Service Level Objective (SLO)
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 a misunderstanding. There is often confusion in the use of SLA and SLO. SLOs are specific measurable characteristics of the SLA such as availability, throughput, frequency, response time, or quality. 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.
Service Level Objectives (SLOs) are often quantitative and have related measurements. Qualitative SLOs also provide extra insights for making such an informed decision. Perspectives from businesses are also important as they may highlight specific issues that only a real-life scenario can bring.
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 a "commitment to maintaining a particular state of the 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:
- Obliged - The entity that is required to deliver the SLO.
- Validity Period - The time in which the SLO will be delivered.
- Expression - This is the actual language that defines what the SLO will be.
- Optionally an EvaluationEvent may be 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.
To define service-level objectives:
- Specify the terms in which to state objectives.
- Document the current workload--the amount and categories of work. For example:
- Group the categories according to the needs of the business (for example, accounting, sales, order entry, and so on). Categorize your workload to establish priorities and different objectives. Reclassify workload based on the organization's needs.
- Measure and document resources used by each workload category during acceptable response times.
- Set service-level objectives for each workload category using these acceptable response times and activity loads.