Research challenges in managing and using Service Level Agreements

A Service Level Agreement (SLA) represents an agreement between a service user and a provider in the context of a particular service provision. SLAs con- tain Quality of Service properties that must be maintained by a provider, and as agreed between a provider and a user/client. These are generally defined as a set of Service Level Objectives (SLOs). These properties need to be measurable and must be monitored during the provision of the service that has been agreed in the SLA. The SLA must also contain a set of penalty clauses specifying what happens when service providers fail to deliver the pre-agreed quality. Hence, an SLA may be used by both a user and a provider - from a user perspective, an SLA defines what is required - often defined using non-functional attributes of service provision. From a providers perspective, an SLA may be used to support capacity planning - especially if a provider is making it's capability available to multiple users. An SLA may be used by a client and provider to manage their behaviour over time - for instance, to optimise their long running revenue (cost) or QoS attributes (such as execution time), for instance. The lifecycle of an SLA is outlined, along with various uses of SLAs to support infrastructure management. A discussion about WS-Agreement - the emerging standard for specifying SLAs - is also provided.