[O.SI.5] Set and monitor service level objectives against performance standards
Category: RECOMMENDED
Teams should define and document Service Level Objectives (SLOs) for every service, regardless of whether it is directly consumed by external customers or used internally. SLOs should be accessible and clearly communicate the expected standard of performance and availability for the service. While Service Level Agreements (SLAs), which define a contract that must be met for service availability, are typically defined and published for services that are directly consumed by customers, it is equally important to establish SLOs for services consumed internally. Such SLOs help ensure performance standards are met, even in the absence of formal SLAs, and can also act as data points for meeting Key Performance Indicators (KPIs).
The creation of SLOs should be a collaborative effort involving both the business and technical teams. The technical team must provide realistic estimations based on the system's capabilities and constraints, while the business team ensures these align with the company's business objectives and internal standards.
SLOs should be SMART (Specific, Measurable, Achievable, Relevant, and Time-bound). This means that they should clearly define what is to be achieved, provide a way to measure the progress, ensure that the goals can realistically be achieved given the current resources and capabilities, align with business objectives, and set a time frame for the achievement of these goals.
When defining SLOs, rather than using averages, it is preferable to use percentiles for measurement. Percentiles are more reliable in detecting outliers and provide a more accurate representation of the system's performance. For example, a 99th percentile latency SLO means that 99% of requests should be faster than a specific threshold, providing a much more accurate depiction of the service's performance than an average would.
Teams internally measure and monitor their SLOs to ensure they are meeting the defined business and technical objectives. When measuring against a SLO, teams produce Service Level Indicators (SLIs), which are the actual measurements of the performance and availability of the service at that point in time. SLIs are used to evaluate whether the service is meeting the defined SLOs. By continuously tracking SLIs against the target SLOs, teams can detect and resolve issues that impact the performance and availability of their services while ensuring that they continue to meet both external customer expectations and internal performance standards.
Continuous improvement and periodic review of SLOs are required to ensure they remain realistic and aligned with both the system's capabilities and the business's objectives. Any changes to the system that could affect its performance should trigger a review of the associated SLOs.
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