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A DevOps team is developing a new microservice and needs to define its Service Level Objectives (SLOs). The microservice will handle critical customer authentication requests. Which of the following metrics is MOST appropriate to use as a Service Level Indicator (SLI) for the availability of this authentication microservice?
- ANetwork latency between the microservice and the front-end application.
- BDisk I/O operations per second for the database.
- CAverage CPU utilization of the microservice instances.
- DPercentage of successful authentication requests.
Show answer & explanationAnswer & explanation
Correct answer: D. Percentage of successful authentication requests.
For an authentication microservice, 'availability' from a user's perspective means successfully authenticating. The percentage of successful authentication requests directly measures the user-facing availability of the core function. Other options are internal resource metrics or latency, not direct indicators of successful service delivery.
Why the other options are wrong
- A. Network latency affects performance, which could be another SLI (latency), but not the primary SLI for 'availability' in terms of successful operations.
- B. Disk I/O is a backend infrastructure metric, not a direct indicator of whether the authentication microservice is available to users.
- C. CPU utilization is an internal resource metric, not a direct measure of service availability from a user's perspective.
Service Level Indicator (SLI)
A carefully defined, quantifiable measure of some aspect of the level of service that is provided.
- Directly measures user experience or service health.
- Must be measurable and actionable.
- Examples: request latency, error rate, throughput, availability.
Memory trick: SLI: 'User's view, success, direct link.'