PROFESSIONAL-CLOUD-DEVOPS-ENGINEER Question #36: Real Exam Question with Answer & Explanation

Question

You are responsible for the reliability of a high-volume enterprise application. A large number of users report that an important subset of the application's functionality "a data intensive reporting feature" is consistently failing with an HTTP 500 error. When you investigate your application's dashboards, you notice a strong correlation between the failures and a metric that represents the size of an internal queue used for generating reports. You trace the failures to a reporting backend that is experiencing high I/O wait times. You quickly fix the issue by resizing the backend's persistent disk (PD). How you need to create an availability Service Level Indicator (SLI) for the report generation feature. How would you define it?

Options

• AAs the I/O wait times aggregated across all report generation backends
• BAs the proportion of report generation requests that result in a successful response
• CAs the application's report generation queue size compared to a known-good threshold
• DAs the reporting backend PD throughout capacity compared to a known-good threshold

Explanation

An availability Service Level Indicator (SLI) for the report generation feature should be defined as the proportion of successful requests for that feature.

Common mistakes.

• A. I/O wait times are an internal system metric that can contribute to availability issues, but it is not a direct measure of availability from the user's perspective, making it a good diagnostic metric but not an SLI.
• C. The report generation queue size is an internal health metric that can indicate performance or backlog issues, but it does not directly represent the success or failure rate of user requests for the feature.
• D. PD throughput capacity is an infrastructure metric and a potential cause of performance issues, but it is not a direct user-centric measure of the availability of the reporting feature itself.

Concept tested. Defining Availability Service Level Indicator (SLI)

Reference. https://sre.google/sre-book/monitoring-alerting/#what-to-measure-in-an-sli

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