Demystifying SLAs, SLOs, and SLIs: A Guide to Service Reliability


In the realm of service management and reliability engineering, three acronyms often take center stage: SLAs, SLOs, and SLIs. Understanding these terms and their interplay is crucial for organizations striving to deliver reliable and high-performing services. This blog post serves as your comprehensive guide to demystifying SLAs, SLOs, and SLIs.

These terms are used in SRE planning and practice. The idea that metrics should be closely tied to business objectives.

Availability, in SRE terms, defines whether a system is able to fulfill its intended function at a point in time. In addition to being used as a reporting tool, the historical availability measurement can also describe the probability that your system will perform as expected in the future.

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SLA: Service Level Agreements

  • An SLA (service level agreement) is an agreement between provider and client about measurable metrics like uptime, responsiveness, and responsibilities. 
  • These agreements are typically drawn up by a company’s new business and legal teams and they represent the promises you’re making to customers—and the consequences if you fail to live up to those promises. Typically, consequences include financial penalties, service credits, or license extensions.

SLO: Service Level Objectives

  • An SLO (service level objective) is an agreement within an SLA about a specific metric like uptime or response time. So, if the SLA is the formal agreement between you and your customer, SLOs are the individual promises you’re making to that customer. 
  • SLOs are what set customer expectations and tell IT and DevOps teams what goals they need to hit and measure themselves against.
  • Any discussion we have in the future about whether the system is running sufficiently reliably and what design or architectural changes we should make to it must be framed in terms of our system continuing to meet this SLO.

SLI: Service Level Indicator

  • An SLI (service level indicator) measures compliance with an SLO (service level objective).
  • So, for example, if your SLA specifies that your systems will be available 99.95% of the time, your SLO is likely 99.95% uptime and your SLI is the actual measurement of your uptime. Maybe it’s 99.96%. Maybe 99.99%. 
  • To stay in compliance with your SLA, the SLI will need to meet or exceed the promises made in that document.

In addition to SLAs (Service Level Agreements), SLIs (Service Level Indicators), and SLOs (Service Level Objectives), there are several other terms and concepts commonly associated with service level management. Here are some of them:

  • SLR: Service Level Requirement
    • SLRs are the customer’s requirements and expectations for a service. These requirements are used as a basis for negotiating and establishing SLAs.
  • OLA: Operational Level Agreement
    • OLAs are agreements between different teams or departments within the same organization. They define the support and operational aspects required to meet SLAs.
  • SLP: Service Level Plan
    • An SLP is a document that outlines the details of how SLAs, SLIs, and SLOs will be achieved. It often includes information on processes, responsibilities, and resources.
  • UC: Underpinning Contract
    • Underpinning contracts are agreements between a service provider and external suppliers. These contracts support the delivery of the service and help meet SLAs.
  • KPI: Key Performance Indicator
    • KPIs are specific metrics used to measure the performance of a process, service, or organization. While SLIs are a form of KPI, KPIs can extend beyond service level management.
  • MTTR: Mean Time to Recovery
    • MTTR represents the average time it takes to restore a service after a failure or incident. It is a crucial metric in incident management.
  • MTBF: Mean Time Between Failures
    • MTBF is the average time between the occurrence of failures. It is often used to measure the reliability of a system or component.
  • RTO: Recovery Time Objective
    • RTO is the maximum acceptable time within which a service or system must be restored after an outage or disruption.
  • RPO: Recovery Point Objective
    • RPO is the maximum acceptable data loss that an organization is willing to tolerate in the event of a disaster or data loss incident.
  • CSF: Critical Success Factor
    • CSFs are the essential areas where satisfactory performance is necessary for achieving SLAs and business objectives.
  • CSI: Continuous Service Improvement
    • CSI is an ongoing process to improve the efficiency, effectiveness, and performance of a service over time.


Mastering the intricacies of SLAs, SLOs, and SLIs is fundamental to achieving service reliability. By establishing clear indicators, setting measurable objectives, and formalizing commitments through SLAs, organizations can build robust and dependable services that meet user expectations. This blog post has equipped you with the knowledge needed to navigate this vital terrain, empowering you to enhance the reliability of your services.


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Arunlal A

Senior System Developer at Zeta. Linux lover. Traveller. Let's connect! Whether you're a seasoned DevOps pro or just starting your journey, I'm always eager to engage with like-minded individuals. Follow my blog for regular updates, connect on social media, and let's embark on this DevOps adventure together! Happy coding and deploying!

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