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Cloud computing is an innovative platform for the service provider to deliver various services such as servers, networks, storage, virtual desktop and applications to the customers. These services are based on the three fundamental service models, namely infrastructure as a service (IaaS), platform as a service (PaaS) and software as a service (SaaS) (Buyya, Yeo, Venugopal et, 2009; Durao, Carvalho, Fonseka, & Garcia, 2014). IaaS cloud provides the services in the form of virtual machines that are deployed in the datacenters (Li, Qiu, Niu et al., 2010; Li et al., 2012; Panda, & Jana, 2015; Panda, & Jana, 2016). On the other hand, users demand the services in the form of leases which basically contain the requirements of the users such as number of computing nodes, start time, deadline, duration, etc. (Nathani, Chaudhary, & Somani, 2012; Panda, & Jana, 2016; Panda, & Jana, 2017). The cloud service provider (CSP), namely Amazon EC2 (Amazon EC2, 2016), Haizea (Haizea, 2016), Eucalyptus (Eucalyptus, 2016) and OpenNebula (OpenNebula, 2016) support various leases to provide the computational resources. These leases include advance reservation (AR), best effort (BE) and immediate (IM).
An AR lease (A) is a type of lease that holds a specific start time (S) and execution time (E). The tuple representation of an AR lease is as follows:A = <S, E, M> (1) where:
An AR lease is non-preemptive in nature. Therefore, M = 0. Note that the end time (EN) of an AR lease is the sum of start time and execution time. Mathematically:
EN =
S +
E(2)In this paper, we assume that an AR lease has 2-tuple (i.e., < E, M >) for the simplicity of the problem. This assumption is taken based on the assumption made in (Li et al., 2012; Panda, & Jana, 2015).
A BE lease (B) is a type of lease that needs an execution time without any specific start time. The tuple form of a BE lease is as follows:
B = <
E,
M >
(3)