Troubleshooting Silent Metric Loss in GMP Managed Collection

The core issue is a silent failure in metric ingestion using Google Cloud Managed Service for Prometheus (GMP) with managed collection. In this architecture, GMP discovers targets via Kubernetes custom resources, specifically PodMonitoring or ClusterPodMonitoring objects. These resources define how to scrape metrics from pods.

Option B is the correct troubleshooting step because if the PodMonitoring resource specifies an incorrect or non-existent port, the scraping job will fail silently—no data will be collected, and no immediate error message may appear in standard logs unless debug logging is enabled. This aligns with community insights stating that target discovery relies entirely on these custom resources.

Option A is unlikely because quota limits typically generate explicit errors or warnings in the monitoring system or API responses, not silent absence of data. Option C is irrelevant; Grafana is a visualization tool and its presence does not affect metric collection by GMP. Option D is insufficient because while IAM permissions are necessary, the absence of the 'monitoring.servicesViewer' role would likely prevent access to existing metrics rather than causing new metrics to stop appearing without traceable errors during the collection phase itself. The most common cause for silent metric loss in GMP managed collection is misconfiguration in the PodMonitoring spec, particularly the port definition.