Service-level objective: Difference between revisions

Revision as of 22:21, 22 February 2017

Revision as of 18:33, 23 February 2017

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==Overview==

There is often confusion in the use of SLAs and SLOs. The SLA is the entire agreement that specifies what service is to be provided, how it is supported, times, locations, costs, performance, and responsibilities of the parties involved. SLOs are specific measurable characteristics of the SLA such as availability, throughput, frequency, response time, or quality. These SLOs together are meant to define the expected service between the provider and the customer and vary depending on the service's urgency, resources, and budget. SLOs provide a quantitative means to define the level of service a customer can expect from a provider.<ref name=":1">{{Cite journal|last=Rastegari|first=Yousef|last2=Shams|first2=Fereidoon|date=2015-12-29|title=Optimal Decomposition of Service Level Objectives into Policy Assertions|url=http://www.hindawi.com/journals/tswj/2015/465074/|journal=The Scientific World Journal|language=en|volume=2015|pages=1–9|doi=10.1155/2015/465074|issn=2356-6140|pmc=4709918|pmid=26962544}}</ref>.

The SLO may be composed of one or more [[quality of service]] (QoS) measurements ([[service level indicator]]s, SLIs) that are combined to produce the SLO achievement value. As an example, an availability SLO may depend on multiple components, each of which may have a QoS availability measurement. The combination of QoS measures into an SLO achievement value will depend on the nature and architecture of the service.

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* Mutually acceptable

While Andrieux et. al. define the SLO as "the quality of service aspect of the agreement. Syntactically, it is an assertion over the terms of the agreement as well as such qualities as date and time" .<ref name=":0" />. Keller and Ludwig more concisely define an SLO as "commitment to maintain a particular state of the service in a given period" with respect to the state of the SLA parameters .<ref>Alexander Keller, Heiko Ludwig "The WSLA Framework: Specifying and Monitoring Service Level Agreements for Web Services", Journal of Network and Systems Management, Vol 11, n. 1, March 2003.</ref>. Keller and Ludwig go on to state that while service providers will most often be the lead entity in taking on SLOs there is no firm definition as such and any entity can be responsible for an SLO. Along with this an SLO can be broken down into a number of different components.

* Obliged - The entity that is required to deliver the SLO.

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Optionally an EvaluationEvent maybe assigned to the SLO, an EvaluationEvent is defined as the measure by which the SLO will be checked to see if it's meeting the Expression.

SLOs should generally be specified in terms of an achievement value or service level, a target measurement, a measurement period, and where and how they are measured.<ref name=":1" />. As an example, "90% of calls to the helpdesk should be answered in less than 20 seconds measured over a one-month period as reported by the [[Automatic call distributor|ACD system]]". Results can be reported as a percent of time that the target answer time was achieved and then compared to the desired service level (90%).

{| class="wikitable"

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|Service Desk Response

|75% of help desk calls will be answered in less than a minute

85% of help desk calls will be answered within two minutes

100% of help desk calls will be answered within three minutes