Service-level objective: Difference between revisions

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

{{More citations needed|date=December 2013}}

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 |last1first1=Beyer,Chris |last1=Jones, Petoff,|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|last1=Rastegari|first1=Yousef|last2=Shams|first2=Fereidoon|date=2015-12-29|title=Optimal Decomposition of Service Level Objectives into Policy Assertions|journal=The Scientific World Journal|language=en|volume=2015|issue=1 |pages=465074|doi=10.1155/2015/465074|issn=2356-6140|pmc=4709918|pmid=26962544|doi-access=free}}</ref>

The SLO are formed by setting goals for metrics (commonly called [[service level indicator]]s, SLIs). As an example, an availability SLO may be defined as the expected measured value of an availability SLI over a prescribed duration (e.g. four weeks). The availability SLI used will vary 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>