Resource discovery is a key issue in Grid environments, since applications are usually constructed by composing hardware and software resources that need to be found and selected. Classical approaches to Grid resource discovery, based on centralized or hierarchical approaches, do not guarantee scalability in large-scale, dynamic Grid environments. On the other hand, the Peer-to-Peer (P2P) paradigm is emerging as a convenient model to achieve scalability in distributed systems and applications. This chapter describes a protocol and an architecture that adopt a pure-decentralized P2P approach to support resource discovery in OGSA-compliant Grids. In particular, the chapter describes a modified Gnutella protocol, named Gridnut, which uses appropriate message buffering and merging techniques to make Grid Services effective as a way to exchange discovery messages in a P2P fashion. We present the design of Gridnut. and compare Gnutella and Gridnut performances under different network and load conditions. The chapter presents also an architecture for resource discovery that adopts the Gridnut approach to extend the model of the Globus Toolkit 3 information service.
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