Java 21 + Spring Boot router with regex routing, three balancing strategies, hand-rolled circuit breaker, token-bucket rate limiter, and live WebSocket telemetry. Validated at 10K+ RPS, p99 < 20 ms, ~210 MB resident.
lekhrajkumar
Backend Software Engineer. 5+ years owning high-throughput distributed systems in payments & SaaS. Hands-on with React when the UI is the bottleneck.
Note: this portfolio ships live edge endpoints — /api/health and /api/stats. Open them.
- deploy2024appdirect/billingMigrated RabbitMQ → Kafka (4× throughput)
- ship2025router-service10K+ RPS sustained, p99 < 20ms
- publish2026case-studies/router-serviceWrote up tradeoffs and outcome
Owner
Who runs this service. Bio, education, signals, and the engineering principle I keep coming back to.
I'm a Software Engineer with 5+ years building and scaling high-throughput distributed systems in payments, SaaS, and retail-tech.
At CP Axtra, I'm building backend microservices for a payment-related invoice processing system — reactive WebFlux, Kafka event pipelines, Keycloak OAuth2, distributed ShedLock schedulers, and a Testcontainers integration framework targeting 75% instruction coverage.
Previously at AppDirect I designed and owned high-availability microservices for Billing, Checkout, Notifications, and Payments — supporting thousands of concurrent requests with sub-200ms p99 latency. I led the migration from RabbitMQ to Kafka, achieving a 4× throughput improvement for billing workflows processing millions of events per day.
My core expertise spans microservices architecture, event-driven systems, JVM performance tuning, and building production-grade observability stacks with Prometheus and Datadog APM.
B.Tech + M.Tech · Electronics & Communication
2015 – 2020
Great systems aren't just fast — they're observable, resilient, and maintainable. I build for the 3am incident, not just the happy path.
— principle
- ›Building Invoice Management System at CP Axtra
- ›Writing case studies for shipped systems
- ›Senior Software Engineer · CP Axtra
Stack & tooling
What this service runs on. Primary tags marked with a leading dot.
- Java
- Golang
- JavaScript
- TypeScript
- SQL
- Spring Boot
- Spring Security
- Hibernate / JPA
- RESTful APIs
- GraphQL
- WebSockets
- OAuth2
- Spring AI
- OpenAI / GPT
- Anthropic / Claude
- Cohere
- Groq
- Ollama
- RAG
- Prompt Engineering
- Microservices
- Event-Driven
- Domain-Driven Design
- System Design (HLD/LLD)
- SaaS Platforms
- Apache Kafka
- RabbitMQ
- PostgreSQL
- MySQL
- MongoDB
- Redis
- AWS
- Docker
- Kubernetes
- Helm
- GitHub Actions
- Jenkins
- Prometheus
- Datadog APM
- Spring Actuator
- Elasticsearch
- Logstash
- Centralized Logging
- JUnit
- Mockito
- Integration
- Contract
- TDD
- CI/CD Pipelines
Deployment history
Where this engineer has shipped. Newest deploy first. Click a row to expand the changelog.
- +Developing backend microservices for a payment-related invoice processing system using Java 21, Spring Boot 3.5, Spring WebFlux, and PostgreSQL.
- +Built event-driven Kafka consumers handling multiple event types with header-based routing, DLQ fan-out, and structured error recovery.
- +Implemented distributed ShedLock batch schedulers for timed invoice submission workflows, with partial-failure handling and audit logging.
- +Designed dual-chain Spring Security: static Bearer-token auth for internal service-to-service calls and Keycloak OAuth2 JWT for external consumers.
- +Built a Testcontainers-based integration testing framework with a reusable base class (real PostgreSQL, WebTestClient, FK-safe teardown) — raising the JaCoCo instruction coverage gate to 75%.
- +Modernised Gradle build: Boot BOM as platform(), separate unit/integration test tasks, Allure 2.39 + JaCoCo Cobertura wired into GitLab CI.
- +Integrated Tencent Cloud COS for cloud object storage and built external API clients for downstream services using Spring WebClient.
- +Collaborating with product, QA, and cross-functional teams to deliver payment-related backend features.
Owned services
Production-grade systems built with performance and reliability as first principles. Each card is a service this engineer designed and shipped end-to-end.
Production-shaped real-time chat with JWT/RBAC, S3-backed file sharing with antivirus scanning, transactional Kafka outbox for audit, and per-conversation ordering. Sync delivery and async fan-out fail independently.
Layered Spring Boot service for users, catalog, carts, and orders with Stripe payments, robust validation, standardised error handling, and full Swagger docs. Pragmatic foundation for an e-commerce MVP.
Production-grade REST API for tracking job applications, interviews, notes, and reminders. Spring Boot 4, Java 25, Spring Modulith, Redis caching, Flyway migrations (41 versions), AI CV tailoring via Groq, WebAuthn passkeys, TOTP 2FA, Pro tier billing with Lemon Squeezy webhooks, and full OpenAPI codegen for the companion Next.js frontend.
Full-stack companion frontend for the interview-tracker API. App Router with server-side prefetch + HydrationBoundary, drag-and-drop Kanban, recharts analytics, AI JD analysis, cover-letter generation, CSV/JSON bulk import, PWA install prompt, TOTP + passkey login flows, Playwright smoke tests, and a Pro paywall wired to the 402-response pattern.
Spring Boot reactive backend for an LLM-powered knowledge assistant: retrieves and reasons over indexed engineering docs, code repos, APIs, and production systems. Supports semantic + hybrid search, multi-provider LLM routing (Anthropic, OpenAI, Ollama), ingestion pipelines (GitHub, GitLab, Confluence, web), Neo4j knowledge graphs, and JWT+OAuth2 auth with email-password fallback.
Full Next.js 16 App Router frontend for the EKA knowledge assistant. Features LLM chat with SSE streaming, hybrid code search, ingestion source management, interactive Neo4j knowledge graph, usage analytics, observability dashboards, admin user management, and email+OAuth2 auth. Radix UI primitives, TanStack Query server state, Zustand client state, Tailwind v4 theming.
Live telemetry
Pulled live from GitHub and LeetCode by an edge route handler this portfolio ships. Cached at the edge for 6 hours; falls back gracefully on rate-limit.
Topology
System diagrams for the services above. Switch modes to trace a request, or to see what happens when things break.
Router Service
API gateway · circuit breaker · dynamic LB · 10K+ RPS
Five-tier architecture. Single ingress, regex-matched routing, hand-rolled circuit breaker per route, 3 pluggable LB strategies, and a backend pool of stateless replicas. Observability via Spring Actuator + Prometheus + a WS dashboard for live tail.
tip: hover any node for details · use Sequence to trace a single request · Failure mode shows what gives way first.
Page on-call
Open to senior backend roles, system design discussions, or interesting technical collaborations. The on-call engineer is currently me.
Currently serving notice. Looking for Senior / Staff backend roles — Java, Spring Boot, Kafka, React, distributed systems. Open to remote or Pune / Bengaluru.
- ≤ 24hemaillekh.nith@gmail.com
- best-effortgithubgithub.com/lekhrocks
- ≤ 48hlinkedinlinkedin.com/in/lekhrajkumar
- biz hourslocationPune, IN · UTC+5:30