An Application of Dynamic Service Level Agreements in a Risk-Aware Grid Environment Sanaa Sharaf and Karim Djemame School of Computing University of Leeds

22 Grid 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

33 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 Service Level Agreement 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 SLA Name Context Service Level Agreement

44 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)

55 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 AgreeRefuse EPR to the agreement CreateAgreement(offer) Return fault Templates GetResourceProperty

66 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.

77 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

88 Current Agreement state machine Extending WS-Agreement Rejected Observed And Terminatin g Pending and Terminating Pending Observed Terminated Complete Modified Offer Received Proposed Agreement state machine Rejected Observed and Terminatin g Pending and Terminating Pending Observed Terminated Complete Offer Received

99 AssessGrid: Risk-aware Broker and Provider(s) End user Broker Provider Reliable and trustworthy Grid provider? Reliable services for workflow mapping? Improve efficiency, reliability, and trust to attract Grid users? Grid resources What is the risk of assigning an SLA? What is the risk of accepting an SLA? AssessGrid: Advanced Risk Assessment & Management for Trustable Grids

10 AssessGrid: Architectural Overview RMS: Resource Management System

11 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

12 Customer Provider I can do X instead of Y for you for Z in return? SLA Need to ensure both parties get a better deal through the new agreement Request to re-negotiate Accept Reject 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)

13 Customer Provider Can you do X for me for Y in return? SLA Need to define specific properties in the agreement: Re-negotiation needs an EPR Request to re-negotiate SLA-Accept SLA-Reject Example: user would like to increase the price to get a lower Probaility of Failure SLA Re-Negotiation (optimistic scenario)

14 Customer Provider I can do X for you for Y in return? SLA Need to ensure both parties get a better deal through the new agreement Request to re-negotiate Accept Reject Example: provider is able to provide a better service - increase the price - lower Probability of Failure SLA Re-Negotiation (optimistic scenario)

15 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 References 1. 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) Amsterdam, Netherlands: IEEE Computer Society: p 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), 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