What are Service-Level Objectives (SLOs)?
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Quick Answer
An SLO is a target for a service reliability, expressed on a Service-Level Indicator (SLI) — for example 99.9% of requests succeed under 300ms over 30 days. It sets the bar for acceptable performance.
Detailed Answer
SLIs are the measurements (availability, latency, error rate); SLOs are the targets on them; SLAs are the contractual promises (usually looser than SLOs) with consequences. The gap between 100% and the SLO is the error budget, which governs how much risk/change you can spend. SLOs turn reliability into a data-driven decision tool.
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Interview Tip
Chain SLI to SLO to SLA and mention error budgets — this is the SRE vocabulary interviewers probe.
slosrereliability