Extended Membership Problem for Open Groups: Specification and Solution

Abstract. A particular case of open group is that of a large-scale system where an unbounded and dynamically changing set of client nodes continuously connect and disconnect from a reduced and stable group of servers. We propose an extended specification of the membership problem, that takes into account the different consistency properties that both types of nodes require from the membership information in such a scenario. The specification is completely independent of any group communication layer, assuming only the presence of a local failure detector at each node. We also describe a membership service that satisfies the specification and sketch a proof for its properties