Add build_info metric similar to the one of Prometheus itself

Makefile

@@ -13,6 +13,16 @@
 
 VERSION  := 0.12.0rc1
 TARGET   := node_exporter
-GOFLAGS  := -ldflags "-X main.Version=$(VERSION)"
+
+REVISION := $(shell git rev-parse --short HEAD 2> /dev/null || echo 'unknown')
+BRANCH   := $(shell git rev-parse --abbrev-ref HEAD 2> /dev/null || echo 'unknown')
+
+REPO_PATH := "github.com/prometheus/node_exporter"
+LDFLAGS   := -X main.Version=$(VERSION)
+LDFLAGS   += -X $(REPO_PATH)/collector.Version=$(VERSION)
+LDFLAGS   += -X $(REPO_PATH)/collector.Revision=$(REVISION)
+LDFLAGS   += -X $(REPO_PATH)/collector.Branch=$(BRANCH)
+
+GOFLAGS   := -ldflags "$(LDFLAGS)"
 
 include Makefile.COMMON

collector/version.go

@@ -0,0 +1,51 @@
+// Copyright 2015 The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package collector
+
+import (
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+var (
+	Version  string
+	Revision string
+	Branch   string
+)
+
+type versionCollector struct {
+	metric *prometheus.GaugeVec
+}
+
+func init() {
+	Factories["version"] = NewVersionCollector
+}
+
+func NewVersionCollector() (Collector, error) {
+	metric := prometheus.NewGaugeVec(
+		prometheus.GaugeOpts{
+			Name: "node_exporter_build_info",
+			Help: "A metric with a constant '1' value labeled by version, revision, and branch from which the node_exporter was built.",
+		},
+		[]string{"version", "revision", "branch"},
+	)
+	metric.WithLabelValues(Version, Revision, Branch).Set(1)
+	return &versionCollector{
+		metric: metric,
+	}, nil
+}
+
+func (c *versionCollector) Update(ch chan<- prometheus.Metric) (err error) {
+	c.metric.Collect(ch)
+	return err
+}

node_exporter.go

@@ -42,7 +42,7 @@ var (
 	listenAddress     = flag.String("web.listen-address", ":9100", "Address on which to expose metrics and web interface.")
 	metricsPath       = flag.String("web.telemetry-path", "/metrics", "Path under which to expose metrics.")
 	enabledCollectors = flag.String("collectors.enabled",
-		filterAvailableCollectors("conntrack,diskstats,filefd,filesystem,loadavg,mdadm,meminfo,netdev,netstat,sockstat,stat,textfile,time,uname"),
+		filterAvailableCollectors("conntrack,diskstats,filefd,filesystem,loadavg,mdadm,meminfo,netdev,netstat,sockstat,stat,textfile,time,uname,version"),
 		"Comma-separated list of collectors to use.")
 	printCollectors = flag.Bool("collectors.print", false, "If true, print available collectors and exit.")