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WS-Agreement in AssessGrid James Padgett Collaborative Architectures and Performance Group

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1 WS-Agreement in AssessGrid James Padgett Collaborative Architectures and Performance Group

2 Best Effort resource provision is not a motivator for Grid commercialisation Ownership and use of Grid resources has economic value since resource owners may choose to charge rather than freely share and provision their resources. Service Level Agreements (SLAs) provide one artefact to enable Grid commercialisation Agreeing an SLA is a business risk for both a consumer and provider Agreements on resource provisioning may not only include the providers commitment to execute a task or provide the resources but also include terms about performance levels and penalties (provisioning).

3 AssessGrid Actors End-users approach the Grid in order to perform specific tasks. In order that their task is completed, they negotiate access to resources using SLA requests The broker acts as a matchmaker between the end-users and providers, providing a time/cost/risk optimised assignment of SLA requests to SLA offers. Providers offer access to resources through formal SLA offers specifying risk, price and penalty. Providers need well-balanced infrastructures, so they can maximise the Quality of Service and minimise the number of SLA violations.

4 AssessGrid System Architecture End-user –Portal Broker –Risk Assessor –Confidence Service –Workflow Assessor Provider –Negotiator –Scheduler –Risk Assessor –Consultant Service

5 AssessGrid Usage Scenario Broker negotiates on behalf of the end-user SLA are negotiated using WS-Agreement (WS-A) Grid middleware and Grid fabric enhanced with risk assessment and data service –Confidence service –Consultant service Risk assessment based on historical data returns ranked list of SLA offers with adjusted risk

6 AssessGrid SLA Offers Published risk enables End-users to compare different SLA offers –Risk of failure, price, and penalty fee Brokers Reliability measure classifies which offers are reliable

7 WS-Agreement SLA Structure Guarantee Terms describe aspects of the agreement which the parties are contractually obliged to uphold – often they reference the SDTs Service Description Terms (SDT) describe the requirements of the agreement The terms are made up of those which describe the service offering and the active guarantees Context defines key facts about the agreement like the agreement initiator / responder and the service provider – they can be different Name identifies the SLA SLAs state the terms of agreements between a consumer and provider as a contract for the provider to perform a service or to provide agreed resources.

8 AssessGrid SLA Template

9 Problems along the way... Globus Based on Axis 1, unable to support WS- Agreement: –substitutionGroup (see next slide) WSA – implemented using dated WS- Addressing spec, therefore cant talk to other major WS-Agreement implementation WSAG4J WSRF – implemented using non-standard spec

10 ...problemantic content Provides: xs:minExclusive, xs:minInclusive, … Provides: xs:all, xs:choice, xs:sequence…

11 ...the solution

12 Related Work AssessGrid – WS-Agreement – Globus – WSAG4J: – project/wsag4j/index.html project/wsag4j/index.html IBM Cremona – /cremona/README.htm /cremona/README.htm

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