Consul Home Page

The University of Arizona, Computer Science Department
Research Projects



The Consul System


Overview Consul involved developing new techniques for designing and implementing fundamental communication services for fault-tolerant distributed programs. Our research here concentrated on communication services such as atomic multicast and membership, which have become widely recognized as fundamental building blocks for fault-tolerant distributed systems. The initial effort resulted in Consul, a modular communication substrate designed to support the state machine approach to implementing replicated processing. The core protocol in Consul is Psync, an atomic multicast protocol implementing consistent causal ordering of messages across all group members based on a context graph abstraction. Additional protocols include membership, which maintains consistent information about which sites are functioning and which have failed; total ordering, which converts the causal message ordering into a total order; and recovery, which supports the reestablishment of the application state using message replay. A prototype of Consul was constructed using the x-kernel system for building network subsystems on an experimental network of Sun-3 workstations. In Consul, each piece of the system (Psync, membership, total ordering, recovery) is implemented as a separate protocol object that communicates with other objects on the same machine and peers elsewhere using facilities provided by the x-kernel.

More recent research in this area, in particular the Coyote and Cactus projects, has been concentrating on expanding this model to support more fine-grained composition of protocol objects. In Consul, the protocol objects are relatively heavyweight objects implementing a fixed combination of properties. Moreover, because the x-kernel and similar systems are designed for building protocol stacks for traditional network protocols, objects can only be composed hierarchically and can only communicate via messages or control operations. Extending this model to include fine-grain objects simplifies the communication between objects in complicated services, as well as gives the system builder more control over precisely which properties are implemented by the communication system.
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Consul was supported by the Office of Naval Research (ONR).
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http://www.cs.arizona.edu/ftol/consul/index.html
Last updated March 2, 1998
Richard D. Schlichting (rick@cs.arizona.edu)