WS-Agreement in AssessGridWS-Agreement in AssessGrid

James Padgett

Collaborative Architectures and Performance Group

jamesp@comp.leeds.ac.uk

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 riskfor both a consumer and provider

• Agreements on resource provisioning may not only include the provider’s commitment to execute a task or provide the resources but also include terms about performance levels and penalties (provisioning).

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.

AssessGrid System Architecture

• End-user– Portal

• Broker– Risk Assessor– Confidence Service– Workflow Assessor

• Provider– Negotiator– Scheduler– Risk Assessor– Consultant Service

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

AssessGrid SLA Offers

• Published risk enables End-users to compare different SLA offers– Risk of failure, price, and penalty fee

• Broker’s Reliability measure classifies which offers are reliable

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.

Agreement

Name

Context

Terms

Service Description Terms

Guarantee Terms

AssessGrid SLA Template

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 can‘t talk to other major WS-Agreement implementation WSAG4J

• WSRF – implemented using non-standard spec

...problemantic content

<xs:complexType name="OfferItemType"><xs:sequence>

<xs:element ref="wsag:Location" /><xs:element name="ItemConstraint">

<xs:complexType><xs:choice minOccurs="0">

<xs:group ref="xs:simpleRestrictionModel" />

<xs:group ref="xs:typeDefParticle" /></xs:choice>

</xs:complexType></xs:element><xs:any processContents="lax" minOccurs="0"

maxOccurs="unbounded" /></xs:sequence><xs:attribute name="Name" type="xs:string" />

</xs:complexType>

Provides:xs:minExclusive,xs:minInclusive, …

Provides:xs:all, xs:choice,xs:sequence…

...the solution

<xs:complexType name="OfferItemType"><xs:sequence>

<xs:element ref="wsag:Location" /><xs:element name="ItemConstraint">

<xs:complexType><xs:any/>

</xs:complexType></xs:element><xs:any processContents="lax" minOccurs="0"

maxOccurs="unbounded" /></xs:sequence><xs:attribute name="Name" type="xs:string" />

</xs:complexType>

Related Work

• AssessGrid– www.assessgrid.eu

• WS-Agreement– http://forge.gridforum.org/projects/graap-wg

• Globus– www.globus.org

• WSAG4J: – http://packcs-e0.scai.fraunhofer.de/mss-project/wsag4j/in

dex.html

• IBM Cremona– http

://awwebx04.alphaworks.ibm.com/ettk/demos/wstkdoc/cremona/README.htm