Service level language is a way an organization can set targets for different aspects of product quality, especially areas like availability and performance. Both of us have worked in organizations that have used SLAs (Service-level agreements), but we’ve learned more detail from Abby Bangser who says “Operations engineers improved how they measure quality as complexity and expectations have grown.”

Three high-level definitions that are important to know are:

• Service-level indicator (SLI): ways to measure success and make informed decisions
• Service-level objective (SLO): targets and priorities for quality and performance
• Service level agreement (SLA): customer agreement, along with associated penalties

Service-Level Indicator (SLI)

An SLI is a measure of an aspect of the level of service provided. It is a service level indicator—a carefully defined quantitative measure of some aspect of the level of service that is provided.

  * Feedback from production and test environments

  * Monitor thresholds for each service’s availability; investigate anomalies

  * Typical metrics include availability, latency, throughput, error rate, durability (long-term data retention). Examples:

           - successful requests as a % of all requests  

           -  ratio of home page requests that loaded in < 100 ms.

  * Testers can ask questions and get examples to identify meaningful SLIs

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