Expose number of time unsee collected alerts from Alertmanager API

This way one can alert if unsee stops collecting alerts.

alertmanager/metrics.go

@@ -24,10 +24,18 @@ var (
 		},
 		[]string{"alertmanager", "endpoint"},
 	)
+	metricCollectRuns = prometheus.NewGaugeVec(
+		prometheus.GaugeOpts{
+			Name: "unsee_collect_cycles_total",
+			Help: "Total number of alert collection cycles run",
+		},
+		[]string{"alertmanager"},
+	)
 )
 
 func init() {
 	prometheus.MustRegister(metricAlerts)
 	prometheus.MustRegister(metricAlertGroups)
 	prometheus.MustRegister(metricAlertmanagerErrors)
+	prometheus.MustRegister(metricCollectRuns)
 }

alertmanager/models.go

@@ -264,6 +264,10 @@ func (am *Alertmanager) Pull() error {
 		return err
 	}
 
+	metricCollectRuns.With(prometheus.Labels{
+		"alertmanager": am.Name,
+	}).Inc()
+
 	am.lastError = ""
 	return nil
 }