receive: Store the most recent config hash and timestamp as metrics

pkg/receive/config.go

@@ -2,6 +2,8 @@ package receive
 
 import (
 	"context"
+	"crypto/md5"
+	"encoding/binary"
 	"encoding/json"
 	"io/ioutil"
 	"os"
@@ -33,6 +35,9 @@ type ConfigWatcher struct {
 	logger   log.Logger
 	watcher  *fsnotify.Watcher
 
+	hashGauge            prometheus.Gauge
+	successGauge         prometheus.Gauge
+	lastSuccessTimeGauge prometheus.Gauge
 	changesCounter       prometheus.Counter
 	errorCounter         prometheus.Counter
 	refreshCounter       prometheus.Counter
@@ -62,6 +67,21 @@ func NewConfigWatcher(logger log.Logger, r prometheus.Registerer, path string, i
 		interval: time.Duration(interval),
 		logger:   logger,
 		watcher:  watcher,
+		hashGauge: prometheus.NewGauge(
+			prometheus.GaugeOpts{
+				Name: "thanos_receive_config_hash",
+				Help: "Hash of the currently loaded hashring configuration file.",
+			}),
+		successGauge: prometheus.NewGauge(
+			prometheus.GaugeOpts{
+				Name: "thanos_receive_config_last_reload_successful",
+				Help: "Whether the last hashring configuration file reload attempt was successful.",
+			}),
+		lastSuccessTimeGauge: prometheus.NewGauge(
+			prometheus.GaugeOpts{
+				Name: "thanos_receive_config_last_reload_success_timestamp_seconds",
+				Help: "Timestamp of the last successful hashring configuration file reload.",
+			}),
 		changesCounter: prometheus.NewCounter(
 			prometheus.CounterOpts{
 				Name: "thanos_receive_hashrings_file_changes_total",
@@ -93,6 +113,9 @@ func NewConfigWatcher(logger log.Logger, r prometheus.Registerer, path string, i
 
 	if r != nil {
 		r.MustRegister(
+			c.hashGauge,
+			c.successGauge,
+			c.lastSuccessTimeGauge,
 			c.changesCounter,
 			c.errorCounter,
 			c.refreshCounter,
@@ -148,8 +171,13 @@ func (cw *ConfigWatcher) Run(ctx context.Context) {
 	}
 }
 
-// readFile reads the configured file and returns a configuration.
-func (cw *ConfigWatcher) readFile() ([]HashringConfig, error) {
+// C returns a chan that gets hashring configuration updates.
+func (cw *ConfigWatcher) C() <-chan []HashringConfig {
+	return cw.ch
+}
+
+// readFile reads the configured file and returns content of configuration file.
+func (cw *ConfigWatcher) readFile() ([]byte, error) {
 	fd, err := os.Open(cw.path)
 	if err != nil {
 		return nil, err
@@ -160,33 +188,43 @@ func (cw *ConfigWatcher) readFile() ([]HashringConfig, error) {
 		}
 	}()
 
-	content, err := ioutil.ReadAll(fd)
-	if err != nil {
-		return nil, err
-	}
+	return ioutil.ReadAll(fd)
+}
 
+// loadConfig loads raw configuration content and returns a configuration.
+func (cw *ConfigWatcher) loadConfig(content []byte) ([]HashringConfig, error) {
 	var config []HashringConfig
-	err = json.Unmarshal(content, &config)
+	err := json.Unmarshal(content, &config)
 	return config, err
 }
 
 // refresh reads the configured file and sends the hashring configuration on the channel.
 func (cw *ConfigWatcher) refresh(ctx context.Context) {
 	cw.refreshCounter.Inc()
-	config, err := cw.readFile()
+	cfgContent, err := cw.readFile()
 	if err != nil {
 		cw.errorCounter.Inc()
 		level.Error(cw.logger).Log("msg", "failed to read configuration file", "err", err, "path", cw.path)
 		return
 	}
 
+	config, err := cw.loadConfig(cfgContent)
+	if err != nil {
+		cw.errorCounter.Inc()
+		level.Error(cw.logger).Log("msg", "failed to load configuration file", "err", err, "path", cw.path)
+		return
+	}
+
 	// If there was no change to the configuration, return early.
 	if reflect.DeepEqual(cw.last, config) {
 		return
 	}
 	cw.changesCounter.Inc()
 	// Save the last known configuration.
 	cw.last = config
+	cw.successGauge.Set(1)
+	cw.lastSuccessTimeGauge.Set(float64(time.Now().Unix()))
+	cw.hashGauge.Set(hashAsMetricValue(cfgContent))
 
 	for _, c := range config {
 		cw.hashringNodesGauge.WithLabelValues(c.Hashring).Set(float64(len(c.Endpoints)))
@@ -228,7 +266,12 @@ func (cw *ConfigWatcher) stop() {
 	level.Debug(cw.logger).Log("msg", "hashring configuration watcher stopped")
 }
 
-// C returns a chan that gets hashring configuration updates.
-func (cw *ConfigWatcher) C() <-chan []HashringConfig {
-	return cw.ch
+// hashAsMetricValue generates metric value from hash of data.
+func hashAsMetricValue(data []byte) float64 {
+	sum := md5.Sum(data)
+	// We only want 48 bits as a float64 only has a 53 bit mantissa.
+	smallSum := sum[0:6]
+	var bytes = make([]byte, 8)
+	copy(bytes, smallSum)
+	return float64(binary.LittleEndian.Uint64(bytes))
 }