176:, 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)
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service in a given period" with respect to the state of the SLA parameters. 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.
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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.
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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
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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 are 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
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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". Keller and Ludwig more concisely define an SLO as "commitment to maintain a particular state of the
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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,
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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.
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The SLO term is found in various scientific papers, for instance in the reference architecture of the SLA@SOI project, and it is used in the Open Grid Forum document on WS-Agreement.
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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.
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What are SLOs? How service-level objectives work with SLIs to deliver on SLAs
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Expression - This is the actual language that defines what the SLO will be.
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98% of severity 3 tickets will be resolved within three business days
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98% of severity 4 tickets will be resolved within five business days
340:"Site Reliability Engineering: How Google Runs Production Systems"
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The SLO are formed by setting goals for metrics (commonly called
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98% of severity 2 tickets will be resolved within eight hours
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99% of severity 1 tickets will be resolved within three hours
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100% of help desk calls will be answered within three minutes
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75% of help desk calls will be answered in less than a minute
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Validity Period - The time in which the SLO will be delivered.
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99.5% of TCP replies within 4 seconds of receiving a request
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85% of TCP replies within 1.5 seconds of receiving a request
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85% of help desk calls will be answered within two minutes
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Obliged - The entity that is required to deliver the SLO.
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The application will be available 99.95% of the time
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394:: 465074.
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317:Term usage
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