Available · full-time / contract · UK hoursRésumé ↓
live architecture
client → cloudflare → k8s gateway → services
hover the nodes
Available now · full-time, contract or project · UK hours overlap

Md. Nazmul Hasan Sarkar · Lead Software Engineer

I build systemsthat serve millions& think with AI.

15 years in backend — Node.js/TypeScript, Go and Python. I take multi-tenant SaaS from first schema to production, and I led a 40-million-user telecom from monoliths to microservices.

See the work →Book a call
15 yrsin production
40Musers served
−75%release time
−60%API latency
Case 01 — 40M-user telecom

One platform.
40 million people.

  1. The big pictureA national telecom platform for 40M users, moved off a monolith: edge → gateway → services, all on Kubernetes.
  2. Edge first: CloudflareEvery request from the mobile or web app lands on Cloudflare first — WAF, rate limiting, DDoS protection, Workers.
  3. API gateway on KubernetesGateway pods scale out behind the ingress. Each pod rate-limits, verifies the JWT against public JWKS, then proxies to the right service.
  4. Every service owns its dataIAM, UAM, profile, bonus and campaign services each talk to their own database. The gateway only talks to Redis and memory — JWKS fetched from the IAM service at boot.
  5. Campaigns reach phonesThe campaign service sends offers and OTPs through a third-party SMS provider, outside the cluster.
  6. Shipped on Kubernetes9 production apps on Docker and Kubernetes. Releases went from days to hours.
view: overview
gateway pods: 2
deploy: ~3 days → ~hours
Case 02 — Mavira · MyFitSize

AI that knows
when it's wrong.

  1. A request arrives“Make a product photo” · “Which size fits?”
  2. Route to the best modelClaude, GPT, Gemini, Flux or Veo — picked per task.
  3. Check every resultNothing reaches the user unverified.
  4. Fall back, deterministicallyWhen the model misreads a pet size chart, a rule engine takes over.
task: —
verdict: —
Selected work · 2021 — now

Things I've shipped.

Keep scrolling →Swipe the cards →

01 / 08AI content studio
5AI models, routed per task

Mavira

Credit-based studio for product photos, documents, and reports. Checks every result; bKash, Nagad, and card payments.

  • Multi-model LLMs
  • Image & video
  • Payments
02 / 08Shopify
4generation flows

AI Photoshoot

Multi-tenant product-photo SaaS: photoshoot, retouch, recolor, short video — pushed back to the store.

  • Fastify
  • Prisma
  • Redis
  • SQS
03 / 08size engine
3stage ranking pipeline

MyFitSize

Estimates measurements, matches the size chart, ranks variants. AI reads charts; rules catch its mistakes.

  • Vision
  • Ranking
  • Shopify
04 / 08identity
40Musers, signed in by SIM

IAM service

OAuth2/JWT identity for a multi-tenant telecom. SIM-based login issues short-lived JWTs; gateway pods verify them against cached JWKS.

  • NestJS
  • Go
  • OAuth2
  • JWKS
05 / 08pharmacy ops
0searching shelves by hand

RxDokan

Type a medicine, see the exact shelf and box — mapped from shelf photos. Multi-branch stock and expiry alerts.

  • Vision
  • Flutter
06 / 08distributor ledger
1Bangla ledger, not daily Excel files

Sorboraho

Photograph a slip or speak in Bangla; AI drafts rows for a person to approve. Offline Flutter app for field staff.

  • Speech
  • OCR
  • Offline
07 / 08Australia
−60%API latency

DevSuite

Three SaaS products for property developers on GCP and Kubernetes.

  • React
  • PostgreSQL
  • GCP
08 / 08EdTech
λevent-driven, serverless

TutsPaper

AI EdTech SaaS on API Gateway, Lambda, SQS, and DynamoDB. In development.

  • Lambda
  • SQS
  • DynamoDB
Experience

Fifteen years, one direction.

Apr 2026 — now

Lead Software Engineer

Red Circle Digital · remote
  • Built AI Photoshoot and MyFitSize for Shopify merchants, from design to production.
  • Size engine ranks variants; AI reads size charts with a rule-based fallback.
Dec 2025 — Mar 2026

Lead Software Engineer

Mind Orbital · remote
  • Built Hazira and Teamrail (NestJS, Angular); Kubernetes on DigitalOcean with Helm.
  • Stripe and SSLCommerz payments; background jobs on AWS SQS, Lambda, and Redis.
Apr 2023 — Sep 2025

Principal Software Engineer, Tech Lead

Astha.IT @ Banglalink
  • Led the 40M-user move from monoliths to NestJS and Go microservices; designed the IAM service.
  • Containerized 9 production apps (−75% deploy time); mentored 8+ engineers with code reviews and TDD.
Sep 2022 — Feb 2023

Senior Full-Stack Engineer

Apartments & Developments · Australia
  • Delivered 3 DevSuite SaaS products; cut API latency by about 60%.
Jan — Aug 2022

Senior Full-Stack Engineer

Bitstrapped · Canada
  • Analytics and data pipelines for the Canpath project on GCP.
Jun 2021 — May 2022

Senior Software Engineer

Strativ AB
  • Led a 5-person team on AllezPadel; built the backend from scratch with live game updates.
Aug 2018 — May 2021

Lead / Senior Software Engineer

SELISE Digital Platforms
  • Led MyCareerGate; built the JamAHook media player and AddExpert features.
2011 — 2018

Where it started

ECHO, ICT Euro, Impel IT, KaritKarma, Gonona, RS Software
  • PHP, Python, and Django to Node.js — e-commerce, shipping, and A/B testing tools.
Full résumé (PDF) ↓
Writing

Notes from production.

System Design

Designing an API gateway layer for tens of millions of users

Edge first, a stateless fleet of gateway pods, JWT verification with no network call, and services that own their data — the shape of a gateway that holds up at telecom scale.

Go

Go concurrency patterns I use in production services

Contexts that stop goroutines, bounded fan-out with errgroup, channel ownership, singleflight for expensive reloads, and the race detector in CI.

Node.js

The Node.js event loop, explained by the bugs it causes

Why one CPU-heavy handler slows every request, how the thread pool gets starved, and how to measure event-loop delay before your users feel it.

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Contact
Let's build
the next one.

Full-time, contract, or project work — can start right away, with UK business-hours overlap.

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