Service-level objective: Difference between revisions

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{{short description|Key element of a service-level agreement}}

{{Refimprove|date=December 2013}}

A '''service-level objective''' (SLO) is a key element of a [[service-level agreement]] (SLA) between a [[service provider]] and a [[customer]]. SLOs are agreed upon as a means of measuring the performance of the Service Provider and are outlined as a way of avoiding disputes between the two parties based on misunderstanding.

A '''service-level objective''' ('''SLO'''), as per the O'Reilly Site Reliability Engineering book, is a "target value or range of values for a [[service level]] that is measured by an [[Service Level Indicator|SLI]]."<ref>{{cite web |first1=Chris |last1=Jones |first2=John |last2=Wilkes |first3=Niall |last3=Murphy |editor=Betsy Beyer |title=Site Reliability Engineering: How Google Runs Production Systems |url=https://sre.google/sre-book/service-level-objectives/ |website=Google Site Reliability Engineering |publisher=O'Reilly |access-date=9 June 2023}}</ref> An SLO is a key element of a [[Service-level agreement|service-level agreement (SLA)]] between a [[service provider]] and a [[customer]]. SLOs are agreed upon as a means of measuring the performance of the service provider and are outlined as a way of avoiding disputes between the two parties based on misunderstanding.

==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|lastlast1=Rastegari|firstfirst1=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|issue=1 |pages=1–9465074|doi=10.1155/2015/465074|issn=2356-6140|pmc=4709918|pmid=26962544|doi-access=free}}</ref>

The SLO mayare beformed composedby ofsetting onegoals orfor more [[quality of service]]metrics (QoS)commonly measurementscalled ([[service level indicator]]s, SLIs) that are combined to produce the SLO achievement value. As an example, an availability SLO may dependbe ondefined multipleas components,the eachexpected ofmeasured whichvalue mayof have a QoSan availability measurement.SLI Theover combinationa ofprescribed QoSduration measures(e.g. intofour anweeks). SLOThe achievementavailability valueSLI used will dependvary based on the nature and architecture of the service. For example, a simple web service might use the ratio of successful responses served vs the total number of valid requests received. (total_success / total_valid) <ref name="Hidalgo20">{{cite book |last1=Hidalgo |first1=Alex |title=Implementing Service Level Objectives |date=August 2020 |publisher=O'Reilly Media, Inc. |isbn=9781492076766 |edition=1}}</ref>

==Examples==

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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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==Term Usageusage==

The SLO term is found in various scientific papers, for instance in the reference architecture of the SLA@SOI project,<ref>Jens Happe, Wolfgang Theilmann, Andrew Edmonds, and Keven T. Kearney "A Reference Architecture for Multi-Level SLA Management" in "Service Level Agreements for Cloud Computing", eds. Wieder, Philipp and Butler, Joe M. and Theilmann, Wolfgang and Yahyapour, Ramin, Springer New York, 2011, DOI:10.1007/978-1-4614-1614-2_2</ref> and it is used in the Open Grid Forum document on WS-Agreement.<ref name=":0">Alain Andrieux, Karl Czajkowski, Asit Dan, [[Kate Keahey]], Heiko Ludwig, Toshiyuki Nakata, Jim Pruyne, John Rofrano, Steve Tuecke, Ming Xu "Web Services Agreement Specification (WS-Agreement)", GFD-R-P.107, March 2007, Open Grid Forum.</ref>

==References==

{{reflist}}

==External links==

* [https://sre.google/sre-book/service-level-objectives/ Service Level Objectives]

* [https://www.dynatrace.com/news/blog/what-are-slos/ What are SLOs? How service-level objectives work with SLIs to deliver on SLAs]

* [https://www.atlassian.com/incident-management/kpis/sla-vs-slo-vs-sli SLA vs. SLO vs. SLI: What’s the difference?]

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