The Default Flow map shows a tier with a full or partial red circle, which...

According to the Troubleshoot Health Rule Violations document1, one of the ways to troubleshoot health rule violations is to click on the Events tab for the application on the Default Flow Map and then analyze the health rule(s) being violated. This will show you the details of the health rule violation events, such as the affected entity, the severity, the duration, the evaluation time, and the triggered actions. You can also drill down into the health rule violation details to see the health rule configuration, the metric values, and the snapshots. This will help you identify the root cause of the issue and take appropriate remediation actions. Therefore, the correct answer is D. Using the metric browser, disabling the health rule, or rebooting the server may not be the best or the most efficient ways to troubleshoot health rule violations, as they may not reveal the source of the problem, may affect other entities, or may not resolve the issue permanently. References:

Troubleshoot Health Rule Violations