A federated cloud storage setup which integrates and utilizes storage resources from multiple cloud storage providers has become an increasingly popular and attractive paradigm for the persistence tier in cloud-based applications (e.g., SaaS applications, IoT applications, etc). However, federated cloud storage setups are prone to run-time dynamicity: many dynamic properties impact the way such a setup is governed and evolved over time, e.g., storage providers enter or leave the market; QoS metrics and SLA guarantees may change over time; etc. In general, existing federated cloud systems are oblivious to dynamic properties of the underlying operational environment, resulting in both sub-optimal data management decisions and costly SLA violations. Additionally, due to the sheer complexity of cloud-based applications coupled with the heterogeneous and volatile nature of federated cloud setups, the complexity of building, maintaining, and expending such applications increases dramatically and therefore managing them manually is no longer simply an option. To address these concerns, we present SCOPE, a policy-based and autonomic middleware that provides self-adaptiveness for data management in federated clouds. We have validated SCOPE in the context of a realistic SaaS application, performed an extensive functional validation, and conducted a thorough experimental evaluation. The evaluation results demonstrate (i) the ability of the middleware to perform data management decisions that take into account the run-time dynamicity (i.e., dynamic properties) of a federated cloud storage setup to meet the promised SLAs, and (ii) the self-adaptive behavior of SCOPE without the need for operator intervention. In addition, our in-depth performance evaluation results indicate that the benefits are achieved with acceptable performance overhead, and as such highlight the applicability of the proposed middleware for real-world application cases.

中文翻译：

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范围：用于联合云的自适应和基于策略的数据管理中间件

集成和利用来自多个云存储提供商的存储资源的联合云存储设置已成为基于云的应用程序（例如，SaaS应用程序，IoT应用程序等）中的持久层越来越流行和有吸引力的范例。但是，联邦云存储设置倾向于具有运行时动态性：许多动态属性会影响这种设置随时间的支配和演变方式，例如存储提供商进入或退出市场；QoS指标和SLA保证可能会随着时间而变化；通常，现有的联合云系统忽略了底层操作环境的动态属性，从而导致次优的数据管理决策和代价高昂的SLA违规。另外，由于基于云的应用程序极其复杂，加上联合云设置的异构性和易变性，因此构建，维护和扩展此类应用程序的复杂性急剧增加，因此手动管理它们已不再是一种选择。为了解决这些问题，我们介绍了SCOPE，这是一种基于策略的自主中间件，可为联合云中的数据管理提供自适应性。我们已经在实际的SaaS应用程序中验证了SCOPE，进行了广泛的功能验证，并进行了全面的实验评估。评估结果证明（i）中间件执行考虑到运行时动态性（即，动态属性）来满足承诺的SLA，以及（ii）SCOPE的自适应行为而无需操作员干预。此外，我们的深入性能评估结果表明，以可接受的性能开销实现了这些好处，因此突显了所建议的中间件在实际应用案例中的适用性。