prometheus: expose zrepl version as const metric

daemon/daemon.go

@@ -95,6 +95,7 @@ func Run(ctx context.Context, conf *config.Config) error {
 	}
 
 	// register global (=non job-local) metrics
+	version.PrometheusRegister(prometheus.DefaultRegisterer)
 	zfscmd.RegisterMetrics(prometheus.DefaultRegisterer)
 	trace.RegisterMetrics(prometheus.DefaultRegisterer)
 	endpoint.RegisterMetrics(prometheus.DefaultRegisterer)

version/version.go

@@ -3,6 +3,8 @@ package version
 import (
 	"fmt"
 	"runtime"
+
+	"github.com/prometheus/client_golang/prometheus"
 )
 
 var (
@@ -29,3 +31,21 @@ func (i *ZreplVersionInformation) String() string {
 	return fmt.Sprintf("zrepl version=%s GOOS=%s GOARCH=%s Compiler=%s",
 		i.Version, i.RuntimeGOOS, i.RuntimeGOARCH, i.RUNTIMECompiler)
 }
+
+var prometheusMetric = prometheus.NewUntypedFunc(
+	prometheus.UntypedOpts{
+		Namespace: "zrepl",
+		Subsystem: "version",
+		Name:      "daemon",
+		Help:      "zrepl daemon version",
+		ConstLabels: map[string]string{
+			"raw":          zreplVersion,
+			"version_info": NewZreplVersionInformation().String(),
+		},
+	},
+	func() float64 { return 1 },
+)
+
+func PrometheusRegister(r prometheus.Registerer) {
+	r.MustRegister(prometheusMetric)
+}