This PCDOE practice question tests your understanding of implementing service monitoring strategies. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
An SRE team needs to define an SLI for a web service's availability SLO of 99.9%. Which metric should they use?
Error budget
Why wrong: Error budget is derived from SLO, not an SLI metric.
CPU utilization
Why wrong: CPU utilization is a system metric, not service availability.
Request latency (p99)
Why wrong: Latency measures speed, not availability.
Uptime check success rate
Uptime checks measure the fraction of successful probes, directly reflecting availability.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Uptime check success rate
Option D is correct because an uptime check success rate directly measures the proportion of time the service is reachable and responding, which aligns with the definition of availability for a 99.9% SLO. This metric is typically derived from synthetic probes or health check endpoints (e.g., HTTP 200 responses) and reflects the binary state of the service being up or down, making it the appropriate SLI for availability.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
Error budget
Why it's wrong here
Error budget is derived from SLO, not an SLI metric.
CPU utilization
Why it's wrong here
CPU utilization is a system metric, not service availability.
Request latency (p99)
Why it's wrong here
Latency measures speed, not availability.
Uptime check success rate
Why this is correct
Uptime checks measure the fraction of successful probes, directly reflecting availability.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Google Cloud often tests the distinction between availability (binary up/down) and performance (latency/error rate), so candidates mistakenly choose latency metrics like p99 for availability SLOs, conflating responsiveness with uptime.
Detailed technical explanation
Uptime checks typically use HTTP GET requests to a health endpoint (e.g., /healthz) and evaluate the response status code (e.g., 2xx) and optionally the response body. In distributed systems, availability SLIs must account for both the control plane (e.g., load balancer health checks) and data plane (e.g., actual user requests), as a service might pass a simple ping but fail to serve real traffic due to backend dependencies. Real-world scenarios often require multi-region synthetic checks to avoid false positives from local network issues.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
An e-commerce site experiences heavy traffic on Black Friday and near-zero traffic during off-peak weeks. Rather than provisioning permanent large VMs, the team uses auto-scaling groups that add capacity automatically under load and reduce it overnight. Questions like this test whether you understand elasticity, availability zones, and cloud compute scaling patterns.
What to study next
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FAQ
Implementing service monitoring strategies — This question tests Implementing service monitoring strategies — Read the scenario before looking for a memorised answer..
The correct answer is: Uptime check success rate — Option D is correct because an uptime check success rate directly measures the proportion of time the service is reachable and responding, which aligns with the definition of availability for a 99.9% SLO. This metric is typically derived from synthetic probes or health check endpoints (e.g., HTTP 200 responses) and reflects the binary state of the service being up or down, making it the appropriate SLI for availability.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 30, 2026
This PCDOE practice question is part of Courseiva's free Google Cloud certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the PCDOE exam.
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