Comprehensive and Detailed Explanation From Exact Extract:
The SRE Book provides a precise definition: “SLIs are the carefully defined quantitative measures of some aspect of the level of service provided. SLOs are the target values or ranges for these indicators.” (SRE Book – Chapter: Service Level Objectives). This establishes a clear hierarchical relationship: SLIs are the measurements, while SLOs define the acceptable target levels for those measurements.
Therefore, option A is correct: SLIs measure things like latency, availability, throughput, and error rate.
SLOs then define the goal such as “99.9% availability over 30 days.”
Option B reverses the relationship.
Option C incorrectly says SLOs measure SLIs, which is backwards.
Option D confuses metrics and targets.
Thus, A is the only choice that aligns with Google’s official SRE definitions.
[References:, Site Reliability Engineering: How Google Runs Production Systems, Chapter: “Service Level Objectives.”, The Site Reliability Workbook, Chapter: “Implementing SLOs.”, ]
