Automated hierarchical service level agreements

Abstract

The present dissertation concerns the area of Service Computing. More specifically, it contributes to the topic of enabling IT service stacks with dependability, such that they can be used even further in pragmatic business environments and applications. The instrument used for this purpose is a Service Level Agreement (SLA). The main focus is on SLA Hierarchies, which reflect corresponding Service Hierarchies. SLAs may be established manually, or automatically among software agents; it is mainly the latter case that is considered here.

The thesis contributes by means of a formal problem definition for the construction of SLA hierarchies using a translation process, a management architecture, a formal model for defining penalties and a representation that facilitates the processing of SLAs. Using these tools, it is shown that automated SLA management in hierarchical setups is possible, through an application to Multi-Domain Infrastructure-as-a-Service. Within this specific technical area, different SLA-based resource capacity planning approaches are examined via simulation -- both for online and offline planning. The former case concerns normal runtime operations, and the thesis examines two greedy algorithms with regard to their energy-savings efficiency and their performance. In the latter case, a resource-scarce environment is simulated with the purpose of minimizing penalties from already established SLAs. This is achieved via formally-defined combinatorial models, which are solved and compared to two greedy algorithms.