FirecREST v2: lessons learned from redesigning an API for scalable HPC resource access

Introducing FirecREST v2, the next generation of our open-source RESTful API for programmatic access to HPC resources. FirecREST v2 delivers a 100x performance improvement over its predecessor. This paper explores the lessons learned from redesigning FirecREST from the ground up, with a focus on integrating enhanced security and high throughput as core requirements. We provide a detailed account of our systematic performance testing methodology, highlighting common bottlenecks in proxy-based APIs with intensive I/O operations. Key design and architectural changes that enabled these performance gains are presented. Finally, we demonstrate the impact of these improvements, supported by independent peer validation, and discuss opportunities for further improvements.