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lekhrajkumar

Backend Software Engineer. 5+ years owning high-throughput distributed systems in payments & SaaS. Hands-on with React when the UI is the bottleneck.

healthy · serving trafficopen to senior backend rolesap-south-1·edge
Lekhraj Kumar
owner
Lekhraj Kumar
role
Sr. SWE · CP Axtra
location
Pune, India · remote-friendly
tags
javaspring-bootkafkamicroservicesawsreactdistributed-systems
RPS sustained
10K+
router-service
p99 latency
<20ms
router-service
Kafka throughput
billing pipeline
SLA achieved
99.9%
appdirect prod
LeetCode solved
729+
@lekh_nith
Years shipping
5+
since 2020
actionsprimary & links

Note: this portfolio ships live edge endpoints — /api/health and /api/stats. Open them.

recent activity
  • deploy
    appdirect/billing
    Migrated RabbitMQ → Kafka (4× throughput)
    2024
  • ship
    router-service
    10K+ RPS sustained, p99 < 20ms
    2025
  • publish
    case-studies/router-service
    Wrote up tradeoffs and outcome
    2026
01.owner

Owner

Who runs this service. Bio, education, signals, and the engineering principle I keep coming back to.

summary.md

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.

current
CP Axtra — Sr. SWE
since
Jun 2026
location
Remote
open to
Senior · Staff
leetcode
729+
problems solved
@lekh_nith · Top 10%
education
NIT Hamirpur
NIT Hamirpur 8.65 GPA

B.Tech + M.Tech · Electronics & Communication

2015 – 2020

location
Pune, IN
UTC+5:30 · remote-friendly

Great systems aren't just fast — they're observable, resilient, and maintainable. I build for the 3am incident, not just the happy path.

— principle
currently
  • Building Invoice Management System at CP Axtra
  • Writing case studies for shipped systems
  • Senior Software Engineer · CP Axtra
02.stack

Stack & tooling

9 groups · 49 entries

What this service runs on. Primary tags marked with a leading dot.

languages5
  • Java
  • Golang
  • JavaScript
  • TypeScript
  • SQL
backend & APIs8
  • Spring Boot
  • Spring Security
  • Hibernate / JPA
  • RESTful APIs
  • GraphQL
  • WebSockets
  • OAuth2
  • Spring AI
AI & LLMs7
  • OpenAI / GPT
  • Anthropic / Claude
  • Cohere
  • Groq
  • Ollama
  • RAG
  • Prompt Engineering
architecture5
  • Microservices
  • Event-Driven
  • Domain-Driven Design
  • System Design (HLD/LLD)
  • SaaS Platforms
messaging & streaming2
  • Apache Kafka
  • RabbitMQ
data & caching4
  • PostgreSQL
  • MySQL
  • MongoDB
  • Redis
cloud & devops6
  • AWS
  • Docker
  • Kubernetes
  • Helm
  • GitHub Actions
  • Jenkins
observability6
  • Prometheus
  • Datadog APM
  • Spring Actuator
  • Elasticsearch
  • Logstash
  • Centralized Logging
testing & quality6
  • JUnit
  • Mockito
  • Integration
  • Contract
  • TDD
  • CI/CD Pipelines
runtime characteristicsproduction patterns
JVM tuning
Memory · GC · thread pools
Resilience patterns
Circuit-break · retry · rate-limit
Observability
Prometheus · Actuator · Datadog
Load testing
10K+ RPS · 1M+ requests
03.deployments

Deployment history

3 deploys · main

Where this engineer has shipped. Newest deploy first. Click a row to expand the changelog.

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.
Java 21Spring Boot 3.5WebFluxKafkaPostgreSQLTestcontainersShedLockKeycloakTencent CloudGitLab CIDocker
04.services

Owned services

7 services · all healthy

Production-grade systems built with performance and reliability as first principles. Each card is a service this engineer designed and shipped end-to-end.

router-service

stable

High-Performance request router & load balancer

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.

sustained
10K+ RPS
p99
<20ms
memory
210MB
Java 21Spring Boot 3.5DockerPrometheusWebSockets

realtime-chat

stable

WebSocket chat backend with Kafka audit pipeline

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.

ack p99
<80ms
audit lag
<2s p95
ordering
per-conv
Java 21Spring BootGraphQLKafkaWebSocketsAWS S3

ecommerce-backend

active

RESTful e-commerce backend with Stripe payments

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.

payment
Stripe
schema
MySQL
docs
Swagger
Java 11Spring Boot 2.7JPAMySQLStripeSwagger

interview-tracker-api

stable

Full-featured job-search backend — Spring Boot 4 / Java 25

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.

migrations
41 versions
modules
9 domain
coverage
≥55% lines
Java 25Spring Boot 4Spring ModulithPostgreSQLRedisFlywaySpring AIWebAuthnJWTDocker

interview-tracker-ui

stable

Next.js 14 App Router frontend with SSR, React Query, and Pro paywall

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.

pages
15+ routes
e2e
Playwright
SSR
HydrationBoundary
Next.js 14React 18TypeScriptTailwind CSSReact QueryZodPlaywrightPWA

eka-backend

stable

AI-powered engineering knowledge assistant — API backend

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.

tests
60+ unit
migrations
8 versions
audit
91 fix items
Java 21Spring Boot 3.4Spring WebFluxSpring AIPostgreSQL+pgvectorApache KafkaRedisNeo4jOpenAIAnthropicCohereDocker

eka-frontend

stable

EKA chat UI & analytics dashboard — Next.js App Router

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.

routes
12 pages
real-time
SSE chat
auth
3 channels
Next.js 16React 19TypeScriptTailwind CSS v4TanStack Query 5Zustand 5SSERadix UIRechartsreact-markdownMermaid
05.telemetry

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.

github stars
loading…
public repos
loading…
leetcode solved
729
@lekh_nith
years shipping
5
distributed systems · payments · saas
top languages on github
06.topology

Topology

5 diagrams

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

Java 21Virtual threadsCircuit breakerRate limitPrometheus
CLIENT TIERINGRESSROUTING COREBACKEND TIEROBSERVABILITYWeb client · sends HTTPS / WebSocketWebBrowserMobile client · sends HTTPS / WebSocketMobileiOS / AndroidPartner client · sends HTTPS / WebSocketPartner3rd-party APIInternal client · sends HTTPS / WebSocketInternalMicroserviceSingle ingress for all clients. TLS terminates here.API GatewayHTTPS · WS · gRPCToken-bucket rate limiter, per-IP. 1000 req/s burst, 100 r/s sustained.Rate Limitertoken bucketValidates JWT or API key. Adds tenant claim to request context.Auth MiddlewareJWT · API keyRegex-matched routing rules. ~800 LoC core, virtual-thread powered.Router Engineregex · path · headerHand-rolled per-route breaker. Trips after 3 failures in 10s window.Circuit BreakerCLOSED · OPEN · HALFRetries idempotent failures with jittered exponential backoff.Retry + Backoffexponential · jitter3 strategies pluggable per-route. Default: LeastConnections.Load BalancerRR · Random · LeastConnBackend instance on port :8081svc A:8081Backend instance on port :8082svc B:8082Backend instance on port :8083svc C:8083Backend instance on port :8084svc D:8084Backend instance on port :8085svc E:8085Scrapes /actuator/prometheus every 15s.Prometheusmetrics · alertsSpring Boot Actuator exposes /health, /info, /metrics.Actuatorhealth · infoWebSocket fan-out — live request tail used during incidents.WS Dashboardlive traffic tailStructured JSON logs shipped via Filebeat to ELK.Centralized LogELK / LokiJMeter & k6 scripts validate 10K+ RPS soak.Load testJMeter · k6
topology

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.

legend
Service
Datastore
Queue / Topic
External
Gateway / LB
Router / Decision
Primary flow
Async / event
Failure path
Dimmed (out of view)

tip: hover any node for details · use Sequence to trace a single request · Failure mode shows what gives way first.

07.on-call

Page on-call

accepting pages

Open to senior backend roles, system design discussions, or interesting technical collaborations. The on-call engineer is currently me.

availability

Currently serving notice. Looking for Senior / Staff backend roles — Java, Spring Boot, Kafka, React, distributed systems. Open to remote or Pune / Bengaluru.

POST /api/pageencrypted in transit