“…In the case of horizontal elasticity, CPU utilisation of the cluster is the common metric used for Reference input [44,50,51,60,61], whereas, in the case of vertical elasticity, the utilisation of individual resources is utilised as Reference input. For example, the control solutions in [55,58] rely on the use of CPU utilisation, whereas Memory consumption was focused in [53] and both components were utilised in [48]. In last, very few approaches including the control solutions proposed in [28,29,75] use both performance based (i.e., Response time) and capacity based (i.e., CPU utilisation) as Reference input.…”