Federated systems have recently attracted much attention because they allow loosely coupled organizations to share resources for common benefits. However, discovering resources across administrative boundaries is challenging. Despite their willingness to share resources, many organizations prefer not to export their internal resource description to unfamiliar parties. While it is highly desirable to facilitate such voluntary sharing, the system also needs to resolve resource queries in an efficient manner. Unfortunately, none of the existing resource discovery designs, either hierarchical or DHT-based, can address these two challenges in the same time. In this paper, we present the design and evaluation of ROADS, a Replication Overlay Assisted resource Discovery Service for federated systems. In ROADS, the resource owners only export summaries, which are condensed representations of their resource records. These summaries are aggregated along a hierarchy and used to direct queries to appropriate resource owners. To improve its efficiency and resiliency, ROADS replicates the summaries using server overlays that enable "shortcuts" in query forwarding. We have implemented ROADS and evaluated its performance through extensive analysis and experiments. The results show that ROADS outperforms a DHT-based design with 1-2 orders of magnitude less overhead in update messages and 50% less query forwarding time.
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