Elasticity in Service Level Agreements

Elasticity has been identified as one of the key features of delivering IT services over the internet. Major definitions of cloud computing consider elasticity as an essential property of cloud services, and as one of the main reasons to use cloud infrastructures. However, customers expect and hope for the elasticity promise without having any guarantee or contractual agreement. While elasticity has mostly been considered on qualitative terms, there have been recent efforts in quantifying elasticity and thus enabling the measurement of elasticity. Based on new approaches of defining elasticity, it becomes possible to specify precise and meaningful elasticity guarantees, which is advantageous for both consumers and providers of cloud services. This work contributes to the ongoing elasticity research by including elasticity terms into service level agreements (SLAs). This is achieved by restricting the validity of service level objectives with respect to the available elasticity. The approach is explained in detail and its advantages and consequences for service providers and consumers are discussed.