metrics: Add server_version metric

etcdserver/metrics.go

@@ -18,6 +18,7 @@ import (
 	"time"
 
 	"github.com/coreos/etcd/pkg/runtime"
+	"github.com/coreos/etcd/version"
 	"github.com/prometheus/client_golang/prometheus"
 )
 
@@ -64,6 +65,13 @@ var (
 		Name:      "lease_expired_total",
 		Help:      "The total number of expired leases.",
 	})
+	currentVersion = prometheus.NewGaugeVec(prometheus.GaugeOpts{
+		Namespace: "etcd",
+		Subsystem: "server",
+		Name:      "version",
+		Help:      "Which version is running. 1 for 'server_version' label with current version.",
+	},
+		[]string{"server_version"})
 )
 
 func init() {
@@ -74,6 +82,11 @@ func init() {
 	prometheus.MustRegister(proposalsPending)
 	prometheus.MustRegister(proposalsFailed)
 	prometheus.MustRegister(leaseExpired)
+	prometheus.MustRegister(currentVersion)
+
+	currentVersion.With(prometheus.Labels{
+		"server_version": version.Version,
+	}).Set(1)
 }
 
 func monitorFileDescriptor(done <-chan struct{}) {