IJCIS: Cooperative Information Systems

RSLA: An Approach for Managing Service Level Agreements in Cloud Environments

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Cloud providers offer services at different levels of abstraction from infrastructure to applications. The quality of Cloud services is a key determinant of the overall service level a provider offers to its customers. Service Level Agreements (SLAs) are (1) crucial for Cloud customers to ensure that promised levels of services are met, (2) an important sales instrument and (3) a differentiating factor for providers. Cloud providers and services are often selected more dynamically than in traditional IT services, and as a result, SLAs need to be set up and their monitoring implemented to match the same speed. In this context, managing SLAs is complex: different Cloud providers expose different management interfaces and SLA metrics differ from one provider to another. In this paper, we will analyze how IT service quality has been defined and managed over time, discuss how to manage SLAs in today's multi-layer, multi-sourced Cloud environments, and what to expect going forward. A particular focus will be made on the rSLA framework that enables fast setup of SLA monitoring in dynamic and heterogeneous Cloud environments. The rSLA framework is made up of three main components: the rSLA language to formally represent SLAs, the rSLA Service, which interprets the SLAs and implements the behavior specified in them, and a set of Xlets-lightweight, dynamically bound adapters to monitoring and controlling interfaces. rSLA has been tested in the context of a real pilot and found to reduce the client on-boarding process from months to weeks.