Add check runtime metric

main.go

@@ -74,7 +74,7 @@ func checkMonitors(config *Config) error {
 
 			// Track status metrics
 			Metrics.SetMonitorStatus(monitor.Name, monitor.IsUp())
-			Metrics.CountCheck(monitor.Name, success, hasAlert)
+			Metrics.CountCheck(monitor.Name, success, monitor.LastCheckMilliseconds(), hasAlert)
 
 			if alertNotice != nil {
 				return sendAlerts(config, monitor, alertNotice)
@@ -108,7 +108,7 @@ func main() {
 
 	// Serve metrics exporter, if specified
 	if ExportMetrics {
-		slog.Infof("Exporting metrics to Prometheus")
+		slog.Infof("Exporting metrics to Prometheus on port %d", MetricsPort)
 
 		go ServeMetrics()
 	}

metrics.go

@@ -19,6 +19,7 @@ import (
 type MinitorMetrics struct {
 	alertCount    *prometheus.CounterVec
 	checkCount    *prometheus.CounterVec
+	checkTime     *prometheus.GaugeVec
 	monitorStatus *prometheus.GaugeVec
 }
 
@@ -40,6 +41,13 @@ func NewMetrics() *MinitorMetrics {
 			},
 			[]string{"monitor", "status", "is_alert"},
 		),
+		checkTime: prometheus.NewGaugeVec(
+			prometheus.GaugeOpts{
+				Name: "minitor_check_milliseconds",
+				Help: "Time in miliseconds that a check ran for",
+			},
+			[]string{"monitor", "status"},
+		),
 		monitorStatus: prometheus.NewGaugeVec(
 			prometheus.GaugeOpts{
 				Name: "minitor_monitor_up_count",
@@ -52,6 +60,7 @@ func NewMetrics() *MinitorMetrics {
 	// Register newly created metrics
 	prometheus.MustRegister(metrics.alertCount)
 	prometheus.MustRegister(metrics.checkCount)
+	prometheus.MustRegister(metrics.checkTime)
 	prometheus.MustRegister(metrics.monitorStatus)
 
 	return metrics
@@ -68,7 +77,7 @@ func (metrics *MinitorMetrics) SetMonitorStatus(monitor string, isUp bool) {
 }
 
 // CountCheck counts the result of a particular Monitor check
-func (metrics *MinitorMetrics) CountCheck(monitor string, isSuccess bool, isAlert bool) {
+func (metrics *MinitorMetrics) CountCheck(monitor string, isSuccess bool, ms int64, isAlert bool) {
 	status := "failure"
 	if isSuccess {
 		status = "success"
@@ -82,6 +91,10 @@ func (metrics *MinitorMetrics) CountCheck(monitor string, isSuccess bool, isAler
 	metrics.checkCount.With(
 		prometheus.Labels{"monitor": monitor, "status": status, "is_alert": alertVal},
 	).Inc()
+
+	metrics.checkTime.With(
+		prometheus.Labels{"monitor": monitor, "status": status},
+	).Set(float64(ms))
 }
 
 // CountAlert counts an alert

monitor.go

@@ -25,6 +25,7 @@ type Monitor struct { //nolint:maligned
 	lastCheck         time.Time
 	lastSuccess       time.Time
 	lastOutput        string
+	lastCheckDuration time.Duration
 }
 
 // IsValid returns a boolean indicating if the Monitor has been correctly
@@ -57,9 +58,11 @@ func (monitor *Monitor) Check() (bool, *AlertNotice) {
 		cmd = ShellCommand(monitor.Command.ShellCommand)
 	}
 
+	checkStartTime := time.Now()
 	output, err := cmd.CombinedOutput()
 	monitor.lastCheck = time.Now()
 	monitor.lastOutput = string(output)
+	monitor.lastCheckDuration = monitor.lastCheck.Sub(checkStartTime)
 
 	var alertNotice *AlertNotice
 
@@ -88,6 +91,11 @@ func (monitor Monitor) IsUp() bool {
 	return monitor.alertCount == 0
 }
 
+// LastCheckMilliseconds gives number of miliseconds the last check ran for
+func (monitor Monitor) LastCheckMilliseconds() int64 {
+	return monitor.lastCheckDuration.Milliseconds()
+}
+
 func (monitor *Monitor) success() (notice *AlertNotice) {
 	if !monitor.IsUp() {
 		// Alert that we have recovered