SRE: SLA vs SLO vs SLI

sla

SLA — Service Level Agreement. It’s more law-related. It’s about contracts.
SLI — Service Level Indicator. It’s some parameter that should be measured and which should be kept in some range.
SLO — Service Level Objective. It says how often SLI could fail. Like SLI should be true for 99.9% of the time.

Video from Google’s engineer (in Russian) — https://youtu.be/avdS6aIs4yI

Another look on that:

An SLI is a service level indicator; a carefully defined quantitative measure of some aspect of the level of service that is provided. e.g Request Latency, Error Rate.

An SLO is a service level objective; a target value or range of values for a service level that is measured by an SLI. e.g. 95% of /homescreen calls will complete in less than 100 ms.

SLAs are service level agreements; an explicit or implicit contract with stakeholders that includes consequences of meeting (or missing) the SLOs they contain.

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