a conceptual platform of sla in cloud computing

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A Conceptual Platform of SLA in Cloud Computing

MinChao Wang, Xing Wu*, Wu ZhangSchool of computer engineering and science

Shanghai UniversityShanghai, China

[email protected]

FuQiang Ding, Jun Zhou, GuoCai PeiChina Telecom Shanghai Ideal Information

Industry(Group) Co. Ltd.Shanghai, China

Abstract Cloud computing is a promising technology, wherethe infrastructure, developing platform, software and storageare delivered as a service. With the development of cloudcomputing, more and more cloud service providers emerge.However, there are no metrics can be referred to comparethese providers, so it is difficult for cloud consumers to selectthe most reliable providers or resources. Thus we present aplatform of Services Level Agreement (SLA) in cloudcomputing. In the platform, we propose a Reputation Systemto evaluate the reliability of providers or resources to addressthis challenge, and we also propose a SLA template pool inorder to make the SLA negotiation between cloud providersand cloud consumers become more equitable, transparent andconvenient.

Keywords-SLA, Cloud computing, Reputation System, SLAnegotiation

I. INTRODUCTIONWith the rapid growth on the amount of data in the

internet age, calculation capacity of PC can not meet thedemand of large-scale, massive data scientific computing.Moreover, the gradual failure of Moore's Law[1] also

verifies the fact parallel computing is becoming main trendin scientific computing. Cloud computing is the newcalculation form in parallel computing and has emerged asan effective technology, where the computing infrastructure,networking routers, software, and developing platform aredelivered as a service available for users at any time andthrough which they can access the Internet[2]. After IBMand Google announced to cooperate in cloud computing,cloud computing has attracted the attention of scholars andquickly became a hot research topic in industry andacademe. Currently there are some famous cloud systemssuch as Amazon EC2 Google App Engine ApacheHadoop.

Cloud computing make computer services change to such

a Service-Oriented Architecture and hence the quality of services and the reliability of services provider becomeimportant aspects in this architecture. Moreover, with theincrease of public cloud providers, cloud consumers facevarious challenges such as the security, privacy, anddiscovery of reliable resource providers[3]. However, for thedifferent services, customers demands are always different.So it is not possible to fulfill all consumer expectations fromthe service provider perspective and hence a balance needs to

be made via a negotiation process. At the end of thenegotiation process, provider and consumer commit to an

agreement[4]. This agreement in the SOA is referred to as aSLA.

SLA is an important protocol and it is a third party between the cloud providers and cloud customers. Manyattributes (such as response time and throughput) can belisted in the SLA and these attributes are mostly different for the different demands. So if we can draft some SLAtemplates according to different services and offer them to

providers or consumers, it will be more equitable to carry outa negotiation and make providers and consumers commit anagreement more conveniently. On the other hand, becausethere are no metrics can be referred, it is difficult for consumers to compare the reliability of cloud providers andhence how to select the most reliable providers becomes agreat challenge. In this paper, we propose a platform of SLAin cloud computing environment in order to help cloudconsumers to select most reliable cloud providers and makenegotiation process more equitable and standardized.

The rest of this paper is organized as follow. We reviewthe related work in section II. In section III, we introduce thearchitecture of our platform proposal. Then we present anentity graph and a proposed protocol to evaluate our platformin section IV. In section V, we summarize our work and

offer the idea for the future work.II. RELATED WORK

There is a wide-range of works around the SLA for cloudcomputing. Some models of cloud computing are introducedto maintain the reliability between cloud providers andconsumers involved in the negotiation process[3,4,6]. Someworks focus on the revenue and Quality of Services (QoS),and then some mechanisms are introduced to maximize thecloud consumers or providers revenue[5,9]. Monitoring incloud is also a hot topic in cloud computing research. Somearchitectures are proposed to improve the capacity of thecloud monitor[16,17].

Mohammed Alhamad et al.[3] present a trust model to

evaluate cloud services, and then a new solution of definingthe reliable criteria for the selection process of cloud

providers is presented. A mechanism for managing SLAs ina cloud computing environment using the Web Service LevelAgreement (WSLA) framework is proposed[4]. In a servicesoriented architecture, it is developed for SLA monitoring andSLA enforcement.

Mohammed et al.[6] proposes a conceptual SLAframework to maintain the trust and reliability between cloud

providers and consumers involved in the negotiation process.

2011 Ninth IEEE International Conference on Dependable, Autonomic and Secure Computing

978-0-7695-4612-4/11 $26.00 2011 IEEEDOI 10.1109/DASC.2011.184

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2011 IEEE Ninth International Conference on Dependable, Autonomic and Secure Computing

978-0-7695-4612-4/11 $26.00 2011 IEEEDOI 10.1109/DASC.2011.184

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2011 IEEE Ninth International Conference on Dependable, Autonomic and Secure Computing

978-0-7695-4612-4/11 $26.00 2011 IEEEDOI 10.1109/DASC.2011.184

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In the paper, the author proposes the different metrics in theSLAs for different cloud services (such as IaaS and SaaS)and introduces the negotiation strategies.

Mario et al.[5] introduces several business rules for maximising the providers revenue and proposed anintermediate entity, called Economically Enhanced ResourceManager (EERM). If cloud providers are not able fulfill all

the SLAs that have agreed, the EERM can select some SLAswhich are estimated to be less losing according to the next

process to be violated or canceled. However, some rules(such as Selective SLA Violation and Selective SLACancellation) may make the providers loss their reputations.

Comuzzi et al.[16] focus on the relationship betweenestablishment and monitoring. The author also proposes anarchitecture for monitoring SLAs. In this architecture, twomain requirements introduced by SLA establishment aresatisfied: the availability of historical data for evaluatingSLA offers and the assessment of the capability to monitor the terms in a SLA offer.

III. ARCHITECTURE

In this section, we introduce our platform of SLA indetails. Firstly, we present the platform architecture in figure1.

Figure 1. Architecture of platform

In this architecture, the platform is the third party between the cloud providers and consumers. Cloud providerscan advertise their services in the platform and cloudconsumers can search and select the services in the servicelist. When the consumers find the services which meet their needs, they can make a negotiation with the providersthrough the platform.

In the figure 1, we know this platform consists of four parties, SLA Template Pool, Reputation System, AlternativeServices and Monitoring Centre. The Monitoring Centre is to

monitor the providers and consumers activities, the qualityof services and the parameters in the SLA documents. In therest of this section, we describe SLA Template Pool,Reputation System and Alternative Services in details.

A. SLA Template Pool The performance of the SLA Template Pool is offering

the SLA templates to the cloud providers and consumers.These SLA templates can be referred by providers or consumers to draft a new SLA document which is moreadaptable to the current services. Moreover, providers or consumers can add these new SLA templates into the SLATemplate Pool and so the new templates can be referred bythe other providers or consumers.

For each SLA template in the SLA Template Pool, thereare some records which include its used times and commentswhich the users make. With the records and comments, the

providers or consumers can make more excellent decisionson the selection of SLA templates. Moreover, with thecontinual application and modification of SLA templates inthe SLA Template Pool, the SLA content for each cloud

service becomes more reasonable, thus it is more equitable,transparent and convenient for providers and consumers toconduct the SLA negotiation.

B. Reputation SystemWith the development of cloud computing, there are

more cloud providers emerge. Though the increase of cloud providers extends consumers range of choice on providers,it also brings some difficulties to consumers in selecting themost reliable providers. We can distinguish the better one

between two providers through their reputations, but we cannot know the reliability of these reputations which providerslist. In the platform, we propose a Reputation System toaddress this challenge.

The Reputation System in the platform not only recordsthe providers reputations, but also it records the consumers.For consumers, they can evaluate and make comments on the

providers according to the quality of services. For providers,they also can evaluate and make comments on the consumersaccording to their performance in the transaction. The itemsin providers reputations that consumers can evaluate qualityof service, attitude of service and credit of transaction. Inconsumers reputations, there is one item that providers canevaluate is the credit of transaction. When the providers or consumers submit the evaluated scores, the calculationmodule in the Reputation System will record these scoresand calculate the value of reputation.

The reputations that Reputation System presents are based on the data which large numbers of users (cloud providers and consumers) offer, so it has a high reliability.But it is possible for some users to cheat so that they canhave higher reputations. In this situation, the reliability of reputations will be affected. In order to solve this problem,we introduce IP Monitor mechanism and Iterance Monitor mechanism.

When the users (cloud providers and consumers) log in,the IP Monitor mechanism records each IP address, and thenmakes an analysis (such as IP region and IP records) on each

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one. After the users submit the scores or comments, theReputation System validates each score or comment usingthe Iterance Monitor mechanism. The Iterance Monitor mechanism checks the IP region, IP records and Transactionvalidity to determine whether the score or comment is validor not. If a score or comment is treated as invalid, theReputation System will record this issue as a dishonest

behavior and send a warning to the submitter. If the counteddishonest behaviors are greater than a threshold, thesubmitter will be punished by the Reputation System.

C. Alternative ServicesFor the users (cloud providers and consumers) who have

higher demands in services, the basic services are not enoughto meet their demands, so some extra services is needed for them to achieve their goal. In the platform, we proposeAlternative Services to provide these extra services for usersand so the users can acquire these services by paying extramoney. The Alternative Services include three services:Management Services, Measurement Services and ExternalInterface.

1) Management Services: Management Services is provided for cloud providers. The Management Servicesincludes three services: selective SLA violation, resourceoverprovisioning and redistribution estimation.

Recent studies[5] present some rules which canmaximize the providers revenue. When the provider is notable to fulfill all the SLAs that has agreed, the selective SLAviolation can perform a selective violation of some SLAs inorder to minimize the economic impact of the penalties[7].The right SLAs which should be violated are chosenaccording to the future profit and penalties that are estimated.Selective SLA violation sometimes affects providersreputations, so the providers can make decision whether theymake use of these rules.

In some situation, idle resources are not enough todistribute to the consumers, and so the providers will refusethe SLA proposal from the consumers. However, theconsumers do not always use the total resources they havereserved and hence these unused resources could be to other clients for increase the revenue. The performance of resourceoverprovisioning is to finish this work.

The performance of redistribution estimation is to look for the tasks that are underutilizing their resources. If thereare enough underutilized resources, a sufficient portion of them will be unassigned from their current tasks, andassigned to the task with insufficient resources. This processis easy to implement thanks to Virtualization technology [8].

2) Measurement Services: Measurement Services is provided for cloud consumers. The Measurement Servicesincludes three services: quality measurement, cost/pricemeasurement and usage measurement.

Quality measurement is to measure the quality of services and it provides measurement result for theconsumers. There are two kinds of measurement results. Thefirst is the raw data which is not processed or calculated, andthe other one is the composite data which has been processedor calculated according to some common method.

Cost/price measurement is used to measure the currentcost/price when the billing methods or price of providers isthe dynamic. Usage measurement is to measure the currentusage of the consumers. According to the information

presented by cost/price measurement and usagemeasurement, consumers can know more about the services.

3) External Interface: If the users (cloud providers andconsumers) consider the services that the platform offers stillcan not meet their demands or they want the other serviceagencies to offer the better services (such as measurementservices and monitor services), they can connect the other service agencies using the External Interface.

IV. EVALUATIONIn this section, we evaluate our platform in two aspects.

Firstly, we present the platform entity-relationship graph infigure 2.

Figure 2. Entity-relationship Graph

From the figure 2, we know the amount of entities in the platform and the relationship between them. Then weevaluate our platform in another aspect, a proposed protocol.The protocol is listed as follow.

A. Advertise the servicesCloud providers can register or login after they enter into

the platform. At the same time, the Reputation Systemrecords the IP address. Then providers can add the servicesinto their service list and submit it to the platform. The

platform will list the providers, their service and their reputations in a public area.

B. Search the servicesAfter registering or login, Cloud consumers can search

the services or providers by search engine in the platformand sort the search results according to their demands (suchas reputation and price). For example, if the consumers careabout the reputation more than the price, they can sort theresults by the providers reputation from high to low, and if

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they care about the price more than the reputation, they cansort the results by the price. It is more feasible for theconsumers to compare and select than the traditional ways,and so they can find more suitable services and providers.After the consumers finish selecting, they can contact the

providers and conduct a SLA negotiation.

C.

Conduct negotiation processIn the negotiation process, the consumers and providersneed to sign a SLA document. SLA templates can beacquired from the SLA template pool and each template hasa used times record and comments. So in the draft process,the providers or consumers can refer the suitable SLAtemplates which are selected according to used times recordsand comments of each template, and then to draft SLAdocuments. For example, if a cloud consumer needs tonegotiate with a cloud provider, but he doesnt know whatmetrics should be listed in the SLA document. In thissituation, he can select the suitable template from the SLAtemplate pool to refer and then he can draft a morereasonable SLA document. Through the SLA template pool,

it becomes more feasible for users (cloud providers andconsumers) to draft a SLA document. Comparing with someSLA documents which are drafted without the SLA template

pool, the SLA documents which are drafted with the SLAtemplate pool are more reasonable.

D. Select Alternative ServicesIn the SLA negotiation, the providers and consumers can

select some alternative services if they have higher requirements. For example, if a provider needs to provideservices for eight consumers and can not fulfill all SLAs hasagreed, he can select Selective SLA Violation services tomaximize his revenue. Particularly, if the consumers needthe other entities to offer some extra services, they shouldselect the External Interface services before the SLAnegotiation and list this item in the SLA document.Alternative services can improve the QoS and the consumersand providers revenue.

E. Evaluate and make commentsWhen the transactions are finished or canceled, the

providers and consumers must evaluate each other. Whenthey finish evaluating and submit the scores, the reputationsystem will calculate the lastest value of their reputations.After evaluating, the consumers and providers must makecomments on each other. Evaluating and making commentsare two important key parts in the platform. Due to theReputation System, the reputation of the users has higher reliability, so the SLA negotiations become more equitablethan the traditional ways and the QoS is improved.

V. CONCLUSIONS AND FUTURE WORK Due to no metrics can be referenced, the increase of

cloud providers bring difficulties to cloud consumers incomparing and choosing providers. In order to address thischallenge, we present a conceptual platform of service levelagreements in this paper. In section III, we describe thearchitecture of this platform particularly. In its architecture, it

consists of four parties and the Reputation System is theessential party. By comparing their reputations andcomments which the Reputation System has recorded, theconsumers can select the most reliable providers. Moreover,the reputations have higher reliability because they are basedon the large amount of data which the users offer. Not onlythe Reputation System make it is easier for consumers to

choose the providers, but also the SLA Templates Pool in the platform makes the negotiation process more equitable. For some users have higher demands, the Alternative Services inthe platform can meet their needs.

In this paper, we mainly discuss on the architecture of the platform. In the future work, we plan to investigate thefollowing:

According to the architecture we have proposed,implement a simulation experiment to test our

platform in the cloud computing environment. Doing a further research on the dynamic price or

billing model which is adapted to the elasticstructure of cloud program.

VI. ACKNOEWLEDGEMENT This work is supported by the project of the Science and

Technology Commission of Shanghai Municipality:10510500600, by Shanghai Leading Academic DisciplineProject [J50103].

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a conceptual platform of sla in cloud computing

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