An Application of Dynamic Service Level Agreements in a Risk-Aware Grid Environment

Sanaa Sharaf and Karim Djemame

School of Computing

University of Leeds

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Grid Quality of ServiceGrid Quality of Service

• Grid based systems provide application toolsets which execute on Grid resources.

• Are based on best-effort approach- Resources can be of variable quality and reliability,

particularly when demand is high- No guarantees that the execution of applications will

succeed without errors• Large number of requests for Grid services may lead to a

dramatic degradation in Grid performance and efficiency.• Solution is to define a set of mechanisms that enable service

providers to partition their services based on quality criteria- Priority, fairness, and reliability- Need for Quality of Service (QoS) mechanisms

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Service Level Agreement

• Specifies number/quality of resources over certain time mandatory to reach desired performance- Delegation of particular resource capabilities over a defined time

interval from resource owner to requestor

- SLA as explicit statement of expectations and obligations in a business relationship between service provider and customer

Se

rvic

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Terms R-Type: HW, OS, Compiler, Software Packages, …R-Quantity: Number CPUs, main memory, …R-Quality: CPU>2GHz, Network Bandwidth, … Deadline: Date, Time,…Policies: Demands on Security and Privacy, …

Price for Resource Consumption (fulfilled SLA)Penalty Fee in case of SLA violation

Contract Parties, Responsible Persons

ID or Description of SLAName

Context

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Agreement

Terms Compositor

Service Terms

Guarantee Terms

Context

Name

Information about Service Levels which should be Guaranteed・ optional condition that must be met (when specified) for a guarantee to be enforced・ ServiceLevelQbjective: the condition that must be met to satisfy the guarantee

Information about the Service being provided ・ Contents are Domain Dependent・ E.g..: Job Description (Program name, Number of CPUs etc)

Information about the Agreement Document・ AgreementInitiator・ AgreementResponder・ ExpirationTime

WS-Agreement Structure (GRAAP-WG, OGF)

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Limitations of WS-Agreement

• The main limitation of WS-Agreement is that of being short in supporting negotiation:

1. Only two types of messages: offer and agree. The agreement initiator sends the offer and the responder either accepts or rejects it without any possible way to negotiate.

2. The lack of an interaction protocol between two parties, as a result of having a simple take it or leave it protocol

Agreement Initiator Agreement Responder Agreement Initiator Agreement Responder

Create an offer Create an offer

Agree Refuse

EPR to the agreement

CreateAgreement(offer) CreateAgreement(offer)

Return fault

Templates Templates

GetResourceProperty GetResourceProperty

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Towards Dynamic SLAs

• There are a number of use cases where a more sophisticated process for negotiation is required to reach an SLA- SLA has to be modified to adopt both to changing

requirements from the customer or changing capabilities of a service provider

• Vision about Dynamic SLAs- During run time both parties have the right to hold

the execution under specific conditions and renegotiate to alter the existing SLA

- After renegotiation an altered SLA will possibly be issued and execution will resume.

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Dynamic SLAs - Extending WS-Agreement

• Anticipate violations - state for the agreement in which a warning has been issued

due to the fact that one or more guarantees are likely to be violated in the near future.

• Negotiation- Is part of its life-cycle

- initial negotiation before the execution of the services under SLA

- run-time re-negotiation: occurs in case of • a recoverable violation of a term, or

• the monitoring system is anticipating a possible violation of a term (pessimistic scenario)

• the monitoring system is anticipating a better QoS to be delivered

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Current Agreement state machine

Extending WS-Agreement

Rejected

Observed And

TerminatingPending andTerminating

Pending

Observed

Terminated

Complete

Modified

Offer Received

Proposed Agreement state machine

Rejected

Observed and

TerminatingPending andTerminating

Pending Observed

Terminated

Complete

Offer Received

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AssessGrid: Risk-aware Broker and Provider(s)

End user Broker

Provider

Reliable and trustworthy Reliable and trustworthy Grid provider?Grid provider?

Reliable services for Reliable services for workflow mapping?workflow mapping?

Improve efficiency, reliability, and trust to attract Grid users? Improve efficiency, reliability, and trust to attract Grid users?

Grid resourcesWhat is the risk of assigning an SLA?What is the risk of assigning an SLA?

What is the risk of accepting an SLA?What is the risk of accepting an SLA?

AssessGrid: Advanced Risk Assessment & Management for Trustable Grids

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AssessGrid: Architectural Overview

RMS: Resource Management System

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Building on AssessGrid WS-Agreement Extensions

• Changed the original single-round acceptance model to a two-phase acceptance model• Introduced the negotiation possibility, in other words the bargaining capability:

- Flexible SLA negotiation scheme – getQuotes method- Two-phase commit negotiation protocol

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Customer Provider

I can do X instead of Y for youfor Z in return? SLASLA

Need to ensure both parties get a better deal through the new agreement

Request to re-negotiate

AcceptReject

Example: provider anticipating a possible violation of a term- monitoring of dynamic risk- re-negotiate the SLA instead of paying a (high) penalty fee lower price

SLA Re-Negotiation (pessimistic scenario)

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Customer Provider

Can youdo X for mefor Y in return? SLASLA

Need to define specific properties in the agreement:Re-negotiation needs an EPR

Request to re-negotiate

SLA-AcceptSLA-Reject

Example: user would like to increase the price to get a lower Probaility of Failure

SLA Re-Negotiation (optimistic scenario)

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Customer Provider

I can do X for youfor Y in return? SLASLA

Need to ensure both parties get a better deal through the new agreement

Request to re-negotiate

AcceptReject

Example: provider is able to provide a better service- increase the price- lower Probability of Failure

SLA Re-Negotiation (optimistic scenario)

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Summary & References

• Summary- Need for dynamic Grid SLAs as static SLAs are too rigid.- Need to extend WS-Agreement to support dynamic SLAs- AssessGrid architecture provides a framework for supporting risk

assessment and management throughout the Grid infrastructure - Use as much as possible of WS-Agreement specification- AssessGrid scenarios identified to evaluate future dynamic SLAs

framework

• References1. Djemame, K., I. Gourlay, J. Padgett, G. Birkenheuer, M. Hovestadt, O. Kao, and K. Voß.

Introducing Risk Management into the Grid. in Proceedings of the 2nd IEEE International Conference on e-Science and Grid Computing (e-Science'06). 2006. Amsterdam, Netherlands: IEEE Computer Society: p. 28.

2. Andrieux, A., K. Czajkowski, A. Dan, K. Keahey, H. Ludwig, J. Pruyne, J. Rofrano, S. Tuecke, and M. Xu. Web Services Agreement Specification (WS-Agreement), 2007. Open Grid Forum

3. Battré, D., O. Kao, and K. Voss. Implementing WS-Agreement in a Globus Toolkit 4.0 Environment. in Usage of Service Level Agreements in Grids Workshop in conjunction with The 8th IEEE International Conference on Grid Computing (GRID2007), 2007, Austin, Texas.

4. Pichot, A., Wieder, P., Waldrich, O., and Ziegler, W. Dynamic SLA Negotiation based on WS-Agreement, COREGRID Technical Report, 2007