This AZ-400 practice question tests your understanding of implement an instrumentation strategy. 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.
Which TWO metrics should you monitor to evaluate the reliability of a web application according to the DORA metrics?
Lead Time for Changes
Why wrong: This measures speed, not reliability.
Change Failure Rate
Measures how often deployments cause failures.
Mean Time to Restore (MTTR)
Measures how quickly you recover from failures.
CPU Usage
Why wrong: Not a DORA metric.
Deployment Frequency
Why wrong: This measures velocity, not reliability.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Change Failure Rate
The DORA metrics define four key measures for software delivery performance: Deployment Frequency, Lead Time for Changes, Mean Time to Restore (MTTR), and Change Failure Rate. For evaluating the reliability of a web application, the two most directly relevant metrics are Change Failure Rate (B), which measures the percentage of deployments causing a failure in production, and Mean Time to Restore (MTTR) (C), which measures the time it takes to recover from a failure. These two metrics directly quantify stability and resilience, whereas Deployment Frequency and Lead Time for Changes focus on throughput and speed.
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.
Lead Time for Changes
Why it's wrong here
This measures speed, not reliability.
Change Failure Rate
Why this is correct
Measures how often deployments cause failures.
Related concept
Read the scenario before looking for a memorised answer.
Mean Time to Restore (MTTR)
Why this is correct
Measures how quickly you recover from failures.
Related concept
Read the scenario before looking for a memorised answer.
CPU Usage
Why it's wrong here
Not a DORA metric.
Deployment Frequency
Why it's wrong here
This measures velocity, not reliability.
Common exam traps
The trap here is that candidates often confuse throughput metrics (Deployment Frequency, Lead Time for Changes) with reliability metrics, but DORA specifically separates them into 'throughput' and 'stability' categories, and the question explicitly asks for reliability.
Detailed technical explanation
Change Failure Rate is calculated as the number of failed deployments divided by the total number of deployments, often tracked via incident management tools like PagerDuty or Azure Monitor. MTTR is the average time from when a failure is detected (e.g., via a synthetic transaction alert) to when the service is fully restored, including rollback, hotfix, or failover. In practice, a low Change Failure Rate (e.g., <15%) and a low MTTR (e.g., <1 hour) are hallmarks of a mature DevOps practice, as defined by the 2023 Accelerate State of DevOps Report.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A cloud solutions architect for a retail company is evaluating services for a new workload. The correct answer here reflects best practice for the specific scenario described — not a general cloud recommendation. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Cloud exam questions reward reading the constraint carefully: the same technology can be right or wrong depending on the use case.
What to study next
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FAQ
Implement an instrumentation strategy — This question tests Implement an instrumentation strategy — Read the scenario before looking for a memorised answer..
The correct answer is: Change Failure Rate — The DORA metrics define four key measures for software delivery performance: Deployment Frequency, Lead Time for Changes, Mean Time to Restore (MTTR), and Change Failure Rate. For evaluating the reliability of a web application, the two most directly relevant metrics are Change Failure Rate (B), which measures the percentage of deployments causing a failure in production, and Mean Time to Restore (MTTR) (C), which measures the time it takes to recover from a failure. These two metrics directly quantify stability and resilience, whereas Deployment Frequency and Lead Time for Changes focus on throughput and speed.
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 11, 2026
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