feat: new Prometheus metrics build_info (#3144)

Signed-off-by: Nicolas Lamirault <nicolas.lamirault@gmail.com>

metrics/metrics.go

@@ -3,13 +3,15 @@ package metrics
 import (
 	"context"
 	"net/http"
+	"runtime"
 
 	"github.com/prometheus/client_golang/prometheus/collectors"
 
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/client_golang/prometheus/promhttp"
 	"go.uber.org/zap"
 
+	argoevents "github.com/argoproj/argo-events"
 	"github.com/argoproj/argo-events/common/logging"
 )
 
@@ -23,6 +25,16 @@ const (
 	labelTriggerName     = "trigger_name"
 )
 
+var (
+	buildInfo = prometheus.NewGaugeVec(
+		prometheus.GaugeOpts{
+			Name: "build_info",
+			Help: "A metric with a constant '1' value labeled by version from which Argo-Events was built.",
+		},
+		[]string{"version", "goversion", "goarch", "commit"},
+	)
+)
+
 // Metrics represents EventSource metrics information
 type Metrics struct {
 	namespace               string
@@ -170,10 +182,19 @@ func (m *Metrics) Run(ctx context.Context, addr string) {
 	log := logging.FromContext(ctx)
 	metricsRegistry := prometheus.NewRegistry()
 	metricsRegistry.MustRegister(collectors.NewGoCollector(), m)
+	metricsRegistry.MustRegister(buildInfo)
+	recordBuildInfo()
+
 	http.Handle("/metrics", promhttp.HandlerFor(metricsRegistry, promhttp.HandlerOpts{}))
 
 	log.Info("starting metrics server")
 	if err := http.ListenAndServe(addr, nil); err != nil {
 		log.Fatalw("failed to start metrics server", zap.Error(err))
 	}
 }
+
+// recordBuildInfo publishes information about Argo-Rollouts version and runtime info through an info metric (gauge).
+func recordBuildInfo() {
+	vers := argoevents.GetVersion()
+	buildInfo.WithLabelValues(vers.Version, runtime.Version(), runtime.GOARCH, vers.GitCommit).Set(1)
+}