Karthikeyan Rajendran-Backend Java Developer | Microservices, Kafka & Cloud-Native Systems | 6.5+ Years
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Experience
Full-Stack Developer — Own Product
Self-employed
Java 21 · Spring Boot 3 · Keycloak · PostgreSQL · Docker · Nginx · GitHub Actions · DigitalOcean · React 18 · TypeScript · Plasmo
- Architected and shipped a production-ready Job Application Tracker end-to-end: REST API with 5-stage workflow, pagination, sorting, and dynamic filtering — full ownership from design to live cloud deployment on DigitalOcean.
- Implemented production-grade identity management: OAuth 2.0 / OpenID Connect / JWT / RBAC via Keycloak, applying Hexagonal Architecture and DDD principles.
- Built automated CI/CD pipeline (GitHub Actions); containerised with Docker; Nginx reverse proxy with path-based routing and SSL termination.
- Developed a Chrome Extension (Plasmo framework, Manifest V3) that auto-fills job applications directly from LinkedIn into the tracker — demonstrates full product thinking across backend API and browser client.
Software Developer
Altares Dun & Bradstreet
Java 17 · Spring Boot 3 · Spring Security · Apache Kafka · Oracle DB · MongoDB · Auth0 · Azure AD
- Led design and delivery of 10+ production RESTful microservices serving 500+ enterprise users — company profiles, credit ratings, and stakeholder data; full lifecycle from design to deployment and monitoring.
- Built and maintained event-driven architecture on Apache Kafka processing 100,000+ messages/day: fault-tolerant consumers, retry mechanisms, real-time financial data pipelines — 99.9% uptime maintained.
- Engineered enterprise SSO with Auth0 and Azure AD (OAuth 2.0 / OIDC); enforced SonarQube quality gates with <5% technical debt across all services.
- Established SLF4J/Logback structured observability; diagnosed and resolved complex production incidents in a high-availability environment.
- Mentored junior engineers in Clean Code and TDD; worked Agile/Scrum in an 8-person team; contributed to architecture discussions and code reviews, coordinating across team boundaries.
Senior Software Engineer
Lumen Technology
Java 8 · Spring Boot · Neo4j · Oracle DB · Qlik Sense
- Designed microservices for real-time processing of network performance and modem health data in high-availability telecom environments.
- Reduced fault analysis query time by ~40% through Neo4j graph modelling — demonstrating deep NoSQL performance tuning in distributed systems.
- Delivered Qlik Sense dashboards with live Oracle DB integration for 10+ clients; maintained technical debt below 5%.
Software Engineer
AT&T
Java 8 · Apache Camel · JUnit · Mockito
- Built Apache Camel integration services: XML → JSON REST transformation with intelligent routing across distributed enterprise telecom landscapes.
- Achieved 85%+ test coverage with JUnit/Mockito using a TDD approach — production incidents reduced by ~30%.
Entrepreneur & Professional Development
Self-employed
- Deliberate career transition: managed a hospitality business end-to-end (P&L, client relations, operations) while completing an intensive Java & Selenium certification programme — successfully pivoted into software development in 2019.
Industry experience
See where this freelancer has spent most of their professional time.
Experienced in Information Technology, Banking and Finance, Professional Services, Telecommunication, and Tourism.
Business area experience
See which departments and functions this freelancer has contributed to most.
Experienced in Information Technology, Product Development, Business Intelligence, Quality Assurance, Customer Service, and Finance.
Summary
Backend Java Developer with 6.5+ years designing, building, and operating production-grade microservices and event-driven, distributed systems across enterprise environments. Deep expertise in Java 17/21, Spring Boot 3, and Apache Kafka (100,000+ messages/day), with hands-on ownership of applications across the full lifecycle: design, implementation, testing, deployment, and production operation. Practitioner of Hexagonal Architecture, DDD, and TDD, with a track record of leading technical decisions and mentoring peers. Self-deployed a live production platform (job-tracker.in), containerised with Docker and automated via CI/CD — currently deepening AWS cloud-native skills to complement production DigitalOcean experience. Valid German residence permit, immediately available, no notice period.
Skills
- Frameworks: Spring Boot 3, Spring Security, Spring Cloud, Hibernate, Apache Camel, Junit, Mockito, Spring Ai (Learning)
- Architecture: Microservices, Event-Driven, Hexagonal (Ports & Adapters), Ddd, Rest Api, Distributed Systems
- Messaging: Apache Kafka (Confluent) — Topics, Partitioning, Replication, Schema Registry (Avro), Kafka Connect
- Databases: Postgresql, Oracle Db, Mysql, Mongodb, Neo4j, Redis (Sql & Nosql & Caching)
- Security: Keycloak, Oauth 2.0, Openid Connect, Jwt, Rbac, Auth0, Azure Ad
- Cloud & Devops: Aws (Ec2, S3, Rds, Iam, Lambda — In Active Development), Digitalocean (Production), Docker, Kubernetes, Github Actions, Gitlab Ci, Jenkins, Maven, Gradle, Terraform (Basic), Git
- Observability: Prometheus, Grafana, Opentelemetry (Learning), Sonarqube, Slf4j/Logback, Swagger/Openapi, Postman
- Testing: Junit 5, Mockito, Testcontainers (Learning), Tdd/Bdd — 85%+ Coverage
- Methods: Agile/Scrum, Kanban, Clean Code, Ddd, Jira, Confluence
Languages
Education
Anna University
B.Tech. · Information Technology · Chennai, India
Statistics
Experience
Global experience
Expertise
Qualifications
Profile
Frequently asked questions
Have questions? Find more information here.
Karthikeyan is based in Berlin, Germany.
Karthikeyan speaks the following languages: Hindi (Native), English (Advanced), German (Elementary).
Karthikeyan has at least 9 years of experience. During this time, Karthikeyan has worked in at least 5 different roles and for 4 different companies. The average length of individual experience is 2 years and 10 months. Note that Karthikeyan may not have shared all experience and actually has more experience.
Based on recent experience, Karthikeyan would be well-suited for roles such as: Full-Stack Developer — Own Product, Software Developer, Senior Software Engineer.
Karthikeyan's most recent position is Full-Stack Developer — Own Product at Self-employed.
In recent years, Karthikeyan has worked for Self-employed, Altares Dun & Bradstreet, and Lumen Technology.
Karthikeyan is most experienced in industries like Information Technology, Banking and Finance, and Professional Services. Karthikeyan also has some experience in Telecommunication and Tourism.
Karthikeyan is most experienced in business areas like Information Technology, Product Development, and Business Intelligence. Karthikeyan also has some experience in Quality Assurance, Customer Service, and Finance.
Karthikeyan has recently worked in industries like Banking and Finance, Professional Services, and Information Technology.
Karthikeyan has recently worked in business areas like Information Technology, Product Development, and Business Intelligence.
Karthikeyan holds a Bachelor in Information Technology from Anna University.
The availability of Karthikeyan needs to be confirmed.
Daily rate distribution
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The median daily rate is the middle value of all daily rates — half of comparable freelancers charge less, half charge more. Unlike the average, it is barely affected by outliers.
Calculated based on our freelancers’ daily rates as of 6 Sep 2026. Actual rates may vary depending on seniority level, experience, skill specialization, project complexity, and engagement length.
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