Nilanjan Nath

Backend engineer with ~2 years of experience building payments, ticketing and infrastructure systems in Python, Django and PostgreSQL. As a founding engineer at Reker (Evolvevol Tech), took a metro-booking backend from first commit to production: ONDC integration with Namma Metro (BMRCL), Cashfree payments and refunds, T+1 settlement reconciliation, prepaid passes, and the CI/CD and cloud infrastructure it runs on. Also designed, built and deployed BurpnBill, a multi-tenant QR ordering and billing product for cafés, as a solo freelance developer, now live in 2 restaurants.

SDE-1, Founding Engineer at Evolvevol Tech Pvt. Ltd. (Reker) (2024-11 – 2026-09)

Metro ticketing and green-mobility app | one of two backend engineers for most of the tenure

• Built the Django/DRF backend behind the ONDC (TRV11) metro-booking flow for Namma Metro (BMRCL): search, select, init, confirm, cancel and refunds, with a companion Flask service for ONDC request signing and callbacks. Serves ~300 tickets a day and 10,000+ bookings since the May 2026 launch.
• Integrated Cashfree for payments, refunds and payouts, with webhook signature verification and idempotent handling of retries and duplicate callbacks.
• Designed and built a T+1 reconciliation and settlement system that groups each day's paid bookings into a batch, pays BMRCL through Cashfree Payouts and triggers ONDC receiver reconciliation. Batch IDs are derived and enforced by a unique (date, sequence) constraint, so a day can never be paid twice. Failed batches release their bookings for the next run.
• Fixed a production issue where paid users never received tickets: moved booking confirmation from the app to a server-side Celery task triggered by the payment webhook, with retries, automatic refund on failure, and a 5-minute orphan-recovery sweep.
• Built the pass system: a prepaid Namma Pass wallet, ride packs, and time-bound Daily and Weekly Saver passes with ticket caps and queued activation. Fixed ride-pack race conditions with row-level locking (select_for_update) and moved session expiry to ETA-scheduled Celery tasks. Added GST-split invoices emailed on purchase.
• Wrote a Redis token-bucket rate limiter (atomic Lua script, in-Redis clock, live-editable rules from Django Admin, fail-open) that protects the OTP, login and payment routes. Pre-auth routes are keyed by target mobile or email rather than IP, which stops OTP bombing and avoids locking out shared NATs.
• Built metro ride-streak rewards (with cancellation handling) and user blacklisting, and split a monolithic views module into packages to make debugging easier.
• Moved source control from GitHub to a self-hosted GitLab CE instance on Azure and wrote the upgrade, rollback and cloud-migration runbook. Replaced GitHub Actions with Jenkins pipelines (push to main deploys staging; merge to master deploys production, with migrations run on each deploy).
• Dockerized the Django, Flask, Celery and Redis services and provisioned and operated the Azure and VPS hosts for staging and production. Stack: PostgreSQL/PostGIS, Redis, Celery, Gunicorn.

SDE Intern at Y4E (Yclept 4E Labs) (2024-01 – 2024-06)

• Built Django REST APIs connecting front-end and back-end systems, with PostgreSQL for application data.
• Built Android features in Java with Retrofit to consume the APIs, including Google Maps integration for location features.

Bachelor of Computer Applications – Assam Downtown University, Guwahati (2021-08 – 2024-06)