A Cacheonix developer is responsible for designing, implementing, and maintaining Cacheonix, an open-source Java caching system. They work on enhancing the system's performance by reducing the database load and making the system more scalable. They also debug and fix issues, ensuring the system runs smoothly and efficiently. Additionally, they contribute to the development of new features and improvements, often collaborating with other developers. They also document their work, so other developers can understand the system's architecture and functionality. Lastly, they might participate in the open-source community, sharing their knowledge and learning from others.