Design of a decentralized asynchronous group membership protocol and an implementation of its communications layer

Abstract

For development of group-oriented distributed applications, a group membership protocol provides the mechanisms to dynamically adapt to changes in the membership, ensuring consistent views among all members of the group. This is achieved, by executing a distributed script, that implements a protocol, at each member to maintain a sequence of identical views, in spite of continuous changes, either voluntary or due to failure, to the membership. In asynchronous distributed environments, the protocol has to operate over a network that does not bound delivery times. This thesis presents a decentralized membership protocol, designed to operate on asynchronous environments, that organizes the members in a logical ring. The protocol assumes reliable FIFO channels, that fully interconnect all members to be available. These assumptions are later relaxed to adapt the protocol to real-world environments. Reconfigurations of the group are carried out using a two-phase algorithm. An agreement phase makes the change known to all operational members, and a commit phase integrates the change at all members, in the correct order. The protocol supports failures of one or more members, either successive or simultaneous, voluntary departures, and joining of new members. In the case of simultaneous events, the protocol ensures that they are incorporated one at a time, and following the same sequence, at all members.