The Horus and Ensemble projects: accomplishments and limitations

The Horus and Ensemble efforts culminated a multi-year Cornell research program in process group communication used for fault-tolerance, security and adaptation. Our intent was to understand the degree to which a single system could offer flexibility and yet maintain high performance, to explore the integration of fault tolerance with security and real-time mechanisms, and to increase trustworthiness of our solutions by applying formal methods. Here, we summarize the accomplishments of the effort and evaluate the successes and failures of the approach.