A Cinder developer works on OpenStack's Cinder project, which provides block storage services for cloud infrastructure. Their duties include designing, coding, and testing the software to ensure it efficiently manages and provisions persistent block storage to virtual machines. They often collaborate with other developers, troubleshoot issues, and contribute to the project's open-source community by providing solutions, enhancements, and bug fixes. They also ensure the software's compatibility with various storage systems and platforms. Additionally, they need to stay updated with the latest developments in cloud computing and storage technologies.