Zeynal Calis

Designed and implemented scalable front-end web applications using React and modern JavaScript, enhancing user experience and performance in healthcare portals. Led back-end development leveraging Python and microservices to create secure REST APIs for claims processing, improving data retrieval speeds by over 30%. Collaborated with cross-functional, remote teams using Kanban to deliver iterative improvements aligned with business objectives. Defined scalable cloud architecture with AWS for high availability and fault tolerance; established rigorous QA processes including unit, integration, and end-to-end testing with Jest. Optimized cloud resources with serverless components (AWS Lambda) to reduce costs and increase scalability. Mentored junior developers, and refactored legacy Angular components to React, achieving 25% faster load times and improved accessibility.

Led modernization of a legacy estate management system by migrating to a scalable architecture with NestJS, PostgreSQL, and GraphQL; refactored core backend into modular, domain-driven structures aligned with Clean Architecture using monorepos (Nx). Built automated workflows for estate handling with event-driven architecture using AWS SQS, Lambda, and Trigger.dev; designed resilient task pipelines with retries and deduplication; developed internal tools with Retool; enhanced observability with CloudWatch and custom dashboards; provisioned infrastructure with Terraform and managed serverless deployments across AWS; strengthened authentication with OAuth2 and JWT; conducted code reviews and mentored teams on backend and cloud patterns; contributed to DevOps best practices. Initiated cross-functional collaboration with product, design, and operations to deliver scalable backend solutions.

Developed dynamic React applications with Redux for data visualization dashboards in marketplace environments. Implemented back-end services using Python and Node.js, integrating with AWS services (S3, EC2, RDS) to support scalable microservices. Led cloud infrastructure management and CI/CD pipelines, improving deployment frequency and reducing downtime. Worked in a fully remote Kanban-driven team to deliver features rapidly while maintaining high code quality. Contributed to architecture decisions focusing on scalability, security, and performance. Integrated third-party APIs and internal services for seamless data flow; conducted code reviews and enforced best practices in JavaScript, React, and Python. Implemented OAuth2 and JWT authentication to safeguard user data. Facilitated cross-team communication and English-language documentation to align stakeholders.