Cong Giai, Cau Giay, Hanoi, VietnamTerms: Full-timeSalary/rate: Up-to $1750 plus benefits Proposition: • JOB OFFER after 1 ROUND INTERVIEW• Mentorship by seasoned Tech Leads & free access to modern learning courses• While NOT mandatory, strong English reading/listening skills are highly recommended for ongoing course learning & documentation reviewAbout us: K&M Holdings is a dynamic startup in Hanoi specializing in SaaS/AaaS solutions. Our flagship products include an IP Telephony platform built on Asterisk, a coalition loyalty app, and AI-powered customer care agents.About the role:In this role, you will be responsible for building core backend services for our products from feature-oriented logic to API instrumentation, metering pipeline, pricing logic and expose aggregated usage data for DevOps team. Additionally, you might be required to get involved in frontend development using standard frameworks.Responsibilities: • Write clean, maintainable backend code in backend-focus tech stacks (NodeJS, Java, C#, Go…). Use modern frameworks (e.g. Express, Spring Boot) and database technologies (SQL/NoSQL) to build scalable services. Participate in design reviews and maintain high code quality.• Work closely with product managers, QA, frontend engineers, and a dedicated DevOps team. Focus on application logic – the DevOps team handles deployment, CI/CD, and infrastructure.• Instrument and record resource usage (API requests, token counts, compute time) for each customer and license. Build automated reporting to summarize usage for customers and internal finance teams.• Develop customer-facing and internal APIs or microservices for usage and billing data. Ensure usage data flows securely between on-prem or client deployments and the central billing system.• Implement enterprise licensing features such as license key validation and enforcement of subscription terms. Support flat subscriptions alongside consumption tiers, and handle on-premise deployments that periodically report usage back to the cloud for billing.• Develop and maintain the web application and occasionally contribute to mobile app development using cross-platform frameworks.