Add coredns_build_info metric (#1418)

In order to track the rollout status of CoreDNS versions, add the common
build_info metric.

6 files changed, 25 insertions, 8 deletions

diff --git a/Makefile b/Makefile
index 0b01b0bc2..919402595 100644
--- a/Makefile
+++ b/Makefile
@@ -9,7 +9,7 @@ all: coredns
 
 .PHONY: coredns
 coredns: $(CHECKS)
-	CGO_ENABLED=0 $(SYSTEM) go build $(VERBOSE) -ldflags="-s -w -X github.com/coredns/coredns/coremain.gitCommit=$(GITCOMMIT)" -o $(BINARY)
+	CGO_ENABLED=0 $(SYSTEM) go build $(VERBOSE) -ldflags="-s -w -X github.com/coredns/coredns/coremain.GitCommit=$(GITCOMMIT)" -o $(BINARY)
 
 .PHONY: check
 check: linter core/zplugin.go core/dnsserver/zdirectives.go godeps
diff --git a/Makefile.release b/Makefile.release
index 37c6294a8..4b64e55ec 100644
--- a/Makefile.release
+++ b/Makefile.release
@@ -53,7 +53,7 @@ endif
 
 DOCKER:=
 NAME:=coredns
-VERSION:=$(shell grep 'coreVersion' coremain/version.go | awk '{ print $$3 }' | tr -d '"')
+VERSION:=$(shell grep 'CoreVersion' coremain/version.go | awk '{ print $$3 }' | tr -d '"')
 GITHUB:=coredns
 DOCKER_IMAGE_NAME:=$(DOCKER)/$(NAME)
 GITCOMMIT:=$(shell git describe --dirty --always)
diff --git a/coremain/run.go b/coremain/run.go
index 69ecb6b59..61d2e24be 100644
--- a/coremain/run.go
+++ b/coremain/run.go
@@ -49,7 +49,7 @@ func init() {
 	caddy.SetDefaultCaddyfileLoader("default", caddy.LoaderFunc(defaultLoader))
 
 	caddy.AppName = coreName
-	caddy.AppVersion = coreVersion
+	caddy.AppVersion = CoreVersion
 }
 
 // Run is CoreDNS's main() function.
@@ -180,7 +180,7 @@ func versionString() string {
 // e.g.,
 // linux/amd64, go1.8.3, a6d2d7b5
 func releaseString() string {
-	return fmt.Sprintf("%s/%s, %s, %s\n", runtime.GOOS, runtime.GOARCH, runtime.Version(), gitCommit)
+	return fmt.Sprintf("%s/%s, %s, %s\n", runtime.GOOS, runtime.GOARCH, runtime.Version(), GitCommit)
 }
 
 // setVersion figures out the version information
@@ -193,7 +193,7 @@ func setVersion() {
 	if gitNearestTag != "" || gitTag != "" {
 		if devBuild && gitNearestTag != "" {
 			appVersion = fmt.Sprintf("%s (+%s %s)",
-				strings.TrimPrefix(gitNearestTag, "v"), gitCommit, buildDate)
+				strings.TrimPrefix(gitNearestTag, "v"), GitCommit, buildDate)
 		} else if gitTag != "" {
 			appVersion = strings.TrimPrefix(gitTag, "v")
 		}
@@ -252,7 +252,7 @@ var (
 	buildDate        string // date -u
 	gitTag           string // git describe --exact-match HEAD 2> /dev/null
 	gitNearestTag    string // git describe --abbrev=0 --tags HEAD
-	gitCommit        string // git rev-parse HEAD
+	GitCommit        string // git rev-parse HEAD
 	gitShortStat     string // git diff-index --shortstat
 	gitFilesModified string // git diff-index --name-only HEAD
 )
diff --git a/coremain/version.go b/coremain/version.go
index fbf0ed97b..93d6380e0 100644
--- a/coremain/version.go
+++ b/coremain/version.go
@@ -1,8 +1,9 @@
 package coremain
 
 const (
-	coreName    = "CoreDNS"
-	coreVersion = "1.0.4"
+	coreName = "CoreDNS"
+	// CoreVersion is the current version of CoreDNS.
+	CoreVersion = "1.0.4"
 
 	serverType = "dns"
 )
diff --git a/plugin/metrics/README.md b/plugin/metrics/README.md
index b14628675..4a27dfdf6 100644
--- a/plugin/metrics/README.md
+++ b/plugin/metrics/README.md
@@ -10,6 +10,7 @@ With *prometheus* you export metrics from CoreDNS and any plugin that has them.
 The default location for the metrics is `localhost:9153`. The metrics path is fixed to `/metrics`.
 The following metrics are exported:
 
+* `coredns_build_info{version, revision, goversion}` - info about CoreDNS itself.
 * `coredns_dns_request_count_total{zone, proto, family}` - total query count.
 * `coredns_dns_request_duration_seconds{zone}` - duration to process each query.
 * `coredns_dns_request_size_bytes{zone, proto}` - size of the request in bytes.
diff --git a/plugin/metrics/metrics.go b/plugin/metrics/metrics.go
index 70f82a664..25d6da488 100644
--- a/plugin/metrics/metrics.go
+++ b/plugin/metrics/metrics.go
@@ -6,8 +6,10 @@ import (
 	"net"
 	"net/http"
 	"os"
+	"runtime"
 	"sync"
 
+	"github.com/coredns/coredns/coremain"
 	"github.com/coredns/coredns/plugin"
 	"github.com/coredns/coredns/plugin/metrics/vars"
 	"github.com/prometheus/client_golang/prometheus"
@@ -39,6 +41,7 @@ func New(addr string) *Metrics {
 	met.MustRegister(prometheus.NewProcessCollector(os.Getpid(), ""))
 
 	// Add all of our collectors
+	met.MustRegister(buildInfo)
 	met.MustRegister(vars.RequestCount)
 	met.MustRegister(vars.RequestDuration)
 	met.MustRegister(vars.RequestSize)
@@ -46,6 +49,10 @@ func New(addr string) *Metrics {
 	met.MustRegister(vars.RequestType)
 	met.MustRegister(vars.ResponseSize)
 	met.MustRegister(vars.ResponseRcode)
+
+	// Initialize metrics.
+	buildInfo.WithLabelValues(coremain.CoreVersion, coremain.GitCommit, runtime.Version()).Set(1)
+
 	return met
 }
 
@@ -115,3 +122,11 @@ func keys(m map[string]bool) []string {
 // ListenAddr is assigned the address of the prometheus listener. Its use is mainly in tests where
 // we listen on "localhost:0" and need to retrieve the actual address.
 var ListenAddr string
+
+var (
+	buildInfo = prometheus.NewGaugeVec(prometheus.GaugeOpts{
+		Namespace: plugin.Namespace,
+		Name:      "build_info",
+		Help:      "A metric with a constant '1' value labeled by version, revision, and goversion from which CoreDNS was built.",
+	}, []string{"version", "revision", "goversion"})
+)