AI System Design
Portrait of Sunny Kumar
About the creator

Sunny Kumar

Backend / Full-Stack Developer · NestJS · Node.js · TypeScript · Microservices

Patna, Bihar, India

Backend-focused full-stack developer with 4+ years of experience building multi-tenant SaaS platforms on NestJS, Node.js and TypeScript. I own complex backend systems end to end: multi-tenancy, RBAC, Keycloak/OAuth, Meta and WhatsApp integrations, subscription billing and event-driven microservices, on MongoDB and Redis, shipped with Docker and CI/CD.

Why I built AI System Design

Most system design material is static: a box-and-arrow diagram and a list of buzzwords. But the backend systems I work on every day (multi-tenant platforms, event-driven microservices, caches, queues and third-party integrations) only really make sense when you see them under load and watch what breaks. AI System Design is my attempt to teach system design that way: run the system, break it, then fix it.

Start learning →Read the theoryTry a design challenge

Experience

  1. Backend / Full-Stack Developer (NestJS · Angular)

    Jan 2024 – Present
    Kanlas Technologies · Patna, India
    • Built and scaled a multi-tenant SaaS backend on NestJS, TypeScript and MongoDB, with tenant isolation, agency/business/user hierarchies and an event-driven microservices architecture.
    • Engineered the Meta Graph API integration end to end: OAuth token flows, Facebook Page linking and permission scopes, Instagram Business connectivity and analytics aggregation.
    • Delivered WhatsApp Business onboarding via Embedded Signup on the WhatsApp Cloud API, with template management and webhook-driven messaging.
    • Secured the platform with Keycloak, OAuth 2.0 and role-based access control across multi-tenant roles.
    • Built subscription and billing: add-on location billing, AI credit metering, Razorpay payments and automated invoicing.
    • Connected services with Apache Pulsar events, used Redis for caching and sessions, and added real-time updates over WebSockets.
    • Containerised and deployed with Docker, Azure Container Registry and CI/CD in an NX monorepo, with MinIO for object storage.

  2. Software Developer

    Aug 2022 – Dec 2023
    Auditech Corp LLP · Gurugram, India
    • Built a large-scale RFID scanning app for warehouse operations, adopted by enterprise clients including Tata Motors, Mahindra and Voltas.
    • Implemented multi-threaded tag processing across Flutter and native Java for high-volume concurrent scans.
    • Developed two open-source Flutter plugins for UHF RFID hardware: RFIDC72Plugin and ZebraRFIDPlugin.

  3. Flutter Developer (Contract)

    2022 – 2023
    Sitesurface & Fello · New Delhi & Bengaluru, India
    • Developed and published 6+ cross-platform mobile apps on Google Play, from UI to REST API integration and release workflows.

Skills

Core backend
Node.jsNestJSTypeScriptREST APIsMicroservicesWebSocketsMongoDBRedis
Integrations & auth
Meta Graph APIWhatsApp Cloud APIInstagramGoogleRazorpayKeycloakOAuth 2.0RBAC
DevOps & cloud
DockerDocker ComposeAzure Container RegistryCI/CDMinIOApache PulsarNX Monorepo
Frontend
AngularAngular MaterialReactTailwind CSSHTMLCSS
Also
Express.jsJavaDartFlutterFirebaseC++

Education

Bachelor of Computer Applications (BCA)

Patliputra University, Patna

2019 – 2022

Achievements

  • Hacktoberfest 2023 contributor (Flutter / Dart)
  • 500+ DSA problems solved on LeetCode and other platforms

Get in touch

Feedback on the site, a bug, or a system you'd like to see added? Email me at roysunny951@gmail.com.