A Distributed Presence Service over Epidemic Multicast

In a dynamic distributed system with a very large number of nodes, such as a cloud, it issometimes useful to discover the nodes that are up in the system at a given time. The number of those nodes changes continually along the operation time, as some nodes crash and some join the system. In this paper we introduce a presence service that was implemented over a gossip structure using an epidemic multicast protocol. Unlike other common presence services, our service is fully distributed. Due to epidemic dissemination and inherent redundancy provided by the multicast protocol, the service is resilient against message loss and link crashes. In a scenario we developed to evaluate the efficiency and scalability of our presence service, we show how presence notifications propagate to reach all nodes in the group and we also show how adjustments for the gossip configuration can benefit the efficiency and resilience of the notification dissemination. The results of the experimental evaluation show that following a distributed approach over epidemic communication leads to a resilient and scalable presence service. Key words: Presence service, epidemic protocols, resilience, fault tolerance, clouds.