Headline

Software Engineer | Java, Spring Boot, Distributed Systems, AWS, Kafka, PostgreSQL | Building Payments & Ledger Infrastructure

About

Backend engineer (~2 years) building production payment and ledger systems in Java/Spring Boot. At Callisto Infotech, I shipped multi-tenant infrastructure serving 100K+ users — checkout, idempotent webhooks, 50K events/day pipelines, and observability for 8+ services. Outside work, I'm building a fintech-grade billing & payments engine (linked below): 21 domain modules, 970+ classes, 94 tables, double-entry ledger with DB-trigger-enforced immutability, 3-layer idempotency, transactional outbox with lease + heartbeat, ASC 606 revenue recognition, and 2000+ tests. It's me trying to learn how Stripe, Razorpay, and Adyen actually engineer financial correctness at scale. What I care about: correctness under concurrency, money math you can audit, systems you can operate at 3am. Stack: Java 17, Spring Boot, PostgreSQL, Redis, Kafka, Docker, AWS. C++ for competitive programming (700+ LeetCode, 250+ Hard, top 5% contests). Open to senior backend / SDE-2 roles in fintech, payments, or core infra. Bangalore or remote. https://github.com/ishwetraj17/payments-and-ledger-engine

Location

Bengaluru

AI stack

claude code

claude

cursor

openai

Work experience

Software Engineer at Callisto Infotech, Mar 2024 - Present · 2 yrs 9 mos, Remote, - Architected production multi-tenant backend across SaaS and e-commerce verticals for 50+ business clients, 100K+ end users, service isolation, fault boundaries, 40% fewer integration failures, launch cycles cut 6 weeks → 2 weeks. - Built payment integration end-to-end — checkout, order flow, webhook handling, and idempotent retry logic across 80+ endpoints. Zero double-charges, auth incidents cut from 20/year to near-zero, scaled to 100K+ users. - Engineered order/transaction event pipeline at 50K events/day, 500 events/sec peak with exactly-once semantics and Redis deduplication — zero dropped order events, 35% faster incident response. - Optimized 30+ data paths across order, catalog, and payment tables — composite + partial indexes, N+1 elimi- nation. p95: 500ms → 300ms, +30% throughput, handled 50% more load without scaling. - Built real-time observability layer with per-transaction audit trails — structured logging, distributed tracing, 500+ metrics across 8+ services. Incident resolution hours → 20 minutes, 10× faster RCA.

Software Engineering Intern at Callisto Infotech, Dec 2023 - Feb 2024 · 3 mos, On-site, - Shipped multi-threaded log ingestion system (Java) processing 500MB+ daily logs, zero loss. Throughput 50 → 75 MB/hr (1.5×), now powers all 3 verticals. - Designed lock-free concurrency patterns with formal lock ordering — 30% fewer failures, enabled safe con- current job scheduling. - Profiled and optimized heap/CPU hotspots (VisualVM, GC tuning) — 20% peak memory reduction, critical for real-time processing.

Education

Bachelor of Technology, Computer Science, University of Engineering & Management (UEM)

Senior Secondary (10+2), Resonance International School

Public links

github: https://github.com/ishwetraj17

leetcode: https://leetcode.com/ishwetraj2