Rosen N. - Senior Full Stack Software Engineer

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Stara Zagora, Bulgaria

Experience

Jan 2023 - Jul 2025

2 years 7 months

Germany

Senior Full Stack Software Engineer

Zalando SE

Engineered high-performance microservices in Node.js (NestJS) and Python (FastAPI) with RabbitMQ for efficient inter-service communication.
Integrated AI-powered features using OpenAI, including intelligent auto-suggestions, content summarization, and user query understanding, enhancing UX and reducing manual input by 40%.
Developed AI agent workflows with LangChain, integrating custom retrieval pipelines and tool chaining to enable multi-step reasoning, document Q&A, and process automation, improving decision accuracy and reducing manual research time.
Built and deployed GraphQL APIs with Apollo Server (Node.js) and Graphene (Python), integrated with Next.js via Apollo Client for optimized AI-enhanced UX.
Designed an authentication microservice with JWT, SSO, and 2FA (Email OTP), deployed on AWS Lambda with AWS CDK for scalable security.
Architected real-time WebSocket infrastructure with Node.js and Redis Pub/Sub, handling thousands of concurrent connections.
Built a component-driven frontend using React 18, Redux Toolkit, TailwindCSS, and TypeScript with SSR, SSG, and ISR for SEO and performance.
Streamlined CI/CD pipelines to accelerate delivery of secure, production-grade features without service disruption.
Wrote comprehensive unit and integration tests using Jest and React Testing Library, achieving 80%+ test coverage and significantly improving UI reliability.
Defined AWS infrastructure with Terraform and orchestrated deployments with Docker & Kubernetes, reducing release cycles.
Mentored junior developers and conducted code reviews, elevating team performance by 30% while maintaining high-quality documentation with Swagger/OpenAPI.

Nov 2019 - Oct 2022

3 years

Germany

Senior Full Stack Engineer

Doctolib

Migrated a legacy monolith into a modular, cloud-native microservices architecture, applying patterns like Strangler, CQRS, API Gateway, and Saga to ensure reliable service communication and robust transaction handling.
Designed and implemented full-stack SaaS features with React/Next.js (SSR/SSG) on the frontend and modern Python/TypeScript services (Django REST Framework, NestJS) on the backend, deployed via GCP Cloud Run with Firestore for real-time sync.
Built and scaled backend services with PostgreSQL and Redis (BullMQ) to support event-driven workflows and background processing.
Automated CI/CD pipelines with Jenkins, GitLab CI, and Kubernetes, enabling faster, safer releases across AWS and GCP environments.
Used infrastructure as code (AWS CDK, CloudFormation, Terraform) to standardize deployments, cutting setup time and reducing infra drift.
optimized async processing pipelines with SQS/SNS and caching strategies to reduce cold starts and improve throughput.
Partnered with product and design teams to deliver user-facing features under tight deadlines, ensuring high quality with strong testing practices and CI/CD automation.

Oct 2017 - Sep 2019

2 years

Netherlands

Full Stack Developer

Framer

Delivered React + Django applications for internal dashboards, client portals, and e-commerce integrations, ensuring scalable, responsive front-ends and reliable back-end systems on PostgreSQL.
Built and optimized RESTful APIs using Django ORM and PostgreSQL, implemented query indexing and batch retrieval to improve performance by up to 50% for large dataset handling.
Enhanced UX and frontend performance, implemented code-splitting, lazy loading, and asset optimization in React to reduce page load times.
Implemented Elasticsearch and MongoDB indexes to improve search and enable real-time reporting.
Automated CI/CD pipelines using Jenkins and Docker-based deployments; created infrastructure-as-code scripts for repeatable, reliable deployments.
Collaborated across teams, coordinated with designers, product owners, and QA to deliver projects on time and within scope while maintaining high code quality and test coverage.

Jul 2015 - Jul 2017

2 years 1 month

Bulgaria

Junior Software Developer

Droxic

Contributed to the development of web applications by building responsive UIs using HTML, CSS, and JavaScript, and gradually transitioned into React for building reusable components in single-page applications.
Collaborated with designers and senior engineers to convert Figma/Sketch mockups into clean, accessible, and mobile-friendly frontends, following web standards and UX best practices.
Assisted in backend development using Python, implementing data processing logic and improving system performance through object-oriented design, SOLID principles, and efficient data structures.
Developed and maintained Node.js services with Express and REST APIs, integrating with MongoDB and third-party APIs to support real-time features and improve backend scalability.
Gained early exposure to AWS and GCP, using services such as EC2, S3, and Cloud Functions to deploy and test development builds in cloud environments.

Summary

Results-driven Senior Full-Stack Engineer with 10+ years of experience designing and delivering scalable, high-performance, and cloud-native applications.

Recognized for building systems that reduce operational costs, improve performance, and drive measurable business impact.

Passionate about clean architecture, developer productivity, and leading cross-functional teams to deliver production-ready software.