Universal Cross-Cloud Communication

Integration of applications, data-centers, and programming abstractions in the cloud-of-clouds poses many challenges to system engineers. Different cloud providers offer different communication abstractions, and applications exhibit different communication patterns. By abstracting from hardware addresses and lower-level communication, the publish/subscribe paradigm seems like an adequate abstraction for supporting communication across clouds, as it supports many-to-many communication between publishers and subscribers, of which one-to-one or one-to-many can be viewed as special cases. In particular, content-based publish/subscribe (CPS) systems provide an expressive abstraction that matches well with the key-value pair model of many established cloud storage and computing systems, and decentralized overlay-based CPS implementations scale up well. However, CPS systems perform poorly at small scale, e.g., one-to-one or one-to-many communication. This holds especially for multi-send scenarios which we refer to as entourages that may range from a channel between a publisher and a single subscriber to a broadcast between a publisher and a handful of subscribers. These scenarios are common in cloud computing, where cheap hardware is exploited for parallelism (efficiency) and redundancy (fault-tolerance). With CPS, multi-send messages go over several hops before their destinations are even identified via predicate matching, resulting in increased latency, especially when destinations are located in different data-centers or zones. Topic-based publish/subscribe (TPS) systems support communication at small scale more efficiently, but still route messages over multiple hops and inversely lack the flexibility of CPS systems. In this paper, we propose CPS protocols for cloud-of-clouds communication that can dynamically identify entourages of publishers and corresponding subscribers. Our CPS protocols dynamically connect the publishers with their entourages through überlays . These überlays can transmit messages from a publisher to its corresponding subscribers with low latency. Our experiments show that our protocols make CPS abstraction viable and beneficial for many applications. We introduce a CPS system named Atmosphere that leverages out CPS protocols and illustrate how Atmosphere has allowed us to implement, with little effort, versions of the popular HDFS and ZooKeeper systems which operate efficiently across data-centers.