The correct option is Alertmanager.

Prometheus evaluates custom health metrics against alerting rules and then sends firing alerts to Alertmanager. Alertmanager is the component that groups and silences alerts and routes them to notification receivers such as email, PagerDuty, or chat systems.

You author alerting rules in Prometheus or via the Prometheus Operator so that metrics crossing thresholds become alerts, and those alerts are managed and dispatched by Alertmanager.

Grafana is primarily a visualization and dashboarding tool. It can display metrics and it also offers alerting features, but it is not the standard component used to receive and centrally manage Prometheus alert notifications in the typical Prometheus architecture.

Cloud Monitoring is a cloud provider monitoring service and it may ingest metrics or provide its own alerting, but it is not the Prometheus alert routing and notification component that handles Prometheus alert delivery and silencing.

Fluentd is a log collection and forwarding agent and it is not used to evaluate metrics or manage alert notifications, so it is not the correct component for generating or routing Prometheus alerts.

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