Page 600 - (ISC)² CISSP Certified Information Systems Security Professional Official Study Guide

to expand or contract based on need. In relation to virtualization, host
elasticity means additional hardware hosts can be booted when

needed and then used to distribute the workload of the virtualized
services over the newly available capacity. As the workload becomes
smaller, you can pull virtualized services off unneeded hardware so it
can be shut down to conserve electricity and reduce heat.

Some of the concepts in cloud computing are listed here:

Platform as a service Platform as a service (PaaS) is the concept of
providing a computing platform and software solution stack as a
virtual or cloud-based service. Essentially, this type of cloud solution

provides all the aspects of a platform (that is, the operating system and
complete solution package). The primary attraction of PaaS is the
avoidance of having to purchase and maintain high-end hardware and
software locally.

Software as a service Software as a service (SaaS) is a derivative of
PaaS. SaaS provides on-demand online access to specific software

applications or suites without the need for local installation. In many
cases, there are few local hardware and OS limitations. SaaS can be
implemented as a subscription service (for example, Microsoft Office
365), a pay-as-you-go service, or a free service (for example, Google
Docs).

Infrastructure as a service Infrastructure as a service (IaaS)
takes the PaaS model yet another step forward and provides not just

on-demand operating solutions but complete outsourcing options.
This can include utility or metered computing services, administrative
task automation, dynamic scaling, virtualization services, policy
implementation and management services, and managed/filtered
internet connectivity. Ultimately, IaaS allows an enterprise to scale up
new software or data-based services/solutions through cloud systems

quickly and without having to install massive hardware locally.

There are many other “X as a service” offerings available in the
marketplace, each with its own potential vulnerabilities and
advantages. Different cloud computing companies may define or label
their services differently than others. Thus, it is important to carefully
compare and contrast providers with what features and options are