Cluster rolling upgrade using multiple version support

This paper presents a design that supports rolling up-grades of a cluster operating system. The mechanism supports multiple, concurrently active versions of cluster operating system software components. This approach supports complex software changes, where the relationships between new and old components are not just "1-1", but also can be "many-to-one" and "one-to-many". The software components are typically organized as objects, and interactions follow a client-server model.