Ren worked on backend metrics infrastructure for the airbnb/kaldb repository, focusing on improving Prometheus metrics management using Java. They initially introduced a MetricsFactory to centralize and standardize metrics exposure, aiming to simplify meter instantiation and unify tag management across the codebase. After evaluating the impact, Ren and the team decided to roll back this approach, opting instead for direct PrometheusMeterRegistry initialization within the Astra class to maintain production stability and avoid configuration drift. Their work laid the foundation for future scalable instrumentation, with clear documentation and traceability to support ongoing metrics monitoring and refactoring efforts in a microservices environment.