ABSTRACT
This chapter discusses analytical modeling and optimization of an elastic cloud server system. It highlights a continuous-time Markov chain (CTMC) model for an elastic multiserver system with variable size is established. The chapter describes the concept of a hybrid multiserver system, which is a mixture of a purely elastic multiserver system and a purely inelastic multiserver system, and exhibits a certain degree of elasticity. It considers the problem of optimal elasticity that is, finding the optimal degree of elasticity, such that the average cost-performance ratio is minimized for certain probability distributions of workload. Analytical study of cloud elasticity has been conducted for both horizontal scalability and vertical scalability. An analytical model was developed by treating a cloud platform with horizontal scalability as a queueing system, and a CTMC model was used to precisely calculate the elasticity value of a cloud platform by using an analytical and numerical method.
