Fix metrics export

Actually register the right prometheus Handler. Also make the server
wait for a metrics collection cycle to complete before starting the
HTTP server, so we never serve missing metrics.

exporter.go

@@ -5,7 +5,6 @@ import (
 	"bytes"
 	"flag"
 	"io"
-	"io/ioutil"
 	"log"
 	"net"
 	"net/http"
@@ -24,7 +23,17 @@ import (
 	"github.com/prometheus/client_golang/prometheus/promhttp"
 )
 
-var addr = flag.String("addr", ":3909", "address to listen on")
+var (
+	addr           = flag.String("addr", ":3909", "address to listen on")
+	updateInterval = flag.Duration("interval", 10*time.Second, "update interval")
+	doDebug        = flag.Bool("debug", false, "log debug messages")
+)
+
+func debug(s string, args ...interface{}) {
+	if *doDebug {
+		log.Printf(s, args...)
+	}
+}
 
 func splitServiceName(path string) (string, string) {
 	slice, name := filepath.Split(path)
@@ -82,13 +91,13 @@ func parseBlkioMapFile(path string) (map[string]int64, error) {
 	return result, scanner.Err()
 }
 
-func parseSingleValueFile(path string) (int64, error) {
-	data, err := ioutil.ReadFile(path)
-	if err != nil {
-		return 0, err
-	}
-	return strconv.ParseInt(string(data), 10, 64)
-}
+// func parseSingleValueFile(path string) (int64, error) {
+// 	data, err := ioutil.ReadFile(path)
+// 	if err != nil {
+// 		return 0, err
+// 	}
+// 	return strconv.ParseInt(string(data), 10, 64)
+// }
 
 func cgroupStatPath(cgroupPath, collector, path string) string {
 	return filepath.Join("/sys/fs/cgroup", collector, cgroupPath, path)
@@ -285,13 +294,13 @@ func walkCGroups() ([]prometheus.Metric, error) {
 }
 
 func walkCGroup(path string) ([]prometheus.Metric, error) {
-	log.Printf("found service %s", path)
+	debug("found service %s", path)
 
 	var metrics []prometheus.Metric
 	for _, s := range subsystems {
 		m, err := s.parse(path)
 		if err != nil {
-			log.Printf("service %s, subsystem %v: error: %v", path, s, err)
+			debug("service %s, subsystem %v: error: %v", path, s, err)
 			continue
 		}
 		metrics = append(metrics, m...)
@@ -306,6 +315,17 @@ func walkCGroup(path string) ([]prometheus.Metric, error) {
 type collector struct {
 	mx      sync.Mutex
 	metrics []prometheus.Metric
+	readyCh chan bool
+}
+
+func newCollector() *collector {
+	return &collector{
+		readyCh: make(chan bool),
+	}
+}
+
+func (c *collector) WaitReady() {
+	<-c.readyCh
 }
 
 func (c *collector) Describe(ch chan<- *prometheus.Desc) {
@@ -314,22 +334,30 @@ func (c *collector) Describe(ch chan<- *prometheus.Desc) {
 	}
 }
 
-func (c *collector) update(metrics []prometheus.Metric) {
-	c.mx.Lock()
-	c.metrics = metrics
-	c.mx.Unlock()
-}
-
 func (c *collector) Collect(ch chan<- prometheus.Metric) {
 	c.mx.Lock()
-	defer c.mx.Unlock()
+	count := 0
 	for _, m := range c.metrics {
 		ch <- m
+		count++
 	}
+	debug("collected %d metrics", count)
+	c.mx.Unlock()
+}
+
+func (c *collector) update(metrics []prometheus.Metric) {
+	c.mx.Lock()
+	c.metrics = metrics
+	c.mx.Unlock()
 }
 
 func (c *collector) loop(ctx context.Context) {
-	ticker := time.NewTicker(60 * time.Second)
+	if m, err := walkCGroups(); err == nil {
+		c.update(m)
+	}
+	close(c.readyCh)
+
+	ticker := time.NewTicker(*updateInterval)
 	defer ticker.Stop()
 	for {
 		select {
@@ -347,10 +375,25 @@ func main() {
 	log.SetFlags(0)
 	flag.Parse()
 
+	c := newCollector()
+	reg := prometheus.NewRegistry()
+	reg.MustRegister(c)
+
+	// Create a cancelable Context and cancel it when we receive a
+	// termination signal. This will stop the metrics updater.
+	ctx, cancel := context.WithCancel(context.Background())
+
+	// Run the update loop in a goroutine.
+	go c.loop(ctx)
+
+	// Only start the HTTP server if we have collected the first
+	// round of metrics.
+	c.WaitReady()
+
 	// Create a very simple HTTP server that only exposes the
 	// Prometheus metrics handler.
 	mux := http.NewServeMux()
-	mux.Handle("/metrics", promhttp.Handler())
+	mux.Handle("/metrics", promhttp.HandlerFor(reg, promhttp.HandlerOpts{}))
 	mux.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
 		if r.URL.Path == "/" {
 			io.WriteString(w, `<html>
@@ -375,10 +418,6 @@ func main() {
 		MaxHeaderBytes: 1 << 20,
 	}
 
-	// Create a cancelable Context and cancel it when we receive a
-	// termination signal. This will stop the metrics updater.
-	ctx, cancel := context.WithCancel(context.Background())
-
 	sigCh := make(chan os.Signal, 1)
 	go func() {
 		<-sigCh
@@ -387,12 +426,5 @@ func main() {
 	}()
 	signal.Notify(sigCh, syscall.SIGTERM, syscall.SIGINT)
 
-	// Run the update loop in a goroutine.
-	c := &collector{}
-	go c.loop(ctx)
-
-	reg := prometheus.NewRegistry()
-	reg.MustRegister(c)
-
 	log.Fatal(srv.Serve(l))
 }