feat: Track the last time we updated the metrics

main.go

@@ -88,8 +88,9 @@ func (c *CertificateMetrics) checkTls() {
 	}
 }
 
-func updateMetrics(metrics *[]CertificateMetrics) {
+func updateMetrics(metrics *[]CertificateMetrics, lastUpdated prometheus.Gauge) {
 	log.Debugf("Updating metrics for %d domains...", len(*metrics))
+	lastUpdated.SetToCurrentTime()
 	for _, metric := range *metrics {
 		metric.checkTls()
 	}
@@ -108,6 +109,13 @@ func run(ctx *cli.Context) error {
 
 	// Setup metrics
 	registry := prometheus.NewRegistry()
+	lastUpdatedMetric := prometheus.NewGauge(
+		prometheus.GaugeOpts{
+			Name: "certs_status_last_updated",
+		},
+	)
+	registry.MustRegister(lastUpdatedMetric)
+
 	metrics := make([]CertificateMetrics, 0)
 	for _, d := range domains {
 		log.Debugf("Parsing '%s'...", d)
@@ -155,7 +163,7 @@ func run(ctx *cli.Context) error {
 		gocron.DurationJob(24*time.Hour),
 		gocron.NewTask(
 			func() {
-				updateMetrics(&metrics)
+				updateMetrics(&metrics, lastUpdatedMetric)
 			},
 		),
 	)
@@ -166,7 +174,7 @@ func run(ctx *cli.Context) error {
 
 	// Perform an initial run to populate the metrics
 	log.Info("Performing initial requests...")
-	updateMetrics(&metrics)
+	updateMetrics(&metrics, lastUpdatedMetric)
 	log.Debug("Done")
 
 	http.Handle(