Infrastructure-as-a-Service clouds are rapidly evolving into market-like environments that offer a wide range of server contracts. Amazon EC2's spot market is the clearest example of this trend: it operates over 5000 markets globally where users can rent servers for a variable price. To exploit spot instances, while mitigating the risk of price spikes and revocations, many researchers and startups have developed techniques for modeling and predicting prices to optimize spot server selection.

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... ever, prior approaches focus largely on predicting individual server prices, which is akin to predicting the price of a single stock. We argue that researchers should instead focus on "index-based" modeling and prediction that aggregates prices from many markets in each region and availability zone. We show that, for applications flexible enough to select and "trade" servers globally, making decisions based on broader indices lowers costs and improves availability compared to index-agnostic policies.