Okwuibe, Liyanage, Ahmad, and Ylianttila
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and Amazon Web Service (AWS), offer several free cloud services to the public and
these services are easily accessible over the Internet.
3) Hybrid Cloud: Integrates two or more distinct cloud servers to provide cloud infrastructure for different use cases. The idea is to combine the benefits of multiple
deployment models. Cloud servers in hybrid clouds could be either a combination of
private, public or community clouds. One of the popular use cases of hybrid clouds
is in enhancing security and privacy on the cloud without incurring the overhead
costs (CAPEX) of building a private cloud. In this case, non‐critical resources like
test workloads can be hosted in the public cloud, while critical resources like user
data and workloads are hosted internally.
4) Community Cloud: A multi‐tenant model that provides cloud computing infrastructures to multiple organizations within a specific community, who share common interests or concerns. Similar to the hybrid model, the infrastructures in this model could be
placed within or outside these communities, and could be managed either internally or
by a third party. Usually, the cost of running community clouds are distributed among
selected members of the community and not each individual user [12,13].
16.2.4 Cloud Service Models
Different levels of abstraction constitute the back‐end platform of the cloud architecture. These abstractions are grouped into the different service levels, depending on
what resources are offered as a service for a given abstraction level, and this is depicted
in Figure 16.2. According to National Institute of Standards and Technology (NIST), the
three standard cloud service models are Platform as a Service (PaaS), Software as a
Service (SaaS), and Infrastructure as a Service (IaaS) [12]:
● Platform as a Service (PaaS): The transmission of platforms directly as services on the
cloud is one of the integrated set of IT solutions that cloud computing provides.
Typically, computer programs and mobile applications rely on some sort of middleware platform; this could be a set of hardware, combined with an Operating System
(OS) and some libraries. PaaS provides this platform from the cloud, hence allowing
users to develop and run applications without the overhead cost (CAPEX) of building
and maintaining separate platforms [12,14].
● Software as a Service (SaaS): Presently, SaaS is the most widely‐used cloud service
model in the IT industry. Using SaaS, a software application is hosted on the cloud
and licensed to multiple users who are normally isolated from each other. Such
services could be offered for free or on a pay‐per‐use basis over the web. Access
is usually through some lightweight client interface such as a web browser [14].
Companies such as Adobe, Google, Microsoft, Facebook and Salesforce have been
offering such services, some for decades now. Software applications such as MS
Word, Excel, Whatsapp, Skype, and several others are now offered as SaaS through
traditional web browsers.
● Infrastructure as a Service (IaaS): This is the earliest and most fundamental cloud
service model in computing. Long before the term IaaS was used, organizations were
already optimizing their large‐scale mainframe computers by allowing multiple users
simultaneous access to both hardware resources and shared CPUs. IaaS may include
virtual machines (VMs), servers, storage, network connectivity, firewalls and VLANs,
all offered to users as provisioned services.
378
and Amazon Web Service (AWS), offer several free cloud services to the public and
these services are easily accessible over the Internet.
3) Hybrid Cloud: Integrates two or more distinct cloud servers to provide cloud infrastructure for different use cases. The idea is to combine the benefits of multiple
deployment models. Cloud servers in hybrid clouds could be either a combination of
private, public or community clouds. One of the popular use cases of hybrid clouds
is in enhancing security and privacy on the cloud without incurring the overhead
costs (CAPEX) of building a private cloud. In this case, non‐critical resources like
test workloads can be hosted in the public cloud, while critical resources like user
data and workloads are hosted internally.
4) Community Cloud: A multi‐tenant model that provides cloud computing infrastructures to multiple organizations within a specific community, who share common interests or concerns. Similar to the hybrid model, the infrastructures in this model could be
placed within or outside these communities, and could be managed either internally or
by a third party. Usually, the cost of running community clouds are distributed among
selected members of the community and not each individual user [12,13].
16.2.4 Cloud Service Models
Different levels of abstraction constitute the back‐end platform of the cloud architecture. These abstractions are grouped into the different service levels, depending on
what resources are offered as a service for a given abstraction level, and this is depicted
in Figure 16.2. According to National Institute of Standards and Technology (NIST), the
three standard cloud service models are Platform as a Service (PaaS), Software as a
Service (SaaS), and Infrastructure as a Service (IaaS) [12]:
● Platform as a Service (PaaS): The transmission of platforms directly as services on the
cloud is one of the integrated set of IT solutions that cloud computing provides.
Typically, computer programs and mobile applications rely on some sort of middleware platform; this could be a set of hardware, combined with an Operating System
(OS) and some libraries. PaaS provides this platform from the cloud, hence allowing
users to develop and run applications without the overhead cost (CAPEX) of building
and maintaining separate platforms [12,14].
● Software as a Service (SaaS): Presently, SaaS is the most widely‐used cloud service
model in the IT industry. Using SaaS, a software application is hosted on the cloud
and licensed to multiple users who are normally isolated from each other. Such
services could be offered for free or on a pay‐per‐use basis over the web. Access
is usually through some lightweight client interface such as a web browser [14].
Companies such as Adobe, Google, Microsoft, Facebook and Salesforce have been
offering such services, some for decades now. Software applications such as MS
Word, Excel, Whatsapp, Skype, and several others are now offered as SaaS through
traditional web browsers.
● Infrastructure as a Service (IaaS): This is the earliest and most fundamental cloud
service model in computing. Long before the term IaaS was used, organizations were
already optimizing their large‐scale mainframe computers by allowing multiple users
simultaneous access to both hardware resources and shared CPUs. IaaS may include
virtual machines (VMs), servers, storage, network connectivity, firewalls and VLANs,
all offered to users as provisioned services.