Add tlsconmon component

stepmon/stepmon.go

@@ -62,6 +62,8 @@ func (sm *StepMonitor) Start() {
 	} else {
 		stepCertError.WithLabelValues(sm.RootID).Set(0)
 	}
+	secondsLeft := time.Until(sm.certificate.NotAfter).Seconds()
+	stepCertTimeLeft.WithLabelValues(sm.RootID).Set(secondsLeft)
 
 	timerCertFetch := time.NewTimer(5 * time.Minute)
 	defer timerCertFetch.Stop()
@@ -87,7 +89,6 @@ func (sm *StepMonitor) Start() {
 			timerUpdateMonitor.Reset(1 * time.Second)
 
 		case <-sm.shutdownCh:
-			close(sm.shutdownCh)
 			sm.shutdownComplete <- struct{}{}
 			return
 		}
@@ -96,6 +97,8 @@ func (sm *StepMonitor) Start() {
 
 func (sm *StepMonitor) Shutdown() error {
 	sm.shutdownCh <- struct{}{}
+	close(sm.shutdownCh)
+
 	<-sm.shutdownComplete
 	close(sm.shutdownComplete)
 	sm.logger.Info("Monitoring stopped")