Many applications constructed as Autonomous Decentralized Systems require high dependability, often leading to the use of distributed architectures and their associated fault-tolerance techniques. Consul is a system designed to support the use of such techniques in the construction of fault-tolerant, distributed systems structured according to the state machine approach. Here, the way in which modularity has been used in the design and implementation of Consul is described. Our approach to this issue makes it easy to configure a system customized to the needs of a specific application, as well as facilitating the development of the individual components that make up Consul. August 3, 1992 Department of Computer Science The University of Arizona Tucson, AZ 85721 1 Current address: Dept. of Computer Science and Engineering, University of California San Diego, La Jolla, CA 92093, USA 1 Introduction Distributed computer systems, in which multiple machines are connected by a communicati...