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In this article, we learn about SLA vs SLO vs SLI: What’s the Difference and more.

SLA, SLO, and SLI represent a hierarchy of service performance commitments: an SLA (Service Level Agreement) is a formal, customer-facing contract with consequences for non-compliance; an SLO (Service Level Objective) is an internal target for system reliability that aims to meet the SLA; and an SLI (Service Level Indicator) is the specific, measurable metric that tracks performance and determines if the SLOs are being met. 

Here’s a breakdown of each term:

SLA: Service Level Agreement

• What it is:A formal, legally binding contract or agreement between a service provider and a customer. 
• Purpose:To define the expected level of service, including uptime or performance, and outline the penalties or consequences for failing to meet these levels. 
• Example:A cloud service provider might offer service credits to a customer if their virtual machine uptime drops below a certain percentage in a given month. 

SLO: Service Level Objective

• What it is: An internal, specific, and measurable performance target for a service. 
• Purpose: To set a clear goal for IT and DevOps teams to ensure that the service consistently performs at a level that satisfies customer expectations and meets the commitments defined in the SLA. 
• Example: A target of “99.95% uptime for virtual machines per month” could be an SLO for a cloud service provider. 

SLI: Service Level Indicator 

• What it is:A direct, quantitative measurement of a service’s behavior or a specific performance metric. 
• Purpose:To track the actual performance of the service and provide the data needed to determine if the SLOs are being met. 
• Example:For the SLO of 99.95% uptime, the SLI would be the actual measured uptime percentage of the virtual machines. 

The Hierarchy

• SLIs: are the raw, measured data points. 
• SLOs: are the targets set for these SLIs to ensure reliability and meet performance goals. 
• SLAs: are the formal promises made to customers, with the understanding that the internal SLOs and the SLI data will be used to uphold those promises.