Abstract
The focus of this position paper is the group membership problem in distributed systems. The paper describes a set of group membership protocols that were developed as part of a toolkit for building distributed/parallel applications on a cluster of workstations. The group membership service is the lowest layer in the toolkit, and it is the glue which unifies all the other layers. The group membership layer supports three protocols: Weak, strong, and hybrid membership. These protocols differ significantly in the level of consistency and the number of messages exchanged in reaching agreement. This paper briefly describes each protocol with a focus on what is new about them and where they might be used.