Add lifetime to certificates monitored

stepmon/stepmon.go

@@ -29,6 +29,13 @@ var stepCertError = promauto.NewGaugeVec(prometheus.GaugeOpts{
 	Help:      "Error checking the certificate.",
 }, []string{"cert_id"})
 
+var stepCertLifetime = promauto.NewGaugeVec(prometheus.GaugeOpts{
+	Namespace: "labmon",
+	Subsystem: "stepmon",
+	Name:      "certificate_lifetime_seconds",
+	Help:      "How long the certificate is valid in seconds.",
+}, []string{"cert_id"})
+
 type StepMonitor struct {
 	BaseURL string
 	RootID  string
@@ -77,6 +84,8 @@ func (sm *StepMonitor) Start() {
 				stepCertError.WithLabelValues(sm.RootID).Set(1)
 			} else {
 				stepCertError.WithLabelValues(sm.RootID).Set(0)
+				lifetime := sm.certificate.NotAfter.Sub(sm.certificate.NotBefore).Seconds()
+				stepCertLifetime.WithLabelValues(sm.RootID).Set(lifetime)
 			}
 
 			timerCertFetch.Reset(5 * time.Minute)