From 3a49a9343800c1d9b1686643b52ed2ac82ca5585 Mon Sep 17 00:00:00 2001
From: cpanato <ctadeu@gmail.com>
Date: Fri, 23 Sep 2022 17:18:55 +0200
Subject: [PATCH] export rekor build/version information

Signed-off-by: cpanato <ctadeu@gmail.com>
---
 cmd/rekor-server/app/root.go  |  2 +-
 cmd/rekor-server/app/serve.go |  4 ++++
 pkg/api/metrics.go            | 24 ++++++++++++++++++++++++
 3 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/cmd/rekor-server/app/root.go b/cmd/rekor-server/app/root.go
index 0d10b2f38..df8eea269 100644
--- a/cmd/rekor-server/app/root.go
+++ b/cmd/rekor-server/app/root.go
@@ -76,7 +76,7 @@ func init() {
 
 	rootCmd.PersistentFlags().String("rekor_server.signer", "memory",
 		`Rekor signer to use. Valid options are: [gcpkms, memory, filename containing PEM encoded private key].
-		Memory and file-based signers should only be used for testing.`)
+Memory and file-based signers should only be used for testing.`)
 	rootCmd.PersistentFlags().String("rekor_server.signer-passwd", "", "Password to decrypt signer private key")
 
 	rootCmd.PersistentFlags().Uint16("port", 3000, "Port to bind to")
diff --git a/cmd/rekor-server/app/serve.go b/cmd/rekor-server/app/serve.go
index 240b64183..bbad87b9c 100644
--- a/cmd/rekor-server/app/serve.go
+++ b/cmd/rekor-server/app/serve.go
@@ -21,6 +21,7 @@ import (
 	"time"
 
 	"github.com/go-openapi/loads"
+	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/client_golang/prometheus/promhttp"
 	"github.com/spf13/cobra"
 	"github.com/spf13/viper"
@@ -74,6 +75,9 @@ var serveCmd = &cobra.Command{
 		}
 		log.Logger.Infof("starting rekor-server @ %v", viStr)
 
+		reg := prometheus.NewRegistry()
+		reg.MustRegister(api.NewVersionCollector("rekor", vi))
+
 		doc, _ := loads.Embedded(restapi.SwaggerJSON, restapi.FlatSwaggerJSON)
 		server := restapi.NewServer(operations.NewRekorServerAPI(doc))
 		defer func() {
diff --git a/pkg/api/metrics.go b/pkg/api/metrics.go
index b22731f1b..ef11aab3a 100644
--- a/pkg/api/metrics.go
+++ b/pkg/api/metrics.go
@@ -16,10 +16,12 @@
 package api
 
 import (
+	"fmt"
 	"time"
 
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/client_golang/prometheus/promauto"
+	"sigs.k8s.io/release-utils/version"
 )
 
 var (
@@ -52,3 +54,25 @@ var (
 		Help: "Api QPS by path, method, and response code",
 	}, []string{"path", "method", "code"})
 )
+
+// NewVersionCollector returns a collector that exports metrics about current version
+// information.
+func NewVersionCollector(program string, versionInfo version.Info) prometheus.Collector {
+	return promauto.NewGaugeFunc(
+		prometheus.GaugeOpts{
+			Namespace: program,
+			Name:      "build_info",
+			Help: fmt.Sprintf(
+				"A metric with a constant '1' value labeled by version, revision, branch, and goversion from which %s was built.",
+				program,
+			),
+			ConstLabels: prometheus.Labels{
+				"version":    versionInfo.GitVersion,
+				"revision":   versionInfo.GitCommit,
+				"build_date": versionInfo.BuildDate,
+				"goversion":  versionInfo.GoVersion,
+			},
+		},
+		func() float64 { return 1 },
+	)
+}