OGF19 -- NC 1 Service Level Agreements and QoS: what do we measure and why? Omer F. Rana [email protected] School of Computer Science, Cardiff.

OGF19 -- NC 1

Service Level Agreements and QoS: what do we measure and why?

Omer F. Rana

[email protected] of Computer Science, Cardiff University, UKWelsh eScience Centre, UK

2OGF19 – 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.

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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

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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

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What is a Service Level Agreement (SLA)?

Client Provider

Can youdo X for mefor Y in return?

Yes

SLASLA

Distinguish between: Discovery of suitable provider Establishment of an SLA

P2P Search,Directory Service

SLA-Offer

SLA-AcceptSLA-Reject

A relationship between a client and provider in the context of a particularcapability (service) provision

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What is an SLA?

Client Provider

Can youdo X for mefor Y in return?

No, but Ican do Zfor Y

SLASLA

Accept

SLA-CounterOffer

SLA-Offer

SLA-AcceptSLA-Reject

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What is an SLA?

Client Provider

Can youdo X for mefor Y in return?

No

SLASLA

Can youdo Z for mefor Y in return?

NegotiationPhase(Single orMulti-Round)

SLA-Offer

SLA-CounterOffer

SLA-OfferDependency

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Variations

Client

Providers

SLA

Client

Providers

SLA SLA

Multi-provider SLA

Single SLA is dividedacross multiple providers(e.g. workflow composition)

SLA dependencies

For an SLA to be valid, anotherSLA has to be agreed(e.g. co-allocation)

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QoS Context QoS:

Per ServicePer Workflow (Set of Services)

Workflow:Aggregating metrics across servicesSupport through some workflow enactor

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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?

www.utilityserve.com SLA

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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 creationPolicy-based creation of agreements, etc.

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WS-Agreement

Name/ID

Context

Terms Composition

Guarantee Terms

Service Terms

AgreementInformation about AgreementInitiatorResponderExpiration Time

Information about ServiceService Description Terms(generally, these are domaindependent)

Information about ServiceLevelService Level Objectives,Qualifying Conditions for the agreement to be valid,Penalty Terms, etc

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WS-Agreement Terms

From: Viktor Yarmolenko (U Manchester)

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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 SLO’s are being violated Destroy SLA

Expire SLA Penalty for SLA Violation

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CATNETs: Metrics “Pyramid”

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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

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Adaptation Algorithm

Assume a total capacity: C= CG + CA + CB where G, A & B denotes ‘guaranteed,’ ‘adaptive’ and ‘best effort’

Adapt(c(u,t), g(u))Net capacity NG(t) = CG(t) –

If NG(t) < 0; (guarantees can’t be honoured)

Then ADD ( - CG(t)) from A to G

ADD (CA(t) – [ - CG(t)]) from A to B

Before invoking the adaptive function: Ensuring that the request at time (t) g(u) --- (SLA) Ensuring that CG

Gu

ug )(

Gu

ug )(

Gu

ug )(

Gu

ug )(

CG(t): Capacityin guaranteed blockat time t;

g(u): guarantee to useruser “u”

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SLA Adaptation

Assume capacityTotal: C= CG + CA + CB ‘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’

G A B

G BA

G A B

BAG

G BA

o Before invoking the adaptive function:o Ensuring that the request at time (t) the agreed upon in the SLAo Ensuring that the total capacities within all SLAs at time (t) CG

Aim: compensation for QoS degradation for

‘guaranteed’ class only

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SLA Adaptation

If we define a set: QoS = { a1, a2, ..., an }, where each ai represents a different parameter of interest such as CPU, network bandwidth, etc.

Then we could compare sets: QoSx = { a1x, ..., anx } and QoSy = {a1y, ..., any }

QoS values specified in SLA as: ay ai ax Or ai={ x, y, z } Assume the existence of a cost function: Cost(ai) = ci* ai

Then: Service_ Cost (QoS) =

The proposed heuristic: Total Cost = maxn is the total number of active services

n

iaici

1)*(

n

iQoSiCostService

1))(_(

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)

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Grid Node

Reservation ManagerAllocation Manager

Policy Manager

QoS Grid Service

Resources

Grid QoS service interface

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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)

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UDDIe

QoS Broker

Grid node 1 Grid node 2 Grid node 3

QoS Discovery

Client's Appl.

QoS service

ReservationAllocation

Policy

QoS service

ReservationAllocation

Policy

QoS service

ReservationAllocation

Policy

SLASLA

SLA

Joint work withArgonne National Lab.(Gregor von Lazweski et al.)

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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.

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Best Effort

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Guaranteed

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