Microsoft Certified: DevOps Engineer ExpertImplement a Site Reliability Engineering (SRE) strategyEasy
A DevOps team is adopting an SRE strategy for a critical e-commerce platform hosted on Azure. They want to define a Service Level Objective (SLO) for the platform's average response time. The business requires that 95% of all user requests complete within 500 milliseconds. Which of the following SLI definitions most accurately supports this SLO?
- AThe 95th percentile of response times must be less than 500 milliseconds.
- BThe 99th percentile of response times must be less than 500 milliseconds.
- CThe maximum response time must be less than 500 milliseconds for all requests.
- DAverage response time must be less than 500 milliseconds for all requests.
Show answer & explanationAnswer & explanation
Correct answer: A. The 95th percentile of response times must be less than 500 milliseconds.
The business requirement specifies that '95% of all user requests complete within 500 milliseconds'. This directly translates to using the 95th percentile as the Service Level Indicator (SLI) to measure against the Service Level Objective (SLO).
Why the other options are wrong
- B. The 99th percentile is a stricter measure, meaning 99% of requests must be below the threshold, which goes beyond the stated 95% requirement.
- C. The maximum response time is too strict; even a single slow request could violate this, which is not what the 95% requirement implies.
- D. Using the average response time does not account for the tail latency that affects a certain percentage of users, which is critical for the given SLO.
Percentile-based SLI
A Service Level Indicator (SLI) that measures the percentage of requests or operations that complete within a specific time threshold, often used to capture user experience variations.
- Captures tail latency issues.
- Commonly expressed as 'X% of requests complete within Y milliseconds'.
- Directly aligns with user experience expectations.
Memory trick: Percentiles paint the truest picture of user experience.