Architectural Support for Extensibility and Autonomy in Wide-Area Distributed Object Systems

middleware, site autonomy. The Legion system defines a software architecture designed to support metacomputing, the use of large collections of heterogeneous computing resources distributed across local- and wide-area networks as a single, seamless virtual machine. Metasystems software must be extensible because no single system can meet all of the diverse, often conflicting, requirements of the entire present and future user community, nor can a system constructed today take best advantage of unanticipated future hardware advances. Metasystems software must also support complete site autonomy, as resource owners will not turn control of their resources (hosts, databases, devices, etc.) over to a dictatorial system. Legion is a metasystem designed to meet the challenges of managing and exploiting wide-area systems. The Legion virtual machine provides secure shared object and shared name spaces, application adjustable fault-tolerance, improved response time, and greater throughput. Legion tackles problems not solved by existing workstation-based parallel processing tools, such as fault-tolerance, wide-area parallel processing, interoperability, heterogeneity, security, efficient scheduling, and comprehensive resource management. This paper describes the Legion run-time architecture, focussing in particular on the critical issues of extensibility and site autonomy