various: add internal health and runtime metrics

Signed-off-by: NotAShelf <raf@notashelf.dev>
Change-Id: Iae1dcf8495a00159d588c6e2344312f36a6a6964

internal/health/metrics.go

@@ -0,0 +1,56 @@
+package health
+
+import (
+	"time"
+
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/collectors"
+)
+
+// Holds health and runtime metrics for the watchdog process
+type Collector struct {
+	buildInfo prometheus.Gauge
+	startTime prometheus.Gauge
+}
+
+// Creates a health metrics collector with build metadata
+func NewCollector(version, commit, buildDate string) *Collector {
+	buildInfo := prometheus.NewGauge(prometheus.GaugeOpts{
+		Name: "watchdog_build_info",
+		Help: "Build metadata for the running watchdog instance",
+		ConstLabels: prometheus.Labels{
+			"version":    version,
+			"commit":     commit,
+			"build_date": buildDate,
+		},
+	})
+	buildInfo.Set(1)
+
+	startTime := prometheus.NewGauge(prometheus.GaugeOpts{
+		Name: "watchdog_start_time_seconds",
+		Help: "Unix timestamp of when the watchdog process started",
+	})
+	startTime.Set(float64(time.Now().Unix()))
+
+	return &Collector{
+		buildInfo: buildInfo,
+		startTime: startTime,
+	}
+}
+
+// Registers all health metrics plus Go runtime collectors
+func (c *Collector) Register(reg prometheus.Registerer) error {
+	if err := reg.Register(c.buildInfo); err != nil {
+		return err
+	}
+	if err := reg.Register(c.startTime); err != nil {
+		return err
+	}
+	if err := reg.Register(collectors.NewGoCollector()); err != nil {
+		return err
+	}
+	if err := reg.Register(collectors.NewProcessCollector(collectors.ProcessCollectorOpts{})); err != nil {
+		return err
+	}
+	return nil
+}