Prometheus support (#450)

Co-authored-by: nils måsén <nils@piksel.se>
Co-authored-by: MihailITPlace <ya.halo-halo@yandex.ru>
Co-authored-by: Sebastiaan Tammer <sebastiaantammer@gmail.com>

pkg/metrics/metrics.go

@@ -0,0 +1,91 @@
+package metrics
+
+import (
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promauto"
+)
+
+var metrics *Metrics
+
+// Metric is the data points of a single scan
+type Metric struct {
+	Scanned int
+	Updated int
+	Failed  int
+}
+
+// Metrics is the handler processing all individual scan metrics
+type Metrics struct {
+	channel chan *Metric
+	scanned prometheus.Gauge
+	updated prometheus.Gauge
+	failed  prometheus.Gauge
+	total   prometheus.Counter
+	skipped prometheus.Counter
+}
+
+// Register registers metrics for an executed scan
+func (metrics *Metrics) Register(metric *Metric) {
+	metrics.channel <- metric
+}
+
+// Default creates a new metrics handler if none exists, otherwise returns the existing one
+func Default() *Metrics {
+	if metrics != nil {
+		return metrics
+	}
+
+	metrics = &Metrics{
+		scanned: promauto.NewGauge(prometheus.GaugeOpts{
+			Name: "watchtower_containers_scanned",
+			Help: "Number of containers scanned for changes by watchtower during the last scan",
+		}),
+		updated: promauto.NewGauge(prometheus.GaugeOpts{
+			Name: "watchtower_containers_updated",
+			Help: "Number of containers updated by watchtower during the last scan",
+		}),
+		failed: promauto.NewGauge(prometheus.GaugeOpts{
+			Name: "watchtower_containers_failed",
+			Help: "Number of containers where update failed during the last scan",
+		}),
+		total: promauto.NewCounter(prometheus.CounterOpts{
+			Name: "watchtower_scans_total",
+			Help: "Number of scans since the watchtower started",
+		}),
+		skipped: promauto.NewCounter(prometheus.CounterOpts{
+			Name: "watchtower_scans_skipped",
+			Help: "Number of skipped scans since watchtower started",
+		}),
+		channel: make(chan *Metric, 10),
+	}
+
+	go metrics.HandleUpdate(metrics.channel)
+
+	return metrics
+}
+
+// RegisterScan fetches a metric handler and enqueues a metric
+func RegisterScan(metric *Metric) {
+	metrics := Default()
+	metrics.Register(metric)
+}
+
+// HandleUpdate dequeue the metric channel and processes it
+func (metrics *Metrics) HandleUpdate(channel <-chan *Metric) {
+	for change := range channel {
+		if change == nil {
+			// Update was skipped and rescheduled
+			metrics.total.Inc()
+			metrics.skipped.Inc()
+			metrics.scanned.Set(0)
+			metrics.updated.Set(0)
+			metrics.failed.Set(0)
+			continue
+		}
+		// Update metrics with the new values
+		metrics.total.Inc()
+		metrics.scanned.Set(float64(change.Scanned))
+		metrics.updated.Set(float64(change.Updated))
+		metrics.failed.Set(float64(change.Failed))
+	}
+}