Which of these is NOT a supported monitoring event type in CloudMonitor?

The identification of the event type that is not supported by CloudMonitor revolves around understanding the capabilities that the service offers for the monitoring of various Alibaba Cloud resources.

CloudMonitor provides monitoring for multiple services, including Elastic Compute Service (ECS), Object Storage Service (OSS), and Server Load Balancer (SLB). Therefore, the options related to application crashes for ECS, bucket bandwidth monitoring for OSS, and certificate expiration events for SLB are all valid monitoring events.

Specifically, the query focuses on database connection failures for Relational Database Service (RDS). While CloudMonitor does allow for monitoring various metrics and events associated with RDS instances, direct monitoring of connection failures as a distinct event type is not typically listed among its supported events. Instead, the typical monitoring features may include tracking CPU usage, memory consumption, storage, and other performance-related metrics but not failures in connections. This distinction is critical as it showcases the designed focus of CloudMonitor in providing performance insights rather than directly capturing all types of application-layer errors such as database connection issues.

Overall, the answer correctly identifies an event type that does not align with the capabilities of CloudMonitor, demonstrating the service's emphasis on performance metrics rather than detailed application-level event failures.