Enhancing SLA using push/pull Services in Cloud Computing

Enhancing SLA using push/pull Services in Cloud Computing

N. Ani Brown Mary

Software Engineer

Abstract The word Cloud is an acronym for Internet. Service Level Agreement is used to negotiate for resources between a consumer and a service provider. SLA is also called as a resources or application contract between consumers and service providers. Since SLA is an important task it has to be considered and evaluated to improve the profit of service providers and consumers. Here we use pull and push services to improve the SLA contract in a efficient way. By using this push and pull services it improves better services and activation in SLA negotiation.

Keywords: SLA, push services, pull services, Cloud computing, negotiation

1. INTRODUCTION

   1200

   1000

   800

   600

   400

   200

   0

   Cloud Consumers

   Worldwide

   processing occurs or where your data are stored. It is also possible for a consumer and the service provider to mutually agree upon a set of SLAs with different .performance and cost structure rather than a single SLA. The consumer has the flexibility to choose any of the agreed SLAs from the available offerings. At runtime, the consumer can switch between the different SLAs. Since SLA is a major task it is used for many purposes in cloud computing.

   Each SLA goes through a sequence of steps starting from identification of consumers and cloud providers, then identifying their terms and conditions, then monitoring their contract and negotiation. The cloud provider manages and offers guarantees on availability of the infrastructure, namely, server machine, power, network connectivity, and so on. Enterprises manage themselves, their applications that are deployed on these server machines. The machines are leased to the consumers and are isolated from machines to other consumers. Cloud providers offers a service-level guarantees to consumers.

   Service provider advertises base service offerings through standard publication media, and the consumers should be able to locate the service provider by searching the catalog. The consumers can search different competitive offerings and shortlist a few that fulfil their requirements for further negotiation. So SLA plays a vital role in Cloud computing. It act as a interface between consumer and service providers. Since we have to put special effects to improve SLAs. In our work push functions are used to structure the Virtual Machines to avoid the unnecessary consumer and service provider interactions.

   2000 2002 2004 2006 2008 2010 2012

   Years

   Figure:1 Cloud Consumers Worldwide in Billions

   An SLA can be described as a contract between participants, outlined as a set of guarantees, QoS metrics and behaviours and should be treated as a legal document of the transaction[1]. More and more consumers are using Cloud services very interestingly.

   Figure:1 shows the increasing consumers to Cloud services worldwide. This figure shows the tremendous growth rates up to 2008. That growth continues today, mainly due to China that has the largest number of consumers.

   Cloud storage offerings are already available from providers located across the globe. The principle of Cloud computing and storage is that you shouldnt need to care where the

2. RELATED WORK

   Consumers in Billions

   Service Level Agreements are very useful to improve profit of service providers. Zhang et.al[5] designed a resource allocation scheduler to maximize the profits of web applications. Here the problem that occurs due to multi-tier SLAs has not been considered. Normally, traditional push services has been used only in mobile computing. But Brenna et.al[6] used push/pull services in information handling. The push functions are used to structure the Internet to avoid the unnecessary client-server interactions dominating the Internet. These functions are also used in banking[19] in an efficient way.

   Morin et al[9] have identified SLA issues and their corresponding challenges, proposing to use risk and Service Level Agreement (SLA) management as the basis for a service level framework to improve governance, risk and compliance

   in cloud computing environments. Stefan et al[10] used an specified SLA to attract companies to outsource their services to clouds. Here providers need to offer consumers using key performance indicators only.

3. SEQUENCE DIAGRAM FOR PUSH SLA

   This sequence diagram shows the relation between the consumers, SAAS, PAAS and IAAS. Service Level Agreements are used have the contract relationship and negotiation between each providers to provide the resources from virtual machines. Indicate new SLA shows the contract or offers that are provided by the service providers to consumers. That is pushed or shown to consumers using push SLA technique. Service Indication technique is very much useful to indicate services that are provided by various providers to consumers. Resources and Services are provided to various consumers depending on their SLA contract.

   The Cloud providers are flexible in allocating and de- allocating computing resources among the co-located applications. Therefore, the cloud providers are also responsible for ensuring to meet their consumers application. It is also possible for a consumer and the cloud provider to mutually agree upon a set of SLAs with different performance and cost structure rather than a single SLA. The consumer has the flexibility to choose any of the agreed SLAs from the available offerings. At runtime, the consumer can switch between various SLAs. SLA displays the response from various consumers to the service providers. Both consumers and providers share their SLA constraints between them.

   Then depending on the SLA constraints the providers provides offer to the consumers. Service provider advertises these base service offerings through standard publication media, and the consumers should be able to locate the service provider by searching the catalog. The consumers can search different competitive offerings and shortlist a few that fulfill their requirements for further negotiation. Individual SLAs for enterprises can be derived by customizing these base SLA templates. Thus this sequence diagram is very much useful to know the interactions between the consumers and the service providers with push SLA services.

   Figure:2 Sequence Diagram for SLA

4. PUSH ARCHITECTURE

   Consumers pulling resources from providers are typical for todays Cloud system. In a push context the service provider initiates the resource transfer, not the consumer. The Infrastructure as a Service provider transfers resource via the Platform as a Service provider to a consumer. The push access controls communication between Infrastructure as a Service provider and Platform as a Service provider. The push over the air is used between the Platform as a Service provider and the consumer. If the Infrastructure as a Service provider is able to use the push OTA, it can directly communicate with the consumer, too.

   Infrastructure as a Service (IaaS)

   Platform as a Service (PaaS)

   Software as a Service (SaaS)

   Push Push

   Providing Resources

   Running,coding, checking

   Consumers, Brokers

   Access

   OTA

   Figure:3 Push Architecture

   The Platform as a Service provider provides many functions to transform SLA agreements and applications exchanged between service provider and consumer. If required, the Platform as a Service provider send success or failure notifications to the Infrastructure as a Service rovider. In Platform as a Service developers can design, build, and test applications that run on the cloud providers infrastructure and then deliver those applications to consumers from the providers servers.

   Push access functions:

   The push access procedure transfers applications from Infrastructure as a Service provider to the Platform as a Service provider. Although push access procedure was developed independently from the underlying delivery service, post procedures are used for transmission. Push access functions offers the following operations:

   Push submission: Delivery of push applications from the Infrastructure as a Service provider to the Platform as a Service provider for forwarding to a consumer. The response indicates the initial acceptance or rejection of the forwarding request.

   Result notification: The Platform as a Service notifies the Infrastructure as a Service so that the result of the push request can be known. With the help of this notification, the virtual server knows if the applications reached the consumer, if the consumer deleted the request, if any penalty occurred at the consumer or if the request arrived too late.

   Push cancellation: The Infrastructure as a Service can try to cancel a push request before delivery to a consumer. The result of the Platform as a Service indicates if the cancellation was successful or not. Cancellation may be used, e.g., for periodic applications buffered at the Platform as a Service because the consumer is currently unavailable. In this case, only the most recent applications may be of interest.

   Status query: With the help of push access procedure, the Infrastructure as a Service provider can query the status of a push resources. The result could indicate, if the Platform as a Service provider already delivered the resources or is still trying to reach the consumer.

   Consumer capabilities query: The Infrastructure as a Service provider might be interested in the consumers capabilities. Additionally, a Platform as a Service provider can inform the Infrastructure as a Service provider about its capabilities regarding resource transformation.

   Push OTA functions:

   The push OTA procedure is a very simple procedure used on Software as a Service. Software as a Service provides a shared state between a consumer and a virtual server to optimize resource transfer. Software as a Service offers general features needed for SLA contract exchange between cooperating consumers and virtual servers. Software as a Service provider introduces sessions that can be established from a consumer to a virtual server and may be long lived. Sessions can also be released in an orderly manner. The capabilities of suspending and resuming a session are important to cloud applications. Consumers and virtual servers can agree upon a common level of procedure

   functionality during session establishment. Example parameters to negotiate are maximum consumer file size, maximum outstanding requests, penalty options, and virtual server speed. Optionally, Software as a Service provider supports a consumer that can send multiple requests to a virtual server simultaneously. This improves efficiency for the requests and provides resources as fast as it possible. Latency is also improved, as each result can be sent to the consumer as soon as it is available.

   The following service primitives have been defined:

   po-push: unacknowledged push of request within a push session;

   po-confirmedpush: acknowledged push of request within a push session;

   po-pushabort: rejection of a push request by the consumer;

   po-unit-push: unacknowledged push of request;

   The following service primitives are also available for push session management:

   pom-connect: creation of a push session by the consumer;

   pom-suspend: suspension of a push session;

   pom-resume: resume of a push session;

   pom-disconnect: termination of a push session;

   pom-sessionrequest: request for a push session by a virtual server;

   A push SLA contract may comprise additional attributes indicating, e.g., the importance or the lifetime of the SLA contract. The following example shows a simple contract offer containing a special pizza, which is only valid for five minutes. If a consumer wants to use this offer, consumer has to request the indicated service via the Software as a Service provider. After five minutes, this push SLA contract will be automatically deleted.

   <?xml version=1.0?>

   <!DOCTYPE si PUBLIC -//WAPFORUM//DTD SI 1.0//EN

   http://www.wapforum.org/DTD/si.dtd>

   <si>

   <indication href=http://www.piiiizza4u.de/offer/salad.wml created=2002-10-30T17:45:32Z

   si-expires=2002-10-30T17:50:31Z>

   salad special: The 5 minute offer

   </indication>

   </si>

   Another variant of delayed service usage can be described using service loading. In this case, the Infrastructure as a Service also sends a short push contract to the consumer. In contrast to service loading, the consumers broker decides when to submit the request, i.e., using the service. Although the service is accessed using a traditional pull scheme it looks for the consumer like a push service. The consumer does not notice the delay between the arrival of the push service and the pull. A disadvantage of service loading is the higher number of requests sent over the Cloud. The following example shows how a Infrastructure as a Service send a push contract to the consumer. No interaction with a consumer is intended.

   <?xml version=1.0?>

   <!DOCTYPE sl PUBLIC -//WAPFORUM//DTD SL 1.0//EN

   http://www.wapforum.org/DTD/s1.dtd>

   <sl> href=http://www.piiiizza4u.de/offer/salad.wml>

   </sl>

5. CONCLUSION

We think that although preliminary and ambitious, this work in progress addresses a critical issue in the growing domain of accountable and trustworthy cloud computing. In this context, push and pull services are an attempt to bridge a gap between the mobile computing and management levels of cloud computing.

The main contribution of this paper is a statement and discussion based on push/pull services in SLA. We propose as contributing elements towards the design of a service level cloud computing SLA push management framework. The planed framework will be organized around interrelated themes such as push function management coupled with SLA and push management.

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