SLO: a measurable goal for a service, e.g. "99.9% of requests under 300ms over 30 days". It guides engineering priorities and is stricter than the external SLA promised to customers.
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How does an SLI (Service Level Indicator) relate to an SLO?
SLI vs SLO: the SLI is the quantitative measurement (e.g., current success rate of 99.95%). The SLO is the threshold you commit the SLI to satisfy. You track the SLI against the SLO target.
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What is an error budget?
Error budget: the complement of the SLO. A 99.9% target permits 0.1% failures. Teams spend this budget on risk (shipping features); if it runs out, they freeze releases to focus on reliability.
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What does the term burn rate describe for an error budget?
Burn rate: a multiplier of normal consumption. A burn rate of 10x means you are spending the budget ten times faster than sustainable, which should trigger an urgent alert before the budget is exhausted.
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Why is an SLO usually stricter than the published SLA?
SLO buffer: teams set internal SLOs tighter than the contractual SLA so that breaching the SLO is an early warning, giving them time to fix issues before the SLA (and its penalties) is violated.