Current cloud computing infrastructures and their management are highly centralized, and therefore they suffer from limitations in terms of network latency, energy consumption, and possible legal restrictions. Decentralizing the Cloud has been recently proposed as an alternative. However, the efficient management of a geographically dispersed platform brings new challenges related to service localization, network utilization and locality-awareness. We here consider a cloud topology composed of

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... any small datacenters geographically dispersed within the backbone network. In this paper, we present the design, development and experimental validation of Koala, a novel overlay network that specifically targets such a geographically distributed cloud platform. The three key characteristics of Koala are laziness, latencyawareness and topology-awareness. By using application traffic, Koala maintains the overlay lazily while it takes locality into account in each routing decision. Although Koala's performance depends on application traffic, through simulation experiments we show that for a uniformly distributed traffic, Koala delivers similar routing complexity and reduced latency compared to a traditional proactive protocol, such as Chord. Additionally, we show that despite its passive maintenance, Koala can appropriately deal with churn by keeping the number of routing failures low, without significantly degrading the routing performance. Finally, we show how such an overlay adapts to a decentralized cloud composed of multiple small datacenters.