Infrastructure-as-a-Service (IaaS) provides the highest level of flexibility and customization among cloud service models. In an IaaS model, the cloud provider manages the core physical infrastructure (servers, networking, storage), but the customer retains control over the operating systems, middleware, runtime, data, and applications. This extensive control allows organizations to build and configure their environments precisely to their specifications, similar to on-premises infrastructure but without the capital expenditure and physical maintenance overhead. This model is ideal for organizations with complex or unique IT requirements that cannot be met by the more abstracted PaaS or SaaS models.

B. Platform-as-a-Service (PaaS): PaaS abstracts the underlying infrastructure, including the operating system and middleware, offering less control and customization than IaaS.

C. On-premises: While offering complete control, on-premises is a traditional deployment model, not a cloud service, and thus does not answer the question as posed.

D. Software-as-a-Service (SaaS): SaaS provides the least flexibility, as the vendor manages the entire stack, including the application. Customization is typically limited to user-level configurations.

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1. Mell

P.

& Grance

T. (2011). The NIST Definition of Cloud Computing (NIST Special Publication 800-145). National Institute of Standards and Technology. Page 2

Section "Service Models". The document specifies that with IaaS

the consumer "has control over operating systems

storage

and deployed applications

" which is the broadest scope of control among the three service models.

2. Amazon Web Services. (n.d.). What is IaaS? AWS Documentation. Retrieved from https://aws.amazon.com/what-is/iaas/. The documentation states

"IaaS provides you with the highest level of flexibility and management control over your IT resources."

3. Microsoft Azure. (n.d.). What is infrastructure as a service (IaaS)? Azure Documentation. Retrieved from https://azure.microsoft.com/en-us/resources/cloud-computing-dictionary/what-is-iaas/. The documentation notes

"Of the three cloud service models

IaaS offers the most control for the business over its hardware."

4. Armbrust

M.

Fox

A.

Griffith

R.

Joseph

A. D.

Katz

R.

Konwinski

A.

... & Zaharia

M. (2009). A view of cloud computing. Communications of the ACM

53(4)

50-58. (Also available as Technical Report No. UCB/EECS-2009-28). Section 3.1 discusses how IaaS providers like Amazon EC2 offer low-level virtualized resources

which inherently provides more flexibility for users to build their own systems compared to higher-level PaaS offerings. DOI: https://doi.org/10.1145/1721654.1721672