OGF19 -- NC 1 Service Level Agreements and QoS: what do we measure and why? Omer F. Rana School of Computer Science, Cardiff University, UK Welsh eScience Centre, UK

2 OGF19 – NC (QoS BoF) QoS Management QoS has been explored in: Computer Networks Bandwidth, Delay, Packet loss rate and Jitter. Multimedia Applications Frame rate and computation resource. Grid Computing Network QoS, computation and storage requirements.

3 OGF19 – NC (QoS BoF) Continue … QoS management: Covers a range of different activities, from resource specification, selection and allocation through to resource release. QoS system should address the following: Specifying QoS requirements Mapping of QoS requirements to resource capability Negotiating QoS with resource owners Establishing contracts / SLAs with clients Reserving and allocating resources Monitoring parameters associated with QoS sessions Adapting to varying resource quality characteristics Terminating QoS sessions User Expectations vs. Resource Management

4 OGF19 – NC (QoS BoF) When QoS is needed? Interactive sessions Computation steering (control parameters & data exchange) Interactive visualization (visualization & simulations services) Response within a limited time span Co-scheduling or co-location support From SCIRun, University of Utah – Application QoS – User perception, response time, appl. Security, etc. – Middleware QoS – Comp., Memory and Storage – Network QoS – BW, Packet loss, Delay, Jitter

5 OGF19 – NC (QoS BoF) What is a Service Level Agreement (SLA)? Client Provider Can you do X for me for Y in return? Yes SLA Distinguish between: Discovery of suitable provider Establishment of an SLA P2P Search, Directory Service SLA-Offer SLA-Accept SLA-Reject A relationship between a client and provider in the context of a particular capability (service) provision

6 OGF19 – NC (QoS BoF) What is an SLA? Client Provider Can you do X for me for Y in return? No, but I can do Z for Y SLA Accept SLA-CounterOffer SLA-Offer SLA-Accept SLA-Reject

7 OGF19 – NC (QoS BoF) What is an SLA? Client Provider Can you do X for me for Y in return? No SLA Can you do Z for me for Y in return? Negotiation Phase (Single or Multi-Round) SLA-Offer SLA-CounterOffer SLA-OfferDependency

8 OGF19 – NC (QoS BoF) Variations Client Providers SLA Client Providers SLA Multi-provider SLA Single SLA is divided across multiple providers (e.g. workflow composition) SLA dependencies For an SLA to be valid, another SLA has to be agreed (e.g. co-allocation)

9 OGF19 – NC (QoS BoF) QoS Context QoS: Per Service Per Workflow (Set of Services) Workflow: Aggregating metrics across services Support through some workflow enactor

10 OGF19 – NC (QoS BoF) Dynamically established and managed relationship between two parties Objective is delivery of a service by one of the parties in the context of the agreement Delivery involves: Functional QoS Properties What is an SLA? SLA

11 OGF19 – NC (QoS BoF) Forming the Agreement Distinguish between: Agreement itself Mechanisms that lead to the formation of the agreement Mechanisms that lead to agreement: Negotiation (single or multi-shot) One-shot creation Policy-based creation of agreements, etc.

12 OGF19 – NC (QoS BoF) WS-Agreement Name/ID Context Terms Composition Guarantee Terms Service Terms Agreement Information about Agreement Initiator Responder Expiration Time Information about Service Service Description Terms (generally, these are domain dependent) Information about Service Level Service Level Objectives, Qualifying Conditions for the agreement to be valid, Penalty Terms, etc

13 OGF19 – NC (QoS BoF) WS-Agreement Terms From: Viktor Yarmolenko (U Manchester)

14 OGF19 – NC (QoS BoF) SLA Life Cycle Identify Provider On completion of a discovery phase Define SLA Define what is being requested Agree on SLA terms Agree on Service Level Objectives Monitor SLA Violation Confirm whether SLOs are being violated Destroy SLA Expire SLA Penalty for SLA Violation

15 OGF19 – NC (QoS BoF) CATNETs: Metrics Pyramid

16 OGF19 – NC (QoS BoF) SLA Classes Guaranteed constraints to be exactly observed SLA is precisely/exactly defined adaptation algorithm/optimization heuristics Controlled-load some constraints may be observed Range-oriented SLA optimization heuristics Best-effort any resources will do no adaptation support

17 OGF19 – NC (QoS BoF) Adaptation Algorithm Assume a total capacity: C= C G + C A + C B where G, A & B denotes guaranteed, adaptive and best effort Adapt(c(u,t), g(u)) Net capacity N G (t) = C G (t) – If N G (t) < 0; (guarantees cant be honoured) Then ADD ( - C G (t)) from A to G ADD (C A (t) – [ - C G (t)]) from A to B Before invoking the adaptive function: Ensuring that the request at time (t) g(u) --- (SLA) Ensuring that C G CG(t): Capacity in guaranteed block at time t; g(u): guarantee to user user u

18 OGF19 – NC (QoS BoF) SLA Adaptation Assume capacity Total : C= C G + C A + C B best effort can uses the adaptive capacity, as long as its not used by the guaranteed When QoS degrades for guaranteed Then adaptive is utilized to compensate for the degradation best effort can still utilize the remaining capacity of the adaptive, as long as its not used by the guaranteed When the congested capacity is restored, the adaptive capacity can be used entirely by the best effort GAB GBA GAB BAG GBA o Before invoking the adaptive function: o Ensuring that the request at time (t) the agreed upon in the SLA o Ensuring that the total capacities within all SLAs at time (t) C G Aim: compensation for QoS degradation for guaranteed class only

19 OGF19 – NC (QoS BoF) SLA Adaptation If we define a set: QoS = { a 1, a 2,..., a n }, where each a i represents a different parameter of interest such as CPU, network bandwidth, etc. Then we could compare sets: QoS x = { a 1x,..., a nx } and QoS y = {a 1y,..., a ny } QoS values specified in SLA as: a y a i a x Or a i ={ x, y, z } Assume the existence of a cost function: Cost(a i ) = c i * a i Then: Service_ Cost (QoS) = The proposed heuristic: Total Cost = max n is the total number of active services The QoS broker implements this heuristic by varying the resource quality selection, based on the agreed upon in the SLA, aiming to Optimize resource utilization and maximize the overall cost. This heuristic could be mapped to the Generalized Assignment Problem (GAP)

20 OGF19 – NC (QoS BoF) Grid Node Reservation ManagerAllocation Manager Policy Manager QoS Grid Service Resources Grid QoS service interface

21 OGF19 – NC (QoS BoF) Main components Policy Manager To provide dynamic info about the domain-specific resource characteristics and policy Reservation Manger To provide advance/immediate resource reservation Data structure contains reservation entries Interact with policy manager for resource char. Allocation Manger To interact with the underlying resource manager for resource allocation (e.g DSRT, Bandwidth Broker)

22 OGF19 – NC (QoS BoF) UDDIe QoS Broker Grid node 1 Grid node 2Grid node 3 QoS Discovery Client's Appl. QoS service ReservationAllocation Policy QoS service ReservationAllocation Policy QoS service ReservationAllocation Policy SLA Joint work with Argonne National Lab. (Gregor von Lazweski et al.)

23 OGF19 – NC (QoS BoF) Reservation Approaches Resource reservation / allocation based on two strategies: Time-domain: reserve the whole compute power of Grid node. Guaranteed exclusive access Resource-domain: reserve a CPU slot of the Grid node. Shared access – guaranteed resource capacity Suitable for light weight applications/services.

24 OGF19 – NC (QoS BoF) Best Effort

25 OGF19 – NC (QoS BoF) Guaranteed

26 OGF19 – NC (QoS BoF)