Service-level objective: Difference between revisions

Revision as of 23:34, 10 February 2017

Revision as of 01:44, 12 February 2017

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==Overview==

There is often confusion in the use of SLA and SLO. 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>{{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=PMC4709918|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

In <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> the authors define a SLO as a "commitment to maintain a particular state of the service in a given period" with respect to the state of the SLA parameters. They also 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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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're measured. 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, then compared to the desired service level (90%).

{| class="wikitable"

!Type of Measure

!Example SLO Requirement

!Measurement Period

|-

|Availability

|The application will be available 99.95% of the time

|Over a year

|-

|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

|Over a month

|-

|Incident Response Time

|99% of severity 1 tickets will be resolved within three hours

98% of severity 2 tickets will be resolved within eight hours

98% of severity 3 tickets will be resolved within three business days

98% of severity 4 tickets will be resolved within five business days

|Over a quarter

|-

|Response Time

|85% of TCP replies within 1.5 seconds of receiving a request

99.5% of TCP replies within 4 seconds of receiving a request

|Over a month

|}

==Term Usage==