- Designed and implemented a microservice architecture (auth, user, order, payment, API gateway) using Java 17/21 and Spring Boot 3, with a clear layered structure (controller/service/repository/dto/exception) to keep the codebase maintainable and testable. - Developed REST APIs for user, order and payment flows with Spring Web/MVC, request validation and centralized error handling; followed REST conventions and kept controllers thin by moving business logic into services. - Implemented authentication and authorization with JWT and Spring Security; configured Spring Cloud Gateway (WebFlux) as a single entry point to validate tokens and route requests to backend services. - Built and integrated data and messaging layers: PostgreSQL (Spring Data JPA), MongoDB (Spring Data), Redis (caching), and Kafka (async events); maintained schema evolution with Liquibase for both SQL and MongoDB. - Implemented a continuous integration and deployment workflow with GitHub Actions: build, run tests, static analysis, and Docker image build; prepared deployment artifacts for running services in Kubernetes. - Configured containerization and Kubernetes deployment: wrote Dockerfiles and docker-compose for local runs; created Deployment, Service, and Ingress manifests so gateway, order and payment services run in a K8s cluster. - Implemented unit and integration tests (JUnit, Mockito, Spring Boot Test, Testcontainers, WireMock) to cover critical paths and integration with PostgreSQL, MongoDB, Kafka and Redis in containerized test environments