The process group approach to reliable distributed computing

The difficulty of developing reliable distributed softwme is an impediment to applying distributed computing technology in many settings. Expeti _ with the Isis system suggests that a structured approach based on virtually synchronous _ groups yields systems that are substantially easier to develop, exploit sophisticated forms of cooperative computation, and achieve high reliability. This paper reviews six years of resemr,.hon Isis, describing the model, its impl_nentation challenges, and the types of applicatiom to which Isis has been appfied. 1 In oducfion One might expect the reliability of a distributed system to follow directly from the reliability of its con-stituents, but this is not always the case. The mechanisms used to structure a distributed system and to implement cooperation between components play a vital role in determining how reliable the system will be. Many contemporary distributed operating systems have placed emphasis on communication performance, overlooking the need for tools to integrate components into a reliable whole. The communication primitives supported give generally reliable behavior, but exhibit problematic semantics when transient failures or system configuration changes occur. The resulting building blocks are, therefore, unsuitable for facilitating the construction of systems where reliability is impo/tant. This paper reviews six years of research on Isis, a syg_,,m that provides tools _ support the construction of reliable distributed software. The thesis underlying l._lS is that development of reliable distributed software can be simplified using process groups and group programming too/_. This paper motivates the approach taken, surveys the system, and discusses our experience with real applications.