s3store: Do not register metrics to default registry

cmd/tusd/cli/composer.go

@@ -5,6 +5,7 @@ import (
 	"path/filepath"
 	"strings"
 
+	"github.com/prometheus/client_golang/prometheus"
 	"github.com/tus/tusd/pkg/filelocker"
 	"github.com/tus/tusd/pkg/filestore"
 	"github.com/tus/tusd/pkg/gcsstore"
@@ -64,6 +65,10 @@ func CreateComposer() {
 
 		locker := memorylocker.New()
 		locker.UseIn(Composer)
+
+		// Attach the metrics from S3 store to the global Prometheus registry
+		// TODO: Do not use the global registry here.
+		store.RegisterMetrics(prometheus.DefaultRegisterer)
 	} else if Flags.GCSBucket != "" {
 		if Flags.GCSObjectPrefix != "" && strings.Contains(Flags.GCSObjectPrefix, "_") {
 			stderr.Fatalf("gcs-object-prefix value (%s) can't contain underscore. "+

pkg/s3store/s3store.go

@@ -207,8 +207,6 @@ func New(bucket string, service S3API) S3Store {
 		Help:       "Duration of requests sent to S3 in milliseconds per operation",
 		Objectives: map[float64]float64{0.5: 0.05, 0.9: 0.01, 0.99: 0.001},
 	}, []string{"operation"})
-	// TODO: Do not register them globally but to a specific prometheus handler
-	prometheus.MustRegister(requestDurationMetric)
 
 	return S3Store{
 		Bucket:                bucket,
@@ -239,6 +237,10 @@ func (store S3Store) UseIn(composer *handler.StoreComposer) {
 	composer.UseLengthDeferrer(store)
 }
 
+func (store S3Store) RegisterMetrics(registry prometheus.Registerer) {
+	registry.MustRegister(store.requestDurationMetric)
+}
+
 func (store S3Store) observeRequestDuration(start time.Time, label string) {
 	elapsed := time.Now().Sub(start)
 	ms := float64(elapsed.Nanoseconds() / int64(time.Millisecond))