J Internet Serv Appl(2011)2:81–94
DOI10.1007/s13174-011-0027-x
S I:F U T U R E N E T S E RV I C E M O D E L S&D E S I G N S
Cloud computing rvices:taxonomy and comparison C.N.Höfer·G.Karagiannis
Received:1February2011/Accepted:18May2011/Published online:19June2011
©The Author(s)2011.This article is published with open access
Abstract Cloud computing is a highly discusd topic in the technical and economic world,and many of the big play-ers of the software industry have entered the development of cloud rvices.Several companies what to explore the possibilities and benefits of incorporating such cloud com-puting rvices in their business,as well as the possibili-ties to offer own cloud rvices.However,with the amount of cloud computing rvices increasing quickly,the need for a taxonomy framework ris.This paper examines the available cloud computing rvices and identifies and ex-plains their main characteristics.Next,this paper organizes the characteristics and propos a tree-structured taxon-omy.This taxonomy allows quick classifications of the dif-ferent cloud computing rvices and makes it
easier to com-pare them.Bad on existing taxonomies,this taxonomy provides more detailed characteristics and hierarchies.Ad-ditionally,the taxonomy offers a common terminology and baline information for easy communication.Finally,the taxonomy is explained and verified using existing cloud r-vices as examples.
Keywords Cloud computing·Taxonomy·Classification·Comparison
1Introduction
pattyCloud computing(CC)is currently one of the biggest buz-zwords and the amount of cloud computing rvices(CCSs) C.N.Höfer( )·G.Karagiannis
University of Twente,Enschede,The Netherlands
hofer@student.utwente.nl
G.Karagiannis
e-mail:g.karagiannis@utwente.nl is increasing rapidly.Many big players of the software in-dustry,such as Microsoft,as well as other Internet tech-nology heavyweights,including Google and A
mazon,are joining the development of cloud rvices[5,31,39,43, 51,67].Several business,also tho not technically ori-ented,want to explore the possibilities and benefits of cloud computing[36].However,there is a lack of standardization of cloud computing rvices[28,39,51],and each cloud rvice provider us different technologies,protocols,and formats.Further,most clouds are very vague about the ac-tual internal workings.All this makes interoperability when working with multiple rvices or migrating to new r-vices difficult.Additionally,there is a big marketing hype around cloud computing,where providers of online rvices re-brand their products to be part of the cloud movement [50].The great amount of different cloud computing r-vices makes it hard to compare the offers and tofind the right rvice.
The vast amount of cloud computing rvices and the lack of universal definitions and standards lead to the ques-tion whether cloud computing rvices can be classified in a taxonomy bad on their characteristics to easily compare them.
Table-bad comparisons of cloud computing rvices exist[59],however,they are mainly for commercial u and the degree of detail varies greatly.In[55],a taxonomy has been propod.However,[55]aims tofind the strengths, weakness,and challenges in current cloud systems,rather than providing a method to categorize and compare existing and future cloud comput
ing rvices.Moreover,[71]pro-vides a state of the art and rearch challenges in the area of cloud computing.However,also[71],does not provide a method to categorize existing and future cloud computing rvices.Further,also the industry has published white pa-pers describing cloud computing taxonomies,such as[37]
by Intel Cooperation.Intel’s white paper shows five cate-gories and explains possible applications and rvices that can be offered for each.More distinctive characteristics of the rvices are not considered.
In this paper,a new,tree-structure bad taxonomy is de-veloped,which helps to easily and quickly co
mpare exist-ing and future cloud computing rvices.The classification can also help rearchers identify areas that could be stan-dardized.Additionally,the taxonomy offers a common ter-minology for easy understanding and communication about cloud computing rvices and their characteristics.The tax-onomy will be bad on current major cloud computing r-vices,such as the Google App Engine [26], [57]and Amazon EC2[2];but also new developments,such as the Eucalyptus platform [20],will be considered.The main focus is on cloud computing rvices for corporate u.
First,the current cloud computing rvices are examined and their characteristics are identified and explained.For this analysis,recent surveys and studies in the field of cloud computing rvices,as well as the information provided by the cloud rvice providers is considered.Next,the charac-teristics are organized to form the taxonomy.Then the tax-onomy is explained and possible options for extension are given.Finally,the taxonomy is verified using existing cloud rvices.
This paper is an extended version of [32],which has been published at the EFSOI Workshop at Globecom,in Decem-ber 2010.Here,we extended the rearch by updating the work with more recent information and by considering addi-tional issues of cloud computing rvices.The introduction to cloud computing has been extended to give a more com-plete overview and definition.
Further,during the study of clouds a difference in the amount of available information on the cloud rvices has been noticed.This has been added to the taxonomy as an additional “Openness”characteristic.Additionally,more characteristics to extend the taxonomy are described in a parate ction and the u and extension possibilities of the taxonomy have been explained in more detail.Moreover,additional examples are included on clas-sifying cloud computing rvices in the taxonomy.A perfor-mance analysis of the taxonomy itlf is outside the scope of this paper.This has to be evaluated after the taxonomy has been ud in further rearch.
The remainder of this paper is organized as follows.Next,Sect.2gives the definition of cloud computing that is to be ud in our work.Section 3prents the current cloud computing rvices.Section 4describes their main charac-teristics.The design of the taxonomy is discusd in Sect.5.The classification of cloud computing rvices in the tax-onomy,as well as the u of the taxonomy for comparison is discusd in Sect.6using current cloud computing r-vices.Finally,Sect.7concludes and it recommends future
work.
Fig.1Cloud computing rvices美国总统辩论第3场
2Cloud computing overview
A cloud can be en as a scalable infrastructure that sup-ports and interconnects veral cloud computing rvices;e Fig.1.The cloud itlf consists “of a collection of inter-connected and virtualized computers that are dynamically provisioned and prented as one or more unified comput-ing resource(s)”[10].The clients that are the urs of the cloud computing rvices,u their home or work com-puter or any other Internet-enabled device to connect and u the cloud computing rvices.Generally,rvice-level agreements guard the provisioning of the cloud rvices.The key attributes that distinguish cloud computing from traditional computing solutions have been identified in [5,37,46,65,71]and generally compri the following:•Underlying infrastructure and software is abstracted and offered as a rvice.
•Build on a scalable and flexible infrastructure.
•Offers on-demand rvice provisioning and quality of r-vice (QoS)guarantees.
•Pay for u of computing resources without up-front com-mitment by cloud urs.•Shared and multitenant.
•Accessible over the Internet by any device.
The state of the art and rearch challenges of cloud com-puting rvices have been described in [51,65,71].More-over,[51,65,71]describe the cloud computing architecture and the enabling technologies in more detail.The main un-derlying technologies are virtualization technologies to pro-vide flexible and scalable computing platforms,Web r-vices and Service Oriented Architectures (SOA)to man-age cloud rvices,and distributed storage for backup and world-wide data access [65].
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The National Institute of Standards and Technology (NIST)propod the following definition of cloud comput-ing:“Cloud computing is a model for enabling convenient,
Fig.2The three main categories of cloud computing rvices[71
sayno
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on-demand network access to a shared pool of configurable computing ,networks,rvers,storage,ap-plications,and rvices)that can be rapidly provisioned and relead with minimal management effort or rvice provider interaction.This cloud model promotes availabil-ity.”[40].This definition will be ud as the basis for distin-guishing cloud computing rvices and traditional Internet rvices.
Next,three rvice models are currently being differen-tiated—Software-as-a-Service(SaaS),i.e.,online appli-cations,such as web-bad email,Platform-as-a-Service (PaaS),which allows customers to deploy their own appli-cations,and Infrastructure-as-a-Service(IaaS),which pro-vides,for example,processing power or storage[40].Some previous work considers additional rvice models,such as Service-as-a-Service[37],and Data-as-a-Service[31,65] or Storage-as-a-Service[31],but generally it is possible to group the with the existing three rvice models.How-ever,beyond the rvice models no further categories are considered in current definitions.
Several cloud architectures have been propod.A refer-ence architecture and implementation of a s
李阳疯狂英语听力下载ervice-oriented infrastructure(SOI)using open standards and recent virtual-ization and SOI technologies is the European Union funded RESERVOIR project[52,56].The RESERVOIR architec-ture has been developed jointly with IBM and is described in[56].Another architecture is Aneka,which is a bad PaaS architecture for building applications[63].
ontarioA market-oriented implementation of the Aneka architec-ture has been described in[10].In[33],IBM describes a rvice-oriented framework for building a low-cost,scal-able,and cured platform for web-delivered business r-vices[33].Finally,in[60],a description of each of the ar-chitectures is given and an additional rvice-oriented cloud computing architecture is propod.3Current cloud computing rvices
The main differences between the cloud computing rvices that are deployed are related to the type of rvice offered, such as(1)storage space and computing power,(2)plat-forms for own software deployment,or(3)online software applications,ranging from web-email to business analysis tools.Bad on the differences,the NIST has already pro-pod three main categories of cloud computing rvices [40].The three rvice models are depicted in Fig.2.In this ction,a few cloud computing rvices of each cate-gory will be discusd to gain an overview of the existing rvices.Existing taxonomies[31,55]and related work[59, 66]have been considered to make a lecti
on of the current cloud computing rvices for this overview.As additional source of information the websites of the cloud rvices have been ud to provide more details on the rvice.
3.1Infrastructure as a rvice
Cloud infrastructure rvices typically offer virtualization platforms,which are an evolution of the virtual private rver offerings,that are already known for years[31].The customers buy the resources,instead of having to t up rvers,software,and data center space themlves,and get billed bad on the resources consumed.They deploy their own software on the virtual machines and control and man-age it.The virtual instances can be rented for as long as nec-essary,which can be as short as an hour.The amount of in-stances can be scaled dynamically to fulfill the customers’needs.Billing is bad on this amount,the duration,and additional rvices ud,such as additional storage space. Providers often have data centers in multiple locations to offer quick access all over the world.Web interfaces allow monitoring of the cloud rvice.
Some providers make it possible to connect the virtual instances to the company’s network via VPN(Virtual Pri-vate Network),to make the company network em like one big scalable IT infrastructure.The solutions are called hy-brid clouds,as they connect the company’s(internal)private cloud with the public cloud of the IaaS provider[51].
A pioneer in virtualization and computing power offer-ings is Amazon[2].The Amazon Elastic Compute Cloud (EC2)is one of the most widely ud infrastructure plat-forms[31].Further popular virtualization rvices include ServePath’s GoGrid[25]and the Rackspace Cloud[53]. Other rvices are the IBM Smart Business cloud solu-tions[34],Oracle Cloud Computing[49],GigaSpaces[24], RightScale[54],and Nimbus[61].
Online storage and backup rvices fall in the category of IaaS.Like most virtualization platforms,there are veral storage solutions intended for corporate u,but there are also special rvices for private individuals.Corporate r-vices range from temporal to permanent and from general additional storage space to extend the company’s internal capabilities,to storage rvices aimed at databa-structured information.The latter rvices are billed bad not only on the amount of storage space ud,but also on the amount of queries on the data.Further,there are specially designed rvices to extend the storage amount offered with standard virtualization instances.
libyaFor private individuals more and more cloud storage and backup rvices are offered.Laptop and netbook manufac-turers,as well as,operating system providers adverti for additional web-storage.Files can be stored on the provider’s rvers as backup or to synchronize multiple workstatio
ns and can often be retrieved from different locations,as the rvices are often accessible also with a web-browr,such as Rackspace’s CloudFiles[53].
Rackspace offers online storage for corporate and private u[53].Another storage provider is Nirvanix[44].Amazon offers data storage facilities either in combination or pa-rate from their EC2instances,called Amazon Elastic Block Store(EBS)and Amazon Simple Storage Service(S3),re-spectively[2].Amazon also provides special databa solu-tions,such as the Amazon SimpleDB[2].
3.2Platform as a rvice
PaaS providers offer a managed higher-level software in-frastructure,where customers can build and deploy partic-ular class of applications and rvices using the tools,en-vironments,and programming languages supported by the provider.The offers include the u of the underlying in-frastructure,such as rvers,network,storage,or operating systems,over which the customers have no control,as it is abstracted away below the platform[31,40].
Platform rvices are mostly aimed at specific domains, such as the development of web applications,and are depen-dent on the programming language.Customers get a pa-rated environment to test and develop or to permanently de-ploy their applications.Google’s App Engine is
targeted at traditional web applications offering a Java or Python envi-ronment[26].For small nonscaling applications,the Google App Engine is free.On Microsoft’s Azure platform,appli-cations can be developed using the libraries[5].Mi-crosoft us their cloud offers to promote their own software packages[31].
Bungee Connect is specifically designed for cloud appli-cation development and deployment[9].A PaaS of a dif-ferent domain [23],which allows companies to develop customized business applications,similar to the offerings
3.3Software as a rvice
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Cloud software offerings typically provide specific,al-ready-created applications running on a cloud infrastructure.
A very well-known SaaS is the web-bad e-mail.Most soft-ware cloud computing rvices are web-bad applications, which can be accesd from various client devices through a thin client interface,such as a web browr.The customers of the rvices do not manage or control the underlying infrastructure and application platform;only limited ur-specific configurations are possible.Features in standard nonremote software applications providing Internet-bad storage are
also often considered to be part of SaaS offer-ings.
A software cloud rvice intended for corporate u is rvice[57],which offers business anal-ysis and customer relationship management(CRM)tools. Appian Anywhere is another domain specific SaaS offer-ing business process management tools[4].Popular soft-ware rvices also intended for private u are the Google Apps.The include calender,contacts web-bad email, and chat capabilities,as well as the Google Docs package [27,30],which allows access and sharing of documents, spreadsheets,and prentations.Another document sharing and backup rvice is Box[7].SmugMug is intended for video and photo sharing and us Amazon S3[58].
3.4Open-source bad rvices
Although some cloud rvice providers u open-source software or platforms,the ba systems are usually propri-etary.However,there are a few entirely open-source bad platforms,as well as applications and tools available to man-age mainly IaaS cloud rvices.The tools allow the ur to monitor,manage and control the virtual instances.
Unfortunately,most open-source cloud computing r-vices are at the infrastructure or platform level and very
few SaaS open-source applications exist.Further,almost all open-source platforms are bad on Linux operating-systems limiting the customer group to the operating-systems[68].
The Eucalyptus cloud is mainly aimed at private clouds [20].Groundwork is a commercial open-source cloud man-agement system that works with Amazon’s EC2[29].Open-Nebula is a“standard-bad open-source toolkit to build private,public,and hybrid clouds”[48]and can be ud with the Amazon EC2rvice.The Nimbus project is also built on an open-source basis.It is maintained by the Uni-versity of Chicago and was t up for scientific computa-tions[61].
3.5New developments
New developments include the offering of computer-games that are completely hosted in the cloud.This will make portability easier,as the game can be resumed from a dif-ferent location[19].Also,it is less dependent on the ur’s hardware and less prone to piracy.
A rather new and not yet commercially available idea is the offering of cloud computing resources,such as com-puting power and data storage,to support smart phones and other resource-starved devices[1,35].Since mobile phones have limited processing power,storage space,and battery life,such an offer would make it possible to run more sophisticated applications and offer more rvic
es to smart phone urs[42].The rvices could be provided through Wi–Fi and3G connections,and eventually,4G and WiMax[42].
4Main characteristics of cloud computing rvices
As en above many different cloud computing rvices ex-ist.The most apparent difference,the type of rvice offered, has been addresd.In this ction,the common characteris-tics of Iaas,Paas,and SaaS cloud rvices will be examined. Then for each category,more specific characteristics will be discusd.It is likely that the list can be expanded further, however,the lected characteristics allow more clear dis-tinctions at each level of the taxonomy.A few additional cat-egories that can be ud for future expansion are described in Sect.4.3.
4.1Common characteristics
The shared characteristics are the licen type,the intended ur group,the curity offered,formal agreements between the provider and the customer,as well as payment systems, interoperability,and adherence to standards.In the follow-ing ctions,each of the features will be discusd.4.1.1Licen type
curly是什么意思
Most cloud computing rvices u proprietary software and licens.However,veral cloud computing providers make u of open-source software and platforms.Amazon us the open-source Xen technologies[2]and Google’s PaaS offering is built around the open-source Python program-ming language[26],but their core cloud computing r-vice and additional rvices are kept clod-source.A lot of cloud monitoring software is open-source bad,as well as smaller cloud computing rvices,since small players often lack the power and influence to push proprietary software on the market[31].
Licen types also play a role when offering infrastruc-ture-and platform-level rvices.IaaS providers do not suf-fer from software licensing issues when renting out their vir-tual rvers without operating systems installed.However, when including operating systems and software packages, this can cau potential problems as to how the customer should be billed when using the rvice for a limited time-period.Often additional fees for the software u need to be paid.Other platforms only u their own software,such as Microsoft Azure.Software licensing has been identified as
a current obstacle for cloud computing in[5,31,45].
4.1.2Intended ur group
Some cloud computing rvices differentiate between cor-porate and private u.Most IaaS and PaaS offerings are intended for companies,whereas SaaS offerings exist for corporations,private individuals or both,such as the Google Apps[27].However,this does not imply,that rvices aimed at companies cannot be purchad by individuals.
A further distinction in the corporate and private ur group can be made between mobile andfixed urs.Mo-bile urs access their cloud computing rvices from any-where,be it at the office,at home,form a desktop,laptop,or hand-held.Fixed urs are stationary and typically u the same device to connect to the rvice.Once cloud comput-ing rvices intended to support smart phones and other low-resource devices are available(e Sect.3.5),an additional group,bad on this hardware type,can be considered.
4.1.3Security and privacy
Security and privacy are important aspects,especially when important data resides on the cloud’s rvers.Loss or leak of data cannot just cau loss of revenues but also legal ac-tions[43].In particular,when handling personal data,cer-tain regulations may apply,such as the European Union di-rectives2002/58/EC[22]and95/46/EC[21].The EU’s data protection laws state,for example,that data may only be stored in countries with adequate protection and for certain
data it is necessary to know the physical location of the data, which is not always possible when using cloud computing technologies.Due to the abnce of standards,cloud cu-rity,data privacy,and ownership are approached differently by each provider[70].
Generally,encryption and authentication should be ud on all cloud rvices.Encryption can guard,for example, against interception between virtual machines at network level[64].For the taxonomy,the curity measures are di-vided into external curity,which considers the curity measures,the cloud provides to cure the access to the cloud,and the internal curity,which address the internal curity mechanisms the cloud offers to parate and cure the different virtual instances and clients within the cloud. The latter is left for future expansion of the taxonomy and is discusd in Sect.4.3.2.
electionMost cloud rvices can be accesd with a web-browr and the standard HTTP(Hyper Text Transfer Protocol)is ud to connect to the cloud.To provide encryption and cure identification of the rver SSL/TLS(Secure Socket Layer/Transport Layer Security)is ud.Further curity approaches ud for authentication and authorization in-clude PKI(Public Key Infrastructure)and X.509SSL cer-tificates[70].However,the mechanisms need to be im-plemented properly.The Amazon EC2us public-keys for authentication[64].
For hybrid clouds,VPN s are ud[51].The Amazon Vir-tual Private Cloud(Amazon VPC)rvice does this[2]. 4.1.4Payment systems
The payment system ud for cloud computing rvices is one of the distinguishing characteristics.The main differ-ence between the traditional form is that true cloud rvices are billed bad on dynamic u[31,66].Rather than paying afixed monthly or yearly charge,the customer only pays for the resources consumed.The resources could be the number of virtual instances,data storage amount,bandwidth,com-pute time and resources(CPU or RAM),and transactions (measured in Gets and Puts for databas),as well as com-binations of the.
Still cloud computing rvices can u different pay-ment systems,bad on the resources ud.The most fre-quently ud pricing model is pay-per-u,in which(re-source)units or units per time are associated withfixed price values[66].When using dynamic or variable pricing,the price is established as a result of dynamic supply and de-mand,for example,as the means of auctions or negotia-tions[66]. us dynamic pricing[72].A few cloud rvices are free of charge,such as Google Docs and the Google App Engine(free up to a certain level of comput-ing resources)[26].Customers of Amazon EC2are billed monthly for the resources ud bad on the pay-per-u model[2,59].GoGrid urs can choo between pay-as-you-go ,customers only pay for the
resources they deploy,or prepaid plans,for which customers get“a prepaid allotment of cloud rver resources at a discounted rate for afixed monthly cost”[25].
4.1.5Standardization
Standardization refers to the u of common API s(Appli-cation Programming Interface)and architectures,as well as, technical standards.The standards can either be approved and“maintained by an organization such as ANSI or the ISO,or they can simply implement a commonly-ud or fa-miliar interface(de facto standards)”,from[31].
So far,there are no clearly defined and widely adopted standards,though this would be beneficial to cloud com-puting customers and rvice developers.Standards would increa interoperability and allow possible customization, due to the technical transparency.Further benefits include price advantages and greater availability of substitutes,be-cau of incread competition.
Standardization can be applied to cloud architectures, protocols,cloud rvice identifiers and description lan-guages,as well as formats,virtualization technologies,and rvice-level agreements.The ETSI(European Telecommu-nications Standards Institute)TC CLOUD has identified the current standardization requirements for cloud computing rvices in[45].
There are veral organizations attempting to create such standards[28],including the Cloud Computing Interoper-ability Forum,which tries to develop a framework that en-ables two or more clouds to exchange information[12]. Sponsors include IBM,Sun Microsystems,Intel,and Cisco. The DMTF’s Open Cloud Standards Incubator also aims to standardize interactions between clouds by creating“re-source management protocols,packaging formats and cu-rity mechanisms to facilitate interoperability”[18].Further, the DTMF also maintains the Open Virtualization Format (OVF).The Open Cloud Consortium provides testbeds for cloud computing[47].The Cloud Security Alliance(CSA) is working on standards for curity and privacy and aims to promote“best practices for providing curity assurance within Cloud Computing,and to provide education on the us of Cloud Computing to help cure all other forms of computing”[15].As mentioned earlier,the NIST has pro-pod and is further working on a definition for cloud com-puting[40].The Cloud Standards Wiki tries to gather infor-mation about the different organizations working on stan-dards and definitions[16].
4.1.6Formal agreements
The most commonly ud formal agreements are rvice level agreements(SLA),which formally define which level
