Prometheus Alertmanager and YAML: Label-based Grouping for Noise Reduction

Managing notification volume in Prometheus Alertmanager requires a precise configuration of the group_by key within the YAML configuration file. This feature determines how alerts are aggregated into single notifications based on shared labels, preventing alert fatigue during large-scale incidents.

When defining these groups, there is a design tension between grouping by broad labels (e.g., cluster) to minimize noise and grouping by granular labels (e.g., instance or severity) to ensure visibility of distinct issues. Misconfiguration can lead to unrelated alerts being bundled together, potentially masking critical failures.

Given the runtime evaluation of these labels in recent Alertmanager versions, what are the best practices for structuring group_by to balance notification density with alert granularity? How does the inclusion of high-cardinality labels in the grouping logic impact the effectiveness of group_interval and repeat_interval settings?