This chapter discusses the fundamental concepts of Cloud Computing including its service and deployment models. Additionally, it describes the… [600143]

Chapter 1
Cloud Computing
This chapter discusses the fundamental concepts of Cloud Computing including its service
and deployment models. Additionally, it describes the Infrastructure as a service in details.
1.1 introduction
Recently, cloud computing has emerged as new paradigm. This term was first coined by
the CEO of Google Eric Schmidt in 2006, and within a few years it becomes used all over the
world [ 1]. From the beginning, several studies [ 2] [3] [4] expect that this paradigm will make
a technological revolution in the new decade. The variety of its offered services have led to
many works. Sections bellow will discuss the concept of Cloud computing in more detail.
1.2 Definition
The cloud computing emergence as a new paradigm drew the researcher’s attention over
the past few years. Nevertheless the huge number of published paper, cloud computing’s
definition is still cloudy. Most of existing studies share some similar concepts. In 2008, Foster
et al.[ 4] defined Cloud computing as a distributed computing infrastructure characterized
by its scalability and its ability to provide users a different levels of services such as: 1)
computing infrastructure, 2) a platform for development, and 3) software. In addition, this
new paradigm offers the possibility to dynamically configure these services.
Vaquero et al [ 5] proposed their own definition based on existing ones. They defined
cloud computing infrastructure with three main features: 1) Virtualized resource that can
dynamically configured, 2) a pay per use model, and 3) an infrastructure provider that

2 Cloud Computing
offers to its users’ Service level agreements called SLA. In this paper, authors represent
virtualization of a cloud’s resources by the fact to use different kind of techniques and tips
in order to decouple the hardware architecture and the software resources from its physical
implementation [ 6]. Masdari et al [ 7] support authors and explain the virtualization features
by dividing the hardware resources into several execution environments so that we talk about
Virtual Machines (VMs). The second features addressed to cloud’s users. It consists to offer
them different cloud services that can be accessed anytime anywhere. The payment method
depending on the computing resources usage [5].
The National Institute of Standards and Technology (NIST) [ 3] define cloud computing
based on its essential aspects as:
A model for enabling convenient, on-demand network access to a shared pool
of configurable computing resources (e.g., networks, servers, storage, applica-
tions, and services) that can be rapidly provisioned and released with minimal
management effort or service provider interaction.
A recent definition by Farahnakian et al [ 8] define cloud computing as a new paradigm
that compound existing concepts and technologies, such as data centers and virtualization,
and yield them new perspective. Additionally, authors present the basic service models of
cloud computing as well as the different existing deployment models. The service models of
cloud computing can be classified into three categories: 1) Infrastructure as a Service (IaaS),
2) Platform as a Service (PaaS), and 3) Software as a Service (SaaS). In the other hand, there
is four deployment models: 1) private cloud, 2) community cloud, 3) public cloud, and 4)
hybrid cloud.
So that, Cloud computing can be referred as:
A paradigm that offers on-demand the access to a different kind of scalable
services, such as Infrastructure as a Service (IaaS), Platform as a Service (PaaS),
and Software as a Service (SaaS), and using them based on pay per use model.
1.3 Cloud computing architecture
This section present the system architecture, service models and various deployment Models
of cloud computing.

1.3 Cloud computing architecture 3
1.3.1 layered model of cloud computing
Cloud computing have gained an increasing attention in the past few years. Existing studies
divided its architecture into four major layers [ 3] : 1) the hardware layer, 2) the infrastructure
layer, 3) the platform layer, and 4) the application layer.
The hardware layer sometimes known as datacenter layer, refers to the layer that manage
the different physical resources of the cloud such as physical servers, routers, switches and
power. Typically, it is implemented in data centers that includes a huge number of servers.
These servers are organized in racks and interconnected to each other by switches or routers.
The main role of this layer is to maintain the hardware configuration, the fault tolerance, the
traffic management, the power and to cool resource management.
The infrastructure layer, sometimes known as the virtualization layer, refers to the layer that
creates a pool of storage and computing resources. This pool are generated by partitioning the
physical resources based on virtualization technologies. This layer offers users the possibility
to deploy their own applications. In the other hand, the cloud providers can easily manage
the underlying infrastructure of the service.
Figure 1.1: The business model of cloud computing

4 Cloud Computing
The platform layer which is built upon the infrastructure layer, offers developers an
integrated environment to directly design, develop and test their own cloud applications and
services. The development frameworks are usually controlled by the cloud providers. It
exists a large number of development environment such as Google App Engine that provide
an API support to easily implement and save data of web applications.
The application layer which is the top layer, consists of offering customers a various
applications over the cloud. In this layer, users select their applications according to their
needs and the cloud provider’s offers.
Figure 1 illustrates the different layered model of cloud computing as well as its corre-
sponding service model
1.3.2 Service model
Based on the previous section, cloud computing enables users to utilize its resources
including storage servers, platforms, computation power, software and applications. Existing
works [ 2] [3] [8] categorized these services into three main directions (Figure 1): 1) Infras-
tructure as a Service (IaaS), 2) Platform as a Service (PaaS), and 3) Software as a Service
(SaaS).
Infrastructure as a service (IaaS) provides fundamental computing resources to Customers
that include storage, computation capacity, load balancers, network devices and firewalls [ 9].
Typically, these resources are available over virtual machines (VM) which allows a customer
to deploy and run his own servers or network equipment [ 2] [3]. As well, the virtualization
concept, guarantees the scalability of the different resources according to user’s needs. It
exists a lots of IaaS in the literature such as Amazon EC2, AppNexus and ENKI.
Software as a Service (SaaS) offers cloud customers the ability to access and utilize
applications that are hosted by cloud providers across the internet [ 2] [10]. So that there
is no need to install and run applications on customer’s machine. A large number of SaaS
are broadly available over the cloud including the SaaS CRM provided by Salesforce.com
(2014), Google Mail and Google Docs.
Platform as a Service (PaaS) represent a development platform that support the full
Lifecycle of a software [ 2] [3]. It allows customer to develop applications and services. Ad-

1.3 Cloud computing architecture 5
ditionally, it offers a deployment and configuration management tools for cloud applications.
One typical example is the PaaS Google AppEngine.
Besides these three main categories, it exists in the literature another ones such as: Data
storage as a Service (DaaS) [ 2] which offers customers a virtualized storage on demand,
Hardware as a service (HaaS) [1] and Shared application infrastructure as a service [11].
Table 1 illustrates the characteristics of the main three cloud services (Software as a Ser-
vice, Platform as a Service and Infrastructure as a service) and present some examples as well.
Service Type Offered services Examples
Software as a Service Utilize applicationsCRM provided by Sales-
force.com, Google Docs
Platform as a ServicePlatform to develop ap-
plications and servicesGoogle AppEngine
Infrastructure as a ser-
viceComputing resources in-
cluding storage, compu-
tation capacity, load bal-
ancers, network devices
and firewallsAmazon EC2, App-
Nexus
Figure 1 : Cloud Computing services
1.3.3 Deployment Models
The various groups of cloud customers causes the existence of different cloud deployment
models. Existing studies shown three main types: public cloud, private cloud, and hybrid
cloud, where each one have some benefits as well as drawbacks.
The public cloud represent the most dominant type of cloud computing model. The cloud
service providers offers customers the access to their resources based on pay-per-use model
or subscription [ 3]. Additionally, they have the full ownership of this model including its own
policy, no initial capital investment on infrastructure and shifting of risks to infrastructure
providers [ 2]. Nevertheless, the public cloud deployment model do not offers a full control
over data, network and security settings which reduce their effectiveness. It exists a lots
of popular cloud services that support public clouds including Amazon EC2, S3, Google
AppEngine, and Force.com.

6 Cloud Computing
The private cloud which called internal clouds as well [ 3], is designed to offers its services
to a single organization. The services are usually managed by the organization and used
the existing in-house resources including its Data center [ 2]. Additionally, it take a high
degree of control over performance, reliability and data privacy to ensure the security and
trust. However, the data transfer cost to a Public Cloud is still remarkable and it require a
huge investment for the cloud infrastructure in the first stage. An example of private cloud is
an Australian bank Westpac [96these] that created its own private cloud for security reason.
The hybrid clouds is the combination of the two previous models the public cloud and
the private cloud [ 3]. It tries to address their limitations, so that ensure the security without
decreasing the flexibility. In this model, the service infrastructure runs in private cloud to
control the core activities. In the other hand, the remaining part execute in the public cloud
to offer customers flexible on-demand services.
Due to the increasing users needs of computing resource, the cloud provider with different
types (Public, private and hybrid cloud)needs a massive Data center. A report of an existing
study show that Google has more than a million servers .
1.4 Infrastructure as a service
This section studies the architecture of Infrastructure as a service model and highlights its
different issues.
1.4.1 IaaS architecture
An IaaS cloud architecture typically divided into two main components: The physical infras-
tructure and The cloud OS. The first one, encompasses servers with networks and Storage.
The second take into account the management of the physical and virtual infrastructures.
Additionally, it controls the provisioning of virtual resources depending on user’s needs. So
that customers can access to a flexible and secure execution environment that abstracts the
physical infrastructure and different interfaces for interacting with the cloud. In the other
hand, it offers local users and mostly administrators local interfaces and administrative tools
in order manage, control and monitor both virtual and physical infrastructure.

1.4 Infrastructure as a service 7
Among examples of cloud OS platform are OpenNebula (http://opennebula.org) which
focus on datacenter virtualization as Figure 2 shows, OpenStack (http://openstack.org) and
Eucalyptus (www.eucalyptus.com) which focus on public cloud features.
Figure 1.2: The main component of an IaaS cloud architecture
As figure 2 shows, the core cloud OS components is composed by the virtual machine
(VM) manager, network manager, storage manager, and information manager. These infras-
tructure drivers serves to deploy, manage, and monitor the virtualized infrastructures.
1.4.2 Issues in IaaS

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