Unit iv

UNIT - IV
CLOUD SERVICE MODELS
The National Institute of StandardsandTechnology(NIST) definesthree basicservice models,namely,
1.IaaS (Infrastructure asa Service)
2. PaaS (Platformasa Service)
3. SaaS (Software asa Service)
1.IaaS (Infrastructure as a Service):
The ability given to the infrastructure architects to deploy or run any software on the computing
resources provided by the service provider. Here, the underlying infrastructures such as compute,
network, and storage are managed by the service provider. Thus, the infrastructure architects are
exemptedfrommaintainingthe datacenterorunderlyinginfrastructure.The endusersare responsible
formanagingapplicationsthatare runningontopof the service providercloudinfrastructure.Generally,
the IaaSservicesare providedfromthe service providerclouddatacenter.The enduserscanaccessthe
services from their devices through web command line interface (CLI) or application programming
interfaces(APIs) providedbythe service providers.Some of the popularIaaSprovidersinclude Amazon
Web Services (AWS), Google Compute Engine, OpenStack, and Eucalyptus.
2. PaaS(Platform as a Service):
The ability given to developers to develop and deploy an application on the development platform
providedbythe service provider.Thus,the developersare exemptedfrommanagingthe development
platformandunderlyinginfrastructure.Here,the developers are responsible formanagingthe deployed
applicationandconfiguringthe developmentenvironment.Generally,PaaSservicesare providedbythe
service provider on an on-premise or dedicated or hosted cloud infrastructure. The developers can
access the development platform over the Internet through web CLI, web user interface (UI), and
integrateddevelopmentenvironments(IDEs).Some of the popularPaaSprovidersinclude GoogleApp
Engine, Force.com, Red Hat OpenShift, Heroku, and Engine Yard.

3. SaaS (Software as a Service):
The abilitygiventothe enduserstoaccessanapplicationoverthe Internetthatishostedandmanaged
by the service provider.Thus,the endusersare exemptedfrommanagingorcontrollinganapplication,
the development platform, and the underlyinginfrastructure.Generally, SaaS services are hosted in
service provider– managed or service provider–hosted cloud infrastructure. The end users can access
the services from any thin clients or web browsers. Some of the popular SaaS providers include
Saleforce.com, Google Apps, and Microsoft office 365.
In IaaS, the end users are responsible for maintaining the development platform and the
application running on top of the underlying infrastructure. The IaaS providers are responsible for
maintaining the underlying hardware as shown in Figure 5.2a.
In PaaS, the end usersare responsibleformanagingthe applicationthattheyhave developed.
The underlyinginfrastructure willbe maintainedbythe infrastructureproviderasshowninFigure 5.2b.
In SaaS, the end user is free from maintaining the infrastructure, development platform, and
applicationthattheyare using.All the maintenance will be carriedoutby the SaaS providersas shown
Figure 5.2c.
Cloud Deployment Models:
The NIST defines four different types of cloud deployment models, namely,
1.public cloud:
The public cloud is provided for the general public.
2. private cloud:

The private cloud is used by an organization for its multiple business units.
3.community cloud:
The community cloud is for some group of organization with the same goals.
4.hybrid cloud:
The hybrid cloud is any combination of the public, private, and community clouds.
The service delivery of cloud services through different deployment models is shown in Fig 5.3.
Infrastructure as a Service:
IaaS changes the way that the compute, storage, and networking resourcesare consumed. In
traditional data centers, the computing power is consumed by having physical access to the
infrastructure. IaaS changes the computing from a physical infrastructure to a virtual infrastructure.
IaaS providesvirtual computing,storage,andnetworkresourcesbyabstractingthe physical resources.
Technologyvirtualizationisusedtoprovide the virtual resources.All the virtual resourcesare givento
the virtual machines (VMs) that are configured by the service provider. The end users or IT architects
will use the infrastructure resources in the form of VMs as shown in Figure 5.4.

Services Provided by IaaS provider:
A typical IaaS provider may provide the flowing services as shown in Figure 5.5:
1. Compute:
Computingasa Service includesvirtual centralprocessingunits(CPUs) andvirtual mainmemoryforthe
VMs that are provisioned to the end users.
2. Storage:
IaaSprovidesback-endstorage forthe VMimages.Someof the IaaSprovidersalsoprovidethe backend
for storing files.
3. Network:

NetworkasaService (NaaS) providesvirtualnetworkingcomponentssuchasvirtual router,switch,and
bridge for the VMs.
4. Load balancers:
Load Balancing as a Service may provide load balancing capability at the infrastructure layer.
Characteristics of IaaS:
1. Web access to the resources:
The IaaSmodel enablesthe ITuserstoaccessinfrastructureresourcesovertheInternet.Whenaccessing
a huge computing power, the IT user need not get physical access to the servers. Through any web
browsers or management console, the users can access the required infrastructure.
2. Centralized management:
Even though the physical resources are distributed,the management will be from a single place. The
resources distributed across different parts can be controlled from any management console. This
ensures effective resource management and effective resource utilization.
3. Elasticity and dynamic scaling:
IaaS provideselastic serviceswhere the usage of resources can be increasedor decreasedaccording
to the requirements. The infrastructure needdependsonthe loadonthe application.Accordingtothe
load,IaaS servicescan provide the resources.The load on any applicationisdynamicand IaaS services
are capable of proving the required services dynamically.
4. Shared infrastructure:
IaaS follows a one-to-many delivery model and allows multiple IT users to share the same physical
infrastructure. The differentITuserswill be givendifferentVMs. IaaSensureshighresourceutilization.
5. Preconfigured VMs:
IaaS providers offer preconfiguredVMs with operating systems (OSs),networkconfiguration, etc. The
IT userscan selectanykindof VMs of theirchoice.The IT usersare free toconfigure VMsfromscratch.
The users can directly start using the VMs as soon as they subscribed to the services.
6. Metered services:
IaaS allowsthe ITusersto rentthe computingresourcesinsteadof buyingit.The servicesconsumedby
the IT userwill be measured,andthe userswill be chargedby the IaaS providersbased onthe amount
of usage.
Suitability of IaaS:
IaaS can be used in the following situations:
1. Unpredictable spikes in usage:
When there is a significant spike in usage of computing resources, IaaS is the best option for IT
industries.Whendemandisveryvolatile,we cannotpredictthe spikesandtroughsintermsof demand
of the infrastructure. In this situation, we cannot add or remove infrastructure immediatelyaccording
tothe demandinatraditional infrastructure.If thereisanunpredictable demandof infrastructure,then
it is recommended to use IaaS services.
2. Limited capital investment:

Newstart-upcompaniescannotinvestmore on buyinginfrastructure fortheirbusinessneeds.Andso
by using IaaS, start-up companies can reduce the capital investment on hardware.IaaS is the suitable
option for start-up companies with less capital investment on hardware.
3. Infrastructure on demand:
Some organizations may require large infrastructure for a short period of time. For this purpose, an
organization cannot afford to buy more on-premise resources. Instead, they can rent the required
infrastructure fora specificperiodof time.IaaSbestsuitsthe organizationsthatlookfor infrastructure
on demand or for a short time period.
Not Suitable Situations of IaaS:
There are some situations where IaaS may not be the best option. In followingsituations,IT
users should avoid using the IaaS:
1. When regulatory compliance does not allow off-premise hosting:
For some companies,itsregulationmaynotallow the applicationanddatato be hostedon third-party
off-premise infrastructure.
2. When usage is minimal:
When the usage is minimal and the available on-premise infrastructure itself is capable of satisfying
their needs.
3. When better performance is required:
Since the IaaS servicesare accessedthroughthe Internet,sometimesthe performance mightbe notas
expected due to network latency.
4. When there is a need for more control on physical infrastructure:
Some organizations might require physical control over the underlying infrastructure. As the IaaS
servicesare abstractedasvirtual resources,itisnotpossibletohave morecontrol onunderlyingphysical
infrastructure.
Pros and Cons of IaaS:
The following are the benefits (Pros) provided by IaaS:
1. Pay-as-you-use model:
The IaaSservicesare providedtothe customersonapay-per-usebasis.Thisensuresthatthe customers
are requiredtopayforwhattheyhave used.Thismodeleliminatesthe unnecessaryspendingonbuying
hardware.
2. Reduced TCO (Total cost of ownership):
Since IaaS providers allow the IT users to rent the computing resources, they need not buy physical
hardware for running their business. The IT users can rent the IT infrastructure rather than buy it by
spendinglarge amount.IaaSreducestheneedfor buyinghardwareresourcesandthusreducesthe TCO.
3. Elastic resources:
IaaS providesresourcesbasedonthe currentneeds.IT userscan scale up or scale downthe resources
whenever they want. This dynamic scaling is done automatically using some load balancers. This load

balancer transfers the additional resource request to the new server and improves application
efficiency.
4. Better resource utilization:
Resource utilization is the most important criteria to succeed in the IT business. IaaS ensures better
resource utilization and provides high ROI for IaaS providers.
5. Supports Green IT:
In traditional IT infrastructure, dedicated servers are used for different businessneeds. Since many
serversare used,the powerconsumptionwillbe high.This doesnotresultinGreenIT.InIaaS,the need
of buyingdedicatedserversiseliminatedassingleinfrastructure issharedbetweenmultiplecustomers,
thusreducingthe numberof serverstobe purchasedandhence the powerconsumptionthatresultsin
Green IT.
The following are the drawbacks (Cons) of IaaS:
1. Security issues:
Since IaaS usesvirtualizationasthe enablingtechnology,hypervisorsplayanimportantrole.Thereare
many attacks that target the hypervisors to compromise it. If hypervisors get compromised, then any
VMs canbe attackedeasily.Mostof the IaaSprovidersare notable toprovide 100% securitytothe VMs
and the data stored on the VMs.
2. Interoperability issues:
There are no common standards followed among the different IaaS providers. It is very difficult to
migrate any VM from one IaaS providerto the other.Sometimes,the customersmightface the vendor
lock-in problem.
3. Performance issues:
IaaS isnothingbutthe consolidationof available resourcesfromthe distributedcloudservers.Here,all
the distributedserversare connectedoverthe network.Latencyof the networkplaysanimportantrole
in deciding the performance. Because of latency issues, sometimes the VM contains issues with its
performance.
Summary of IaaS Providers:
There are manypublicand private IaaSprovidersinthe marketwhoprovidesinfrastructure servicesto
the end users.
Table 5.1 provides the summary of popular infrastructure providers.
In the table, the popular IaaS providers are classifiedbased on the license, deployment model, and
supported host OS, guest OS, and hypervisors.

Platform as a Service:
In traditional application development,the application will be developedlocallyand will be hosted in
the central location.Most of the applicationsdevelopedbytraditional developmentplatformsresultin
a licensing-basedsoftware,whereasPaaSchanges the applicationdevelopmentfromlocal machine to
online. PaaS providers provide the development PaaS from the data center.
PaaS allows the developers to develop their application online and also allows them to deploy
immediatelyon the same platform. PaaS consumers or developerscan consume language runtimes,
applicationframeworks,databases, message queues,testingtools,anddeploymenttoolsasa service
over the Internet.
The developers can consume the services over the Internet as shown in Figure 5.6.

Services provided by PaaS providers:
Typical PaaS providers may provide programming languages, application frameworks, databases,and
testing tools as shown in Figure 5.7.
1. Programming languages:
PaaS providers provide a wide variety of programming languages for the developers to develop
applications. Some of the popular programming languages provided by PaaS vendors are Java, Perl,
PHP, Python, Ruby, Scala, Clojure, and Go.
2. Application frameworks:
PaaS vendors provide application frameworksthat simplifythe applicationdevelopment.Some of the
popular application development frameworks provided by a PaaS provider include Node.js, Rails,
Drupal, Joomla, WordPress, Django, EE6, Spring, Play, Sinatra, Rack, and Zend.
3. Database:
Since every application needs to communicate with the databases, it becomes a must-have tool for
every application. PaaS providers are providing databases also with their PaaS platforms. The popular
databases provided by the popular PaaS vendors are ClearDB, PostgreSQL, Cloudant, Membase,
MongoDB, and Redis.
4. Other tools:
PaaS providers provide all the tools that are required to develop, test, and deploy an application.
Characteristics of PaaS:
The following are the essential characteristics that make PaaS unique from traditional development
platforms:
1. All in one:
Most of the PaaS providersofferservicesto develop,test,deploy,host, and maintain applications in
the same IDE. Additionally,manyservice providersprovideallthe programminglanguages,frameworks,

databases, and other development-related servicesthat make developers choose from a wide variety
of development platforms.
2. Web access to the development platform:
PaaS provideswebaccesstothe developmentplatform.UsingwebUI,anydevelopercangetaccessto
the development platform. The web-basedUI helps the developerscreate, modify, test, and deploy
different applications on the same platform.
3. Offline access:
To enable offline development, some of the PaaS providers allow the developer to synchronize their
local IDEwiththe PaaSservices. The developerscandevelopanapplicationlocallyanddeployitonline
whenever they are connected to the Internet.
4. Built-in scalability:
Scalabilityisanimportantrequirementforthe new generationweborSaaSapplications. PaaSservices
provide built-in scalability to an application that is developed using any particular PaaS. This ensures
that the application is capable of handling varying loads efficiently.
5. Collaborative platform:
Most of the PaaS services provide support for collaborative development. To enable collaboration
amongdevelopers,mostof the PaaSprovidersprovide toolsforprojectplanning and communication.
6. Diverse client tools:
To make the development easier, PaaS providers provide a wide variety of client tools to help the
developer.The clienttoolsinclude CLI,webCLI,webUI, REST API,and IDE. The developerscanchoose
any tools of their choice. These client tools are also capable of handling billing and subscription
management.
Suitability of PaaS :
PaaS is a suitable option for the following situations:
1. Collaborative development:
To increase the time to marketand developmentefficiency,thereisaneedfora commonplace where
the developmentteamandotherstakeholdersof the applicationcancollaborate witheachother.Since
PaaS servicesprovide acollaborative developmentenvironment,itisa suitable optionforapplications
thatneedcollaborationamongdevelopersandotherthirdpartiestocarryoutthe developmentprocess.
2. Automated testing and deployment:
Automatedtestingandbuildingof anapplicationare veryusefulwhile developingapplicationsatavery
short time frame. The automated testing tools reduce the time spent in manual testing tools.Most of
the PaaS services offer automated testing and deployment capabilities. The developmentteam needs
to concentrate more on development rather than testing and deployment. PaaS services are the best
option where there is a need for automated testing and deployment of the applications.
3. Time to market:
The PaaSservicesfollowthe iterative andincrementaldevelopmentmethodologiesthatensurethatthe
application is in the market as per the time frame given.

Not Suitable Situations of PaaS:
There are some situations where PaaS may not be the best option:
1. Frequent application migration:
The major problem with PaaS services are vendor lock-in. Since there are no common standards
followedamong PaaS providers, it is verydifficultto migrate the application from one PaaS provider
to the other.
2. Customization at the infrastructure level:
PaaS is an abstracted service, and the PaaS users do not have full control over the underlying
infrastructure. There are some application development platforms that need some configuration or
customization of underlying infrastructure. In these situations, it is not possible to customize the
underlyinginfrastructure withPaaS.Ifthe application developmentplatformneedsany configuration
at the hardware level, it is not recommended to go for PaaS.
3. Flexibility at the platform level:
PaaS providestemplate-basedapplicationswhere all the differentprogramminglanguages,databases,
and message queues are predefined. It is an advantage if the application is a generic application.
4. Integration with on-premise application:
A company might have used PaaS services for some set of applications. For some set of applications,
they might have used on-premise platforms. Since many PaaS services use their own proprietary
technologies to define the application stack, it may not match with the on-premise application stack.
This makes the integration of application hosted in on-premise platform and PaaS platform a difficult
job.
Pros and Cons of PaaS
The PaaS has the following benefits (Pros):
1. Quick development and deployment:
PaaS providesall the requireddevelopmentandtestingtoolstodevelop,test,anddeploythe software
in one place. Most of the PaaS services automate the testing and deployment process as soon as the
developercompletesthe development.Thisspeedsupapplicationdevelopmentanddeploymentthan
traditional development platforms.
2. Reduces TCO:
The developersneednotbuylicenseddevelopmentandtestingtoolsif PaaSservicesare selected.Most
of the traditional development platforms requires high-end infrastructure for its working, which
increasesthe TCOof the applicationdevelopmentcompany.But,PaaSallowsthe developerstorentthe
software,developmentplatforms,andtestingtoolstodevelop,build,anddeploythe application.PaaS
doesnot require high-endinfrastructure alsoto developthe application,thusreducingthe TCO of the
development company.
3. Supports agile (Active) software development:
Nowadays, most of the new-generation applications are developed using agile methodologies.
Many ISVs and SaaS development companies started adopting agile methodologies for application

development. PaaS services support agile methodologies that the ISVs and other development
companies are looking for.
4. Different teams can work together:
The traditional developmentplatformdoesnothave extensive supportforcollaborative development.
PaaS services support developers from different places to work together on the same project. This is
possible because of the online common development platform provided by PaaS providers.
5. Ease of Use:
PaaS providesawide varietyof clienttoolssuchasCLI, webCLI,webUI, APIs,andIDEs. The developers
are free to choose any clienttoolsof theirchoice.Especially,the webUI–basedPaaS servicesincrease
the usability of the development platform for all types of developers.
6. Less maintenance overhead:
In on-premise applications, the development company or software vendor is responsible for
maintaining the underlying hardware. They need to recruit skilled administrators to maintain the
servers.Thisoverheadiseliminatedbythe PaaSservicesasthe underlyinginfrastructure ismaintained
by the infrastructure providers.
7. Produces scalable applications:
PaaS services are providing built-in scalability to the application that is developed using the PaaS
platform.
The PaaS has the following drawbacks (Cons):
1. Vendor lock-in:
The majordrawback withPaaS providersare vendorlock-in.The mainreasonfor vendorlock-inislack
of standards. There are nocommonstandards followedamongthe differentPaaSproviders. The other
reasonfor vendorlock-inisproprietarytechnologiesusedbyPaaSproviders.Mostof the PaaS vendors
use the proprietary technologies that are not compatible with the other PaaS providers. The vendor
lock-inproblemof PaaSservicesdoesnotallow the applicationstobe migratedfromone PaaSprovider
to the other.
2. Security issues:
Like inthe othercloudservices,securityisone of themajorissuesinPaaSservices.Since dataare stored
in off-premise third-partyservers,manydevelopersare afraidto go for PaaS services.Of course,many
PaaS providersprovide mechanismstoprotectthe userdata,andit isnot sufficienttofeel the safetyof
onpremise deployment.Whenselectingthe PaaSprovider,the developershouldreview the regulatory,
compliance, and security policies of the PaaS provider with their own security requirements. If not
properly reviewed, the developers or users are at the risk of data security breach.
3. Less flexibility:
PaaSprovidersdonotgive muchfreedomforthe developerstodefine theirownapplicationstack.Most
of the PaaS providersprovide manyprogramminglanguages,databases,andotherdevelopmenttools.
But, it isnot extensive anddoesnotsatisfyall developerneeds.Onlysome of the PaaSprovidersallow
developerstoextendthe PaaStoolswith the custom or new programminglanguages.Still mostof the
PaaS providers do not provide flexibility to the developers.
4. Depends on Internet connection:

Since the PaaS services are delivered over the Internet, the developers should depend on Internet
connectivity for developingthe application. Even though some of the providers allow offline access,
mostof the PaaSprovidersdonotallowoffline access.WithslowInternetconnection,the usabilityand
efficiency of the PaaS platform do not satisfy the developer requirements.
Summary of PaaS Providers:
PaaS providers are more in the IT market for public as well as the private clouds.
Table 5.2 gives a summary of popular private and public PaaS providers.

Software as a Service :
SaaS changesthe waythe software isdeliveredtothe customers.Inthe traditional software model,the
software isdeliveredasalicense-basedproductthatneedstobe installedinthe enduserdevice.Since
SaaS is deliveredasanon-demandservice overthe Internet,there isnoneedtoinstall the software to
the end user’s devices.
SaaS servicescanbe accessedordisconnectedatanytime basedonthe enduser’sneeds. SaaSservices
can be accessed from any lightweight web browsers on any devices such as laptops, tablets, and
smartphones.Some of the SaaSservicescanbe accessedfroma thinclientthatdoesnotcontainmuch
storage space and cannot run much software like the traditional desktop PCs.
The important benefits of using thin clients for accessing the SaaS application are as follows: it is less
vulnerable to attack, has a longer life cycle, consumes less power, and is less expensive.
Services provided by SaaS Providers:
A typical SaaS provider may provide business services, social networks, document management, and
mail services as shown in Figure 5.8:
1. Business services:
Most of the SaaS providers started providing a variety of business services that attract start-up
companies. The business SaaS services include ERP, CRM, billing, sales, and human resources.
2. Social networks:
Since social networkingsitesare extensivelyusedbythe general public,manysocialnetworkingservice
providersadoptedSaaSfortheirsustainability.Since the numberof usersof the social networkingsites
is increasing exponentially, cloud computing is the perfect match for handling the variable load.
3. Document management:
Since mostof the enterprisesextensivelyuse electronicdocuments,mostof the SaaSprovidersstarted
providing services that are used to create, manage, and track electronic documents.

4. Mail services:
E-mail servicesare currentlyusedbymany people.The future growthine-mail usage isunpredictable.
To handle the unpredictable number of users and the load on e-mail services, most of the e-mail
providers started offering their services as SaaS services.
Characteristics of SaaS:
1. One to many:
SaaS servicesare deliveredasa one-to-manymodel where asingle instance of the application can be
shared by multiple tenants or customers.
2. Web access:
SaaS servicesprovide webaccesstothe software. Itallowsthe enduserto access the applicationfrom
any location if the device is connected to the Internet.
3. Centralized management:
Since SaaS services are hosted and managed from the central location, management of the SaaS
application becomes easier.Normally, the SaaS providers will perform the automatic updates that
ensure that each tenant is accessingthe most recentversionof the application withoutany user-side
updates.
4. Multidevice support:
SaaS services can be accessed from any end user devices such as desktops, laptops, tablets,
smartphones, and thin clients.
5. Better scalability:
Since mostof the SaaS servicesleveragePaaSandIaaS for itsdevelopmentanddeployment,itensures
a better scalability than the traditional software. The dynamic scaling of underlyingcloud resources
makes SaaS applications work efficiently even with varying loads.
6. High availability:
SaaS services ensure the 99.99% availability of user data as proper backup and recovery mechanisms
are implemented at the back end.
7. API integration:
SaaS serviceshave the capabilityof integrating with other software or service through standard APIs.
Suitability of SaaS:
SaaS applications are the best option for the following:
1. On-demand software:
The licensing-basedsoftwaremodelrequiresbuyingfullpackagedsoftwareandincreasesthe spending
on buying software. Some of the occasionally used software does not give any ROI. Because of this,
manyendusersare lookingfora software thattheycan use as and whentheyneeded.If the endusers
are looking for on-demand software rather than the licensing-based full-term software,then the SaaS
model is the best option.
2. Software for start-up companies:

When using any traditional software, the end user should buy devices with minimum requirements
specified by the software vendor. This increases the investment on buying hardware for start-up
companies. Since SaaS services do not require high-end infrastructure for accessing, it is a suitable
optionfor start-up companies that can reduce the initial expenditure on buying high-end hardware.
3. Software compatible with multiple devices:
Some of the applicationslike wordprocessorsormail servicesneedbetteraccessibilityfromdifferent
devices. The SaaS applications are adaptable with almost all the devices.
4. Software with varying loads:
We cannot predict the load on popular applications such as social networking sites. The user may
connect or disconnect from applications anytime. It is very difficult to handle varying loads with the
traditional infrastructure. With the dynamic scaling capabilities, SaaS applications can handle varying
loads efficiently without disrupting the normal behavior of the application.
Not Suitable Situations of SaaS:
The SaaS delivery model is not the best option for the applications mentioned in the following:
1. Real-time applications:
Since SaaS applications depend on Internet connectivity, it may not work better with low Internet
speed. If data are stored far away from the end user, the latency issues may delay the data retrieval
timings. Real-time applications require fast processing of data that may not be possible with the SaaS
applications because of the dependency on high-speed Internet connectivity and latency issues.
2. Applications with confidential data:
Data security, data governance, and data compliance are always issues with SaaS applications. Since
data are stored with third-party service providers, there is no surety that our data will be safe. If the
storedconfidential datagetlost,it will make a seriouslossto the organization.Itis not recommended
to go for SaaS for applications that handle confidential data.
3. Better on-premise application:
Some of the on-premise applications might fulfill all the requirements of the organization. In such
situations, migrating to the SaaS model may not be the best option.
Pros and Cons of SaaS :
SaaS services provide the following benefits:
1. No client-side installation:
SaaS services do not require client-side installation of the software. The end users can access the
servicesdirectlyfromtheservice providerdatacenterwithoutanyinstallation.Thereisnoneedof high-
end hardware to consume SaaSservices. It can be accessed from thin clients or any handheld devices,
thus reducing the initial expenditure on buying high-end hardware.
2. Cost savings:
Since SaaS servicesfollow the utility-basedbillingorpay-as-you-gobilling,itdemandsthe endusersto
pay for what they have used. Most of the SaaS providers offer different subscription plans to benefit
differentcustomers.Sometimes,the genericSaaSservicessuchaswordprocessorsare givenforfreeto
the end users.

3. Less maintenance:
SaaS services eliminate the additional overhead of maintaining the software from the client side.For
example, in the traditional software, the end user is responsible for performing bulk updates. But in
SaaS, the service provider itself maintains the automatic updates,monitoring,and other maintenance
activities of the applications.
4. Ease of access:
SaaS services can be accessed from any devicesif it is connected to the Internet. Accessibilityof SaaS
services is not restricted to any particular devices. It is adaptable to all the devices as it uses the
responsive web UI.
5. Dynamic scaling:
SaaS servicesare popularlyknownforelasticdynamicscaling.Itisverydifficultforon-premisesoftware
toprovide dynamicscalingcapabilityasitrequiresadditionalhardware.Sincethe SaaSservicesleverage
elastic resources provided by cloud computing, it can handle any type of varying loads without
disrupting the normal behavior of the application.
6. Disaster recovery:
With proper backup and recovery mechanisms, replicas are maintainedfor every SaaS services. The
replicas are distributed across many servers. If any server fails, the end user can access the SaaS from
otherservers.It eliminatesthe problemof single pointof failure.Italsoensuresthe highavailabilityof
the application.
7. Multitenancy:
Multitenancy is the ability given to the end users to share a single instance of the application.
Multitenancy increases resource utilization from the service provider side.
The following are the major problems(Drawbacks or Cons) with SaaS services:
1. Security:
Security is the major concern in migrating to SaaS application. Since the SaaS application is shared
betweenmanyendusers,there isa possibilityof dataleakage.Here,the dataare storedin the service
providerdata center.We cannot simplytrustsome third-partyservice providertostore our company-
sensitiveand confidential data.Theendusershouldbe carefulwhileselectingtheSaaSprovidertoavoid
unnecessary data loss.
2. Connectivity requirements:
SaaS applications require Internet connectivity for accessing it. Sometimes, the end user’s Internet
connectivitymightbe veryslow.In such situations,the usercannot access the serviceswithease.The
dependency on high-speed Internet connection is a major problem in SaaS applications.
3. Loss of control:
Since the dataare storedinathird-partyandoffpremise location,theenduserdoesnothaveanycontrol
over the data. The degree of control over the SaaS application and data is lesser than the on-premise
application.

Summary of SaaS Providers
There are many SaaS providers who provide SaaS services such as ERP, CRM, billing, document
management, and mail services.
Table gives a summary of popular SaaS vendors in the market.
Other Cloud Service Models:
Many service providersalreadystartedofferingseparateservicessuch asnetwork,desktop, database,
and storage on demand as given in the following:
1. Network as a Service (NaaS):
Naas is an ability given to the end users to access virtual network services that are provided by the
service provider. Like other cloud service models, NaaS is also a business model for delivering virtual
networkservicesoverthe Internetona pay-per-use basis.Inon-premise datacenter,the IT industries
spent a lot of money to buy network hardware to manage in-house networks. But, cloud computing
changesnetworkingservicesintoautility-basedservice.NaaSallowsnetworkarchitectstocreatevirtual
networks,virtual networkinterface cards(NICs),virtual routers,virtual switches,andothernetworking
components. Additionally, it allows the network architect to deploy custom routing protocols and
enables the design of efficient in-network services, such as data aggregation, stream processing,and
caching. Some of the popular services provided by NaaS include virtual private network (VPN),
bandwidth on demand (BoD), and mobile network virtualization.
2. Desktop as a Service (DEaaS) :
Desktop as a Service (DEaaS) isan abilitygivento the endusers to use desktop virtualizationwithout
buying and managing theirown infrastructure. DEaaS is a pay-per-use cloudservice deliverymodelin
whichthe service providermanagesthe back-endresponsibilitiesof datastorage,backup,security,and
upgrades. The end users are responsible for managing their own desktop images, applications, and
security.Accessingthe virtual desktopprovidedbythe DEaaS providerisdevice,location,andnetwork
independent.DEaaSservicesare simpletodeploy,are highlysecure,andproduce betterexperienceon
almost all devices.
3. Storage as a Service (STaaS):

STaaS is an ability given to the end users to store the data on the storage services provided by the
service provider. STaaS allows the end users to access the files at any time from any place.The STaaS
provider provides the virtual storage that is abstracted from the physical storage of any cloud data
center.STaaS is also a cloud businessmodel thatisdeliveredasa utility.Here,the customerscan rent
the storage from the STaaS provider.STaaSis commonlyusedasa backup storage for efficientdisaster
recovery.
4. DataBase as a Service(DBaaS):
DBaaS is an ability given to the end users to access the database service without the need to install
and maintain it. The service provider is responsible for installing and maintaining the databases. The
end users can directly access the servicesand can pay according to their usage. DBaaS automates the
database administration process. The end users can access the database services through any API or
web UIs provided by the service provider. The DBaaS eases the database administration process.
Popular examples of DBaaS include SimpleDB, DynamoDB,MongoDB as a Service, GAE datastore, and
ScaleDB.
5. Data as a Service (DaaS) :
DaaS is an ability givento the end users to access the data that are providedby the service provider
over the Internet. DaaS provides data on demand. The data may include text, images, sounds, and
videos.DaaSiscloselyrelatedtoothercloudservice modelssuchasSaaSand STaaS.DaaS can be easily
integratedwithSaaSorSTaaSforprovidingthe compositeservice.DaaSishighlyusedingeographydata
servicesandfinancial dataservices.The advantagesof DaaSinclude agility,costeffectiveness, anddata
quality.
6. Security as a Service(SECaaS):
SECaaS is an ability given to the end user to access the security service provided by the service
provider on a pay-per-use basis. In SECaaS, the service provider integrates their security services to
benefit the endusers.Generally, the SECaaS includesauthentication, antivirus, antimalware/spyware,
intrusion detection, and security event management. The security services provided by the SECaaS
providers are typically used for securing the on-premise or in-house infrastructure and applications.
Some of the SECaaS providers include Cisco, McAfee, Panda Software, Symantec, Trend Micro, and
VeriSign.
7. Authentication as a Service( IDaaS):
IDaaS is an abilitygivento the end usersto accessthe authenticationinfrastructure that is managed
and providedby the third-party service provider. The end userof IDaaS is typicallyanorganizationor
enterprise.UsingIDaaSservices,anyorganizationcaneasilymanage theiremployees’identitywithout
any additional overhead. Generally,IDaaS includes directory services,federated services,registration,
authentication services, risk and event monitoring, single sign-on services, and identity and profile
management.
8. Everything as a Service (XaaS):
Now, cloudcomputing movesto the scenario where everythingcan be givenas a service.Thiscan be
termedas Everythingas a Service (XaaS). Inthe future,we expectmanynew servicemodelstoachieve
the goal Cloud Service Models of XaaS.
XaaS may include
(1) Backup as a Service (BaaS)
(2) Communication as a Service (CaaS)

(3) Hadoop as a Service (HaaS)
(4) Disaster Recovery as a Service (DRaaS)
(5) Testing as a Service (TaaS)
(6) Firewall as a Service (FWaaS)
(7) Virtual Private Network as a Service (VPNaaS)
(8) Load Balancers as a Service (LBaaS)
(9) Message Queue as a Service (MQaaS)
(10) Monitoring as a Service (MaaS)

Unit iv

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Unit iv