export config file hash in a metric (#3768)

Signed-off-by: zounengren <zounengren@cmss.chinamobile.com>

4 files changed, 19 insertions, 3 deletions

diff --git a/plugin/reload/README.md b/plugin/reload/README.md
index 8e58d1e73..9809cdbaa 100644
--- a/plugin/reload/README.md
+++ b/plugin/reload/README.md
@@ -99,6 +99,9 @@ CoreDNS v1.7.0 and later does parse the Corefile and supports detecting changes
  If monitoring is enabled (via the *prometheus* plugin) then the following metric is exported:
 
 * `coredns_reload_failed_count_total{}` - counts the number of failed reload attempts.
+* `coredns_reload_version_info{hash, value}` - record the hash value during reload.
+
+Currently the type of `hash` is "md5", the `value` is the returned hash value.
 
 ## Also See
 
diff --git a/plugin/reload/metrics.go b/plugin/reload/metrics.go
index 1f790d4c1..de46862a4 100644
--- a/plugin/reload/metrics.go
+++ b/plugin/reload/metrics.go
@@ -14,4 +14,11 @@ var (
 		Name:      "failed_count_total",
 		Help:      "Counter of the number of failed reload attempts.",
 	})
+
+	reloadInfo = prometheus.NewGaugeVec(prometheus.GaugeOpts{
+		Namespace: plugin.Namespace,
+		Subsystem: "reload",
+		Name:      "version_info",
+		Help:      "A metric with a constant '1' value labeled by hash, and value which type of hash generated.",
+	}, []string{"hash", "value"})
 )
diff --git a/plugin/reload/reload.go b/plugin/reload/reload.go
index 817582c8c..0b58d2a8e 100644
--- a/plugin/reload/reload.go
+++ b/plugin/reload/reload.go
@@ -4,12 +4,14 @@ package reload
 import (
 	"bytes"
 	"crypto/md5"
+	"encoding/hex"
 	"encoding/json"
 	"sync"
 	"time"
 
 	"github.com/caddyserver/caddy"
 	"github.com/caddyserver/caddy/caddyfile"
+	"github.com/prometheus/client_golang/prometheus"
 )
 
 const (
@@ -61,7 +63,6 @@ func hook(event caddy.EventName, info interface{}) error {
 	if event != caddy.InstanceStartupEvent {
 		return nil
 	}
-
 	// if reload is removed from the Corefile, then the hook
 	// is still registered but setup is never called again
 	// so we need a flag to tell us not to reload
@@ -96,12 +97,14 @@ func hook(event caddy.EventName, info interface{}) error {
 				}
 				s := md5.Sum(parsedCorefile)
 				if s != md5sum {
+					reloadInfo.Delete(prometheus.Labels{"hash": "md5", "value": hex.EncodeToString(md5sum[:])})
 					// Let not try to restart with the same file, even though it is wrong.
 					md5sum = s
 					// now lets consider that plugin will not be reload, unless appear in next config file
 					// change status of usage will be reset in setup if the plugin appears in config file
 					r.setUsage(maybeUsed)
 					_, err := instance.Restart(corefile)
+					reloadInfo.WithLabelValues("md5", hex.EncodeToString(md5sum[:])).Set(1)
 					if err != nil {
 						log.Errorf("Corefile changed but reload failed: %s", err)
 						FailedCount.Add(1)
diff --git a/plugin/reload/setup.go b/plugin/reload/setup.go
index c0dcc14e9..b0ba3e1c4 100644
--- a/plugin/reload/setup.go
+++ b/plugin/reload/setup.go
@@ -7,6 +7,7 @@ import (
 	"time"
 
 	"github.com/coredns/coredns/plugin"
+	"github.com/coredns/coredns/plugin/metrics"
 	clog "github.com/coredns/coredns/plugin/pkg/log"
 
 	"github.com/caddyserver/caddy"
@@ -67,11 +68,13 @@ func setup(c *caddy.Controller) error {
 	// prepare info for next onInstanceStartup event
 	r.setInterval(i)
 	r.setUsage(used)
-
 	once.Do(func() {
 		caddy.RegisterEventHook("reload", hook)
+		c.OnRestart(func() error {
+			metrics.MustRegister(c, reloadInfo)
+			return nil
+		})
 	})
-
 	// re-register on finalShutDown as the instance most-likely will be changed
 	shutOnce.Do(func() {
 		c.OnFinalShutdown(func() error {