In Site Reliability Engineering (SRE) practices, the first step during an incident is to diagnose the problem before taking corrective actions. The issue reported is that users in a specific region cannot connect to the application, indicating a regional failure.

• Option A (rerouting traffic) is a mitigation tactic but should not be done first without understanding the root cause, as it might overload other regions or mask underlying issues.
• Option B (checking CPU/memory spikes via Stackdriver Monitoring) could identify resource constraints but is too narrow; connection failures might stem from network issues, configuration errors, or application bugs not reflected in CPU/memory.
• Option C (adding high-resource node pools) is a reactive scaling measure that addresses symptoms (e.g., resource exhaustion) but not the root cause and wastes resources if misdiagnosed.
• Option D (inspecting logs via Stackdriver Logging) is the best first step. Logs provide direct error messages, stack traces, and contextual clues (e.g., network timeouts, authentication failures, or regional misconfigurations) to pinpoint the exact failure. This aligns with SRE principles of data-driven diagnosis, minimizing guesswork, and ensuring efficient resolution.