Negotiation In Cloud During Service Level Agreement - A Survey.

Transcription

1 Negotiation In Cloud During Service Level Agreement - A Survey. A B S T R A C T Lissy A* 1, Debajyoti Mukhopadhyay 2 1, 2 Maharashtra Institute of Technology, Pune University [email protected] Cloud Computing provides cheap and subscription based access to computing and storages services over the internet. In cloud computing, it remains a challenge to allocate resource with financial cost minimization and acceptable Quality of Service assurance. The negotiation is the way of communication to prepare an agreement for accessing the cloud resources. As more and more consumers delegate their tasks to cloud providers, Service Level Agreements (SLA) between consumers and providers emerge as a key aspect. The SLA is negotiated between client and a provider for executing the job on computing resources. There are various negotiation models that have been proven to satisfy both the provider and the consumer. The provider s satisfaction consists in maximizing the profit and utilization, while the consumer s satisfaction is based on the price going to be paid along with Quality of Service (QoS). Index Terms: Cloud Computing, SLA Negotiation, Negotiation Strategy, Agent Negotiation, Negotiation Protocol I. INTRODUCTION Cloud computing [1] is the new trend of computing where readily available computing resources are exposed as a service. These computing resources are generally ordered as pay-as-you-go plans and hence have become attractive to cost conscious customers. We see a growing trend of off-loading the previously in-house service systems to the cloud, based primarily on the cost and the maintenance burden. Such a move allows businesses to focus on their core competencies and not burden themselves with other operations. Intelligently managing and allocating resources among various customers in a cost-effective manner is important for service providers. An SLA (Service Level Agreement) [1] plays a main role in resource provisioning. Cloud SLA Negotiation is a process of joint decision making between Cloud users and to resolve conflicting objectives. A service-level agreement is a negotiated agreement among two parties, where one is the consumer and the other is the service provider. This can be an officially required formal or an informal contract. In this paper SLA defines a set of quality of service (QoS) constraints such as price, time and task and specifies how the services are accessed by consumer through negotiation. SLA has motivated research and development into formulating, negotiating and establishing such agreements between providers and users. Many grid systems have also incorporated SLA specification, exchange and monitoring capabilities for resource brokering and task scheduling and for resource provisioning.service deployment [2] in cloud can be considered as a process containing following steps as shown in Fig. 1. During the Service Discovery phase, user requirements are used as an input for discovering the best suited Cloud Services among various repositories of Cloud provider s.in the SLA , IJAFRC All Rights Reserved

2 Negotiation phase, discovered providers and the use negotiate on the quality of services. Next, SLA contract will be achieved if two parties reach an agreement on a set of QoS values. Then, the acquired service will be continuously monitored in the Monitoring phase. In the Decommissioning phase after the use the services are terminated. All the above phases mentioned Service, Discovery, Monitoring and Decommission are automated; hence there is a need for the SLA Negotiation phase also to be automated to avoid the bottleneck and make the deployment faster. II. PRICING PLANS Figure 1: Service Deployment Phases The following pricing plans can be taken into consideration. A. Fixed recurring pricing The users can set up a plan where they can have the same amount of resources every month. This is similar to the contract plans available today in cloud computing. B. Variable pricing by resource consumption In this case the price can vary based on how many resources there are used at a time. This has been adjusted for the on-demand plan where the users are paying based on how many resources they need. C. Variable pricing by time The price varies based on how much time the client uses the resources for. Longer the duration of the usage lesser the price that is offered for. This has been implemented in the spot pricing provided by Amazon. D. Cost multipliers This help the providers increase the price by a factor. This has not been implemented in any of the cloud computing pricing schemes. They are mostly used by insurance companies. III. NEGOTIATION PRICING In the following part, we are going to describe different types of pricing which allows basic negotiation between the consumer and the provider. The providers whom we have taken into account are Amazon and Microsoft Azure , IJAFRC All Rights Reserved

3 A. On-Demand Instances International Journal of Advance Foundation and Research in Computer (IJAFRC) On-demand allows users to pay for as much as they use without any long-term commitment. This allows the user to rent and maintain hardware at a low cost. However, Amazon charges by the hour, even though a consumer used only one and a half hours, he/she will still be charged for the two full hours. This type of pricing is mostly used for applications that require short computations. In case users need to run the application for a very long period of time such as a year, he/she will be better off by choosing a long-term commitment. This has been proven to be cheaper than using on-demand pricing for a full year. The pricing for each instance in this case is set according to the complexity of the instance. The instances that do not involve GPUs or lots of CPUs will be automatically cheaper since they are mostly used for simple development and not for high performance, but at the same time resources which are highly demand on the market will be charged more as there are many consumers who are willing to use the service. B. Spot Pricing Instances Spot pricing allows instances, the user has to bid the biggest price he/she is willing to pay in order to run the instances users to reserve for a period of time the unused space in the cloud at a much lower rate than the on-demand pricing. When using spot pricing. C. Reserved Instances This pricing model provides long-term commitment. This is for users to ensure their resources at anytime they want. Using a contract gives a user the benefit that those resources will be there at all times as well as saving a great deal of money. So by doing a long-term commitment users get a lower rate for the instances they want to use. IV. NEGOTIATION PROTOCOL The negotiation protocol refers to a set of rules, steps or sequences during the negotiation process, aiming at SLA establishment. It covers the negotiation status (propose offer, accept/reject offer, and terminate negotiation), which can be updated during the negotiation process. It is common to characterize negotiations by their settings: bilateral, one-to-many, or many-to-many [2]. A. Bilateral Negotiation In this two agents have a common interest in cooperation, but have conflicting interests regarding the particular way of doing so. Hence negotiation happens between them till they arrive at a conclusion as shown in Figure 2. Figure 2: Bilateral Negotiation , IJAFRC All Rights Reserved

4 B. One-to-Many Negotiation International Journal of Advance Foundation and Research in Computer (IJAFRC) In this we are tackling is one in which one agent (buyer or seller) wants to negotiate a deal with a number of opponents, in order to find the best possible deal in the market. The consumer can bargain parallel with multiple service providers till the desired value is obtained (Figure 3).Single or multiple negotiation rounds can happen between the consumer and providers till the time or expired or negotiation is successful. Figure 3: One-to-Many Negotiation C. Many-to- Many Negotiations In this multiple issues are negotiated among agents, where a win-win solution is possible. However, a multi-attribute negotiation is more complex and challenging than a single-attribute one, because of complex preferences over multiple issues and the multiple-dimensional solution space as in Figure 4. Figure 4: Many-to-Many Negotiation V. NEGOTIATING STYLES There are many styles of negotiating [5]; the more common among them are competing, collaborating, compromising, avoiding, and accommodating. Each style has its advantages and disadvantages, and it is crucial to be tactical in which style you choose, considering such factors as the style of the other Negotiator And The Type Of Negotiation. A. Competing Style It is the most adversarial style. Negotiators who gravitate to this style see negotiations as competitions that have winners and losers. The other negotiation styles see competing negotiators as aggressive and strategic. The competing style works best when you need a fast negotiation or when there aren't many , IJAFRC All Rights Reserved

5 variables at play, such as simply negotiating over the price of a product. However, the competing style does not work well when used against another using the competing style; often, deadlock occurs, and relationships become frayed or even hostile. B. Accommodative Style It is a submissive style. Accommodators are ready and willing to give information and to make concessions. Accommodators often let the other side of the table win on issues. This can be dangerous when negotiating against a competing style. However, accommodators put relationship as a top priority, and this style can be very successful in negotiations in which mending or maintaining relationships is critical. For example, if your company is in the midst of a crisis, an accommodative strategy can be very successful at avoiding litigation and appeasing the other party. However, unless the situation involves a relationship crisis, use accommodative strategies sparingly - giving away too many concessions or too much information in a negotiation might lead to a less than ideal outcome. C. Avoiding Style It is passive aggressive and tends to skirt issues rather than confront them head on. Avoiders tend to come across as less transparent and honest, and lines of communication can be weak. Often times, this style is employed by negotiators who do not respond well to conflict or aggression. Rather than make accommodations, the avoiders simply avoid the situation. With that said, an avoiding style has its advantages in a highly emotional negotiation. Avoiders can avoid confronting emotions and passions and instead focus on hard numbers in order to reach an agreement. The avoiding style also works fine when the negotiation is simple or trivial. However, due to looming communication issues, the avoiding style has the ability to result in deadlock and resentment, as well as strained relationships. D. Compromising Style It involves meeting halfway. One side makes some concessions, while the other side makes some concessions. In the end, there are no clear winners, but rather, what is believed to be a fair result instead occurs. Parties tend to start out at extreme positions, then work their way to the middle. This style is used often in positional bargaining. It works well when there are time constraints or there is an ongoing and strong relationship with the other party. While this format helps keep relationships strong, the agreements are usually not the most optimal agreements for both parties. E. Collaborating Style It involves ensuring that both parties' needs are met. Parties brainstorm on how to create mutual value and think outside of the box on collaborating on a solution. Collaborating is all about value creation and is commonly encouraged by those who support the principled negotiation format. Collaborators expand the pie and strive to meet an optimal agreement that maximizes everyone's returns. This style is great at forming strong bonds or maintaining good relationships. However, the collaborating style is the most consuming style and the most mentally exhausting style. It also requires the most preparation. In addition, it does not work as well with competing style negotiators as they may try to take advantage of the situation. VI. NEGOTIATING STRATEGIES , IJAFRC All Rights Reserved

6 There are many negotiation strategies used in cloud services; we will be discussing about Concession Strategy [7], Tradeoff Strategy [7] and Confronting in detail. A. Utility Functions In economics, a utility function measures the level of satisfaction a consumer receives from any basket of goods and services [6]. It is adopted here to measure the level of satisfaction that users receive from Cloud services. For an attribute whose utility changes linearly with its value, a linear function can be used to calculate its utility. Let x be such an attribute, xbest its best value, and xworst its worst value. Its utility, u1(x), can be calculated by x xworst u1( x) = x x best Where 0 u1(x) 1, u1 (xbest) =1 and u1 (xworst) = 0. It should be noted that xbest and xworst are defined by negotiation gents on their own account. In particular, when x is higher-is-better attribute, xbest>xworst, and when x is lower-is-better one, xbest<xworst. After that, a weighted sum function can be used to calculate the total utility of a proposal, p, containing n attributes that are additive by n worst u ( p) = wi. u1( x ) 2 i i= 1 Where wi is the weight of attribute xi (i= 1 to n), i= B. Tradeoff Strategies n w i 1 = 1. The key point of tradeoff strategies is that, in preparing a counter proposal, the total utility of a reference proposal remains the same for one party, but the values of some of its attributes are adjusted in favor of the other party. If, for this reason, the utility of one attribute is decreased by a certain amount and that of another increased by the same amount, the total utility may not change for the first party. Even so, this strategy can encourage the second party to accept the counter proposal, since its utility is increased in this case. It should be noted that either a proposal preferred by one party or one received from the other party can be set as the reference proposal; however, the choice matters in that it may affect the utility the first party can gain. Xianrong Zheng, Patrick Martin and Kathryn Brohman offered two algorithms, which we have included without any modification for the sake of explaining negotiation strategies [7]. Algorithm 1 works as follows. First of all, in line 1, agent isend V as a proposal to agent j and waits for a response. If agent j does not accept V and its counter proposal is not acceptable to agent i, tradeoff is used by agent i in the while loop of lines 2-23 to create a new proposal; otherwise, true is returned in line 24. Here, the acceptance criterion is that the utility received is no less than that of their respective reserved proposal. Next, in line 4, k is increased by one each time the while loop repeats. In lines 5-6, function calculateutilitycalculates the utilities u0 and u1 of agent i s values V [0] and V [1], respectively. In line 7, function aggreateutilitycalculates the total utility usumof agent i s preferred proposal V. In fact, the two functions implement the linear function and the weighted sum function in Equations 2 and 3, respectively. After that, in lines 8-13, if weights W [0] < W [1], u0 is reduced by and u1 thus becomes usum u0; otherwise, u1 is reduced by and u0 becomes usum u1. In both cases, it ensures that agent i s important attribute creates more utility , IJAFRC All Rights Reserved

7 Finally, in lines 14-18, if u0 <0 or u1 <0, no values for V [0] or V [1] can be found, then tradeoff fails; otherwise, the new values can be found by function restorevalue, which is the inverse function of Equation 2. In lines 19-22, if V is out of bounds, false is returned; otherwise, agent isends V whose values are adjusted but its utility remains the same for itself to agent j as a new proposal, and waits for a response. The process repeats until success or failure occurs. It should be mentioned that since u0 (or u1) is reduced by each time the while loop repeats, Algorithm 1 converges and terminates.[(ג/ O[(1, rounds [ג where. In other words, it s running time can be bounded as [1/ within C. Concession Strategies The main idea of concession strategies is that, in preparing a counter proposal, the total utility of a reference proposal is reduced for one party, and, accordingly, the values of some of its attributes are adjusted to favor the other party. Indeed, to stimulate the other party to accept the counter proposal, a certain amount of utility is deducted from the reference proposal, when one party makes a concession. It should be mentioned that, either a proposal preferred by one party or one received from the other party can be set as the reference proposal, but the choice matters, as it may affect the utility the first party can gain. Concession strategies have been used to acquire web. When something unfavorable happens, for instance, the deadline approaches, concession strategies can be applied. Algorithm 2, which differs with Algorithm 1 in lines Here, each time the while loop repeats, u0 is reduced by in lines 7-8. Also, the acceptance criterion is that the utility received is no less than that of one s reserved proposal. However, when one serves as the offer and makes a concession, its utility is allowed to be less than its reserved utility , IJAFRC All Rights Reserved

8 D. Confronting In this strategy the negotiator participant faces the conflict head-on and aims at a solution that is mutually satisfactory. The negotiator strives to find a solution that is acceptable to both the parties. This strategy seeks to maximize the outcomes for both the sides. This strategy is also known as problem solving or integrating. It is a strategy that really seeks a resolution to the conflict. The benefits of the confronting approach are: 1) It is productive since both parties gain. 2) It examines the cause of differences between the two parties and seeks a creative solution of the problem. 3) It aims at a solution that integrates the interests of all concerned parties. 4) It maintains the self-respect of both the parties and creates mutual respect between them. VII. AGENT BASED TESTBED In a Cloud market, there are many consumers and service providers, and thus, the Cloud testbed has consumer agents and provider agents acting on behalf of consumers and providers. The roles of each component in the testbed are given in (Table 1). Cloud service providers and consumers participate in the Cloud market of the testbed[4] through the Cloud registry. All agents participating in the Cloud market are registered in the Cloud registry. All consumer agents connected to the Cloud market registry can then recognize and communicate with each provider agent. Table 1: Roles of Components in Agent Testbed Component Roles Provider Agent Service Provider, Service Advertisement, Service Negotiation Consumer Agent Service Consumer, Service Discovery, Service Negotiation Cloud Registry Agent information repository Provider agents and consumer agents generate service descriptions and specify their preferences with regard to service name, price, time slot, QoS and negotiation strategy based on a GUI. For Cloud service reservations, the testbed provides simple service discovery functionality through message passing. A consumer agent broadcasts a message indicating the name of the Cloud service that the consumer needs to all provider agents, and a provider agent who has the service replies to the consumer as shown in Figure , IJAFRC All Rights Reserved

9 Figure 5: Agent Based Testbed VIII. CONCLUSION As the cloud market becomes more open and competitive, price and time as well as QoS will be more important. However, cloud providers and cloud consumers have different and sometimes opposite preferences. If such a conflict occurs, a SLA cannot be reached without negotiation, which is considered as the most flexible approach to procure products and services. Various negotiation styles and strategies have been studied and proven productive in terms of cloud service negotiation. Hence based on the circumstances the desired negotiation mechanism can be used to arrive at a win-win situation. Automated negotiation occurs, when software agents negotiate on behalf of their human counterparts to avoid the bottleneck caused by manual negotiation in cloud service deployment. IX. References [1] Seokho Son, Sung Chan Jun, Negotiation -Based Flexible SLA Establishment with SLA-driven Resource Allocation in Cloud Computing, 13thIEEE/ACM International Symposium on Cluster, Cloud, and Grid Computing, Delft, pp ,2013. [2] Amir Vahid Dastjerdi,Rajkumar Buyya, An Autonomous Reliability-aware Negotiation Strategy -Cloud Computing Environments, 12th IEEE/ACM International Symposium on Cluster, Cloud, and Grid Computing,Ottawa, ON, pp ,2012 [3] S. Son and K. M. Sim, A multi-issue negotiation mechanism for Cloud service reservation, Proceedings of the Annual International Conference on Cloud Computing and Virtualization, pp , [4] Gabriela AndreeaMorar, Andreea Ilea, AlexandruButoi, Gheorghe CosminSilaghi, Agent-based cloud resources negotiation, IEEE International Conference on Intelligent Computer Communication and Processing (ICCP), Cluj-Napoca, pp ,2012. [5] Seokho Son, Sung Chan Jun; SLA-based Resource Allocation for Software as a Service Provider (SaaS) in Cloud Computing Environments, 11th IEEE/ACM International Symposium on Cluster, Cloud, and Grid Computing, Newport Beach, CA, pp ,2011. [6] Seokho Son and Kwang Mong Sim; A Price- and-time-slot-negotiation Mechanism for Cloud Service Reservations, IEEE Transactions on Systems, Man, And Cybernetics part b: cybernetics, Vol. 42, No. 3, pp , , IJAFRC All Rights Reserved

10 [7] Xianrong Zheng, Patrick Martin and Kathryn Brohman; Cloud Service Negotiation: Concession vs. Tradeoff Approaches, 12thIEEE/ACM International Symposium on Cluster, Cloud, and Grid Computing, Ottawa, ON, pp , , IJAFRC All Rights Reserved