cmd/registry/config-dev.yml

@@ -31,7 +31,10 @@ storage:
 http:
     addr: :5000
     debug:
-        addr: localhost:5001
+        addr: :5001
+        prometheus:
+            enabled: true
+            path: /metrics
     headers:
         X-Content-Type-Options: [nosniff]
 redis:

configuration/configuration.go

@@ -133,6 +133,11 @@ type Configuration struct {
 		Debug struct {
 			// Addr specifies the bind address for the debug server.
 			Addr string `yaml:"addr,omitempty"`
+			// Prometheus configures the Prometheus telemetry endpoint.
+			Prometheus struct {
+				Enabled bool   `yaml:"enabled,omitempty"`
+				Path    string `yaml:"path,omitempty"`
+			} `yaml:"prometheus,omitempty"`
 		} `yaml:"debug,omitempty"`
 		// HTTP2 configuration options

configuration/configuration_test.go

@@ -85,7 +85,11 @@ var configStruct = Configuration{
 		} `yaml:"tls,omitempty"`
 		Headers http.Header `yaml:"headers,omitempty"`
 		Debug   struct {
-			Addr string `yaml:"addr,omitempty"`
+			Addr       string `yaml:"addr,omitempty"`
+			Prometheus struct {
+				Enabled bool   `yaml:"enabled,omitempty"`
+				Path    string `yaml:"path,omitempty"`
+			} `yaml:"prometheus,omitempty"`
 		} `yaml:"debug,omitempty"`
 		HTTP2 struct {
 			Disabled bool `yaml:"disabled,omitempty"`

docs/configuration.md

@@ -218,6 +218,9 @@ http:
       hosts: [myregistryaddress.org]
   debug:
     addr: localhost:5001
+    prometheus:
+      enabled: true
+      path: /metrics
   headers:
     X-Content-Type-Options: [nosniff]
   http2:
@@ -805,6 +808,19 @@ access to the debug endpoint is locked down in a production environment.
 The `debug` section takes a single required `addr` parameter, which specifies
 the `HOST:PORT` on which the debug server should accept connections.
+## `prometheus`
+
+The `prometheus` option defines whether the prometheus metrics is enable, as well
+as the path to access the metrics.
+
+| Parameter | Required | Description                                           |
+|-----------|----------|-------------------------------------------------------|
+| `enabled` | no       | Set `true` to enable the prometheus server            |
+| `path`    | no       | The path to access the metrics, `/metrics` by default |
+
+The url to access the metrics is `HOST:PORT/path`, where `HOST:PORT` is defined
+in `addr` under `debug`.
+
 ### `headers`
 The `headers` option is **optional** . Use it to specify headers that the HTTP

metrics/prometheus.go

+package metrics
+
+import "github.com/docker/go-metrics"
+
+const (
+	// NamespacePrefix is the namespace of prometheus metrics
+	NamespacePrefix = "registry"
+)
+
+var (
+	// StorageNamespace is the prometheus namespace of blob/cache related operations
+	StorageNamespace = metrics.NewNamespace(NamespacePrefix, "storage", nil)
+)

registry/handlers/app.go

@@ -20,6 +20,7 @@ import (
 	dcontext "github.com/docker/distribution/context"
 	"github.com/docker/distribution/health"
 	"github.com/docker/distribution/health/checks"
+	prometheus "github.com/docker/distribution/metrics"
 	"github.com/docker/distribution/notifications"
 	"github.com/docker/distribution/reference"
 	"github.com/docker/distribution/registry/api/errcode"
@@ -35,6 +36,7 @@ import (
 	"github.com/docker/distribution/registry/storage/driver/factory"
 	storagemiddleware "github.com/docker/distribution/registry/storage/driver/middleware"
 	"github.com/docker/distribution/version"
+	"github.com/docker/go-metrics"
 	"github.com/docker/libtrust"
 	"github.com/garyburd/redigo/redis"
 	"github.com/gorilla/mux"
@@ -412,6 +414,15 @@ func (app *App) RegisterHealthChecks(healthRegistries ...*health.Registry) {
 // passed through the application filters and context will be constructed at
 // request time.
 func (app *App) register(routeName string, dispatch dispatchFunc) {
+	handler := app.dispatcher(dispatch)
+
+	// Chain the handler with prometheus instrumented handler
+	if app.Config.HTTP.Debug.Prometheus.Enabled {
+		namespace := metrics.NewNamespace(prometheus.NamespacePrefix, "http", nil)
+		httpMetrics := namespace.NewDefaultHttpMetrics(strings.Replace(routeName, "-", "_", -1))
+		metrics.Register(namespace)
+		handler = metrics.InstrumentHandler(httpMetrics, handler)
+	}
 	// TODO(stevvooe): This odd dispatcher/route registration is by-product of
 	// some limitations in the gorilla/mux router. We are using it to keep
@@ -419,7 +430,7 @@ func (app *App) register(routeName string, dispatch dispatchFunc) {
 	// replace it with manual routing and structure-based dispatch for better
 	// control over the request execution.
-	app.router.GetRoute(routeName).Handler(app.dispatcher(dispatch))
+	app.router.GetRoute(routeName).Handler(handler)
 }
 // configureEvents prepares the event sink for action.

registry/registry.go

@@ -21,6 +21,7 @@ import (
 	"github.com/docker/distribution/registry/listener"
 	"github.com/docker/distribution/uuid"
 	"github.com/docker/distribution/version"
+	"github.com/docker/go-metrics"
 	gorhandlers "github.com/gorilla/handlers"
 	log "github.com/sirupsen/logrus"
 	"github.com/spf13/cobra"
@@ -58,6 +59,15 @@ var ServeCmd = &cobra.Command{
 			log.Fatalln(err)
 		}
+		if config.HTTP.Debug.Prometheus.Enabled {
+			path := config.HTTP.Debug.Prometheus.Path
+			if path == "" {
+				path = "/metrics"
+			}
+			log.Info("providing prometheus metrics on ", path)
+			http.Handle(path, metrics.Handler())
+		}
+
 		if err = registry.ListenAndServe(); err != nil {
 			log.Fatalln(err)
 		}

registry/storage/cache/cachedblobdescriptorstore.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"github.com/docker/distribution"
+	prometheus "github.com/docker/distribution/metrics"
 	"github.com/opencontainers/go-digest"
 )
@@ -38,6 +39,11 @@ type cachedBlobStatter struct {
 	tracker MetricsTracker
 }
+var (
+	// cacheCount is the number of total cache request received/hits/misses
+	cacheCount = prometheus.StorageNamespace.NewLabeledCounter("cache", "The number of cache request received", "type")
+)
+
 // NewCachedBlobStatter creates a new statter which prefers a cache and
 // falls back to a backend.
 func NewCachedBlobStatter(cache distribution.BlobDescriptorService, backend distribution.BlobDescriptorService) distribution.BlobDescriptorService {
@@ -58,6 +64,7 @@ func NewCachedBlobStatterWithMetrics(cache distribution.BlobDescriptorService, b
 }
 func (cbds *cachedBlobStatter) Stat(ctx context.Context, dgst digest.Digest) (distribution.Descriptor, error) {
+	cacheCount.WithValues("Request").Inc(1)
 	desc, err := cbds.cache.Stat(ctx, dgst)
 	if err != nil {
 		if err != distribution.ErrBlobUnknown {
@@ -66,12 +73,13 @@ func (cbds *cachedBlobStatter) Stat(ctx context.Context, dgst digest.Digest) (di
 		goto fallback
 	}
-
+	cacheCount.WithValues("Hit").Inc(1)
 	if cbds.tracker != nil {
 		cbds.tracker.Hit()
 	}
 	return desc, nil
 fallback:
+	cacheCount.WithValues("Miss").Inc(1)
 	if cbds.tracker != nil {
 		cbds.tracker.Miss()
 	}

registry/storage/driver/base/base.go

@@ -42,9 +42,21 @@ import (
 	"io"
 	dcontext "github.com/docker/distribution/context"
+	prometheus "github.com/docker/distribution/metrics"
 	storagedriver "github.com/docker/distribution/registry/storage/driver"
+	"github.com/docker/go-metrics"
+	"time"
 )
+var (
+	// storageAction is the metrics of blob related operations
+	storageAction = prometheus.StorageNamespace.NewLabeledTimer("action", "The number of seconds that the storage action takes", "driver", "action")
+)
+
+func init() {
+	metrics.Register(prometheus.StorageNamespace)
+}
+
 // Base provides a wrapper around a storagedriver implementation that provides
 // common path and bounds checking.
 type Base struct {
@@ -87,7 +99,9 @@ func (base *Base) GetContent(ctx context.Context, path string) ([]byte, error) {
 		return nil, storagedriver.InvalidPathError{Path: path, DriverName: base.StorageDriver.Name()}
 	}
+	start := time.Now()
 	b, e := base.StorageDriver.GetContent(ctx, path)
+	storageAction.WithValues(base.Name(), "GetContent").UpdateSince(start)
 	return b, base.setDriverName(e)
 }
@@ -100,7 +114,10 @@ func (base *Base) PutContent(ctx context.Context, path string, content []byte) e
 		return storagedriver.InvalidPathError{Path: path, DriverName: base.StorageDriver.Name()}
 	}
-	return base.setDriverName(base.StorageDriver.PutContent(ctx, path, content))
+	start := time.Now()
+	err := base.setDriverName(base.StorageDriver.PutContent(ctx, path, content))
+	storageAction.WithValues(base.Name(), "PutContent").UpdateSince(start)
+	return err
 }
 // Reader wraps Reader of underlying storage driver.
@@ -142,7 +159,9 @@ func (base *Base) Stat(ctx context.Context, path string) (storagedriver.FileInfo
 		return nil, storagedriver.InvalidPathError{Path: path, DriverName: base.StorageDriver.Name()}
 	}
+	start := time.Now()
 	fi, e := base.StorageDriver.Stat(ctx, path)
+	storageAction.WithValues(base.Name(), "Stat").UpdateSince(start)
 	return fi, base.setDriverName(e)
 }
@@ -155,7 +174,9 @@ func (base *Base) List(ctx context.Context, path string) ([]string, error) {
 		return nil, storagedriver.InvalidPathError{Path: path, DriverName: base.StorageDriver.Name()}
 	}
+	start := time.Now()
 	str, e := base.StorageDriver.List(ctx, path)
+	storageAction.WithValues(base.Name(), "List").UpdateSince(start)
 	return str, base.setDriverName(e)
 }
@@ -170,7 +191,10 @@ func (base *Base) Move(ctx context.Context, sourcePath string, destPath string)
 		return storagedriver.InvalidPathError{Path: destPath, DriverName: base.StorageDriver.Name()}
 	}
-	return base.setDriverName(base.StorageDriver.Move(ctx, sourcePath, destPath))
+	start := time.Now()
+	err := base.setDriverName(base.StorageDriver.Move(ctx, sourcePath, destPath))
+	storageAction.WithValues(base.Name(), "Move").UpdateSince(start)
+	return err
 }
 // Delete wraps Delete of underlying storage driver.
@@ -182,7 +206,10 @@ func (base *Base) Delete(ctx context.Context, path string) error {
 		return storagedriver.InvalidPathError{Path: path, DriverName: base.StorageDriver.Name()}
 	}
-	return base.setDriverName(base.StorageDriver.Delete(ctx, path))
+	start := time.Now()
+	err := base.setDriverName(base.StorageDriver.Delete(ctx, path))
+	storageAction.WithValues(base.Name(), "Delete").UpdateSince(start)
+	return err
 }
 // URLFor wraps URLFor of underlying storage driver.
@@ -194,7 +221,9 @@ func (base *Base) URLFor(ctx context.Context, path string, options map[string]in
 		return "", storagedriver.InvalidPathError{Path: path, DriverName: base.StorageDriver.Name()}
 	}
+	start := time.Now()
 	str, e := base.StorageDriver.URLFor(ctx, path, options)
+	storageAction.WithValues(base.Name(), "URLFor").UpdateSince(start)
 	return str, base.setDriverName(e)
 }

registry/storage/tagstore.go

@@ -122,17 +122,20 @@ func (ts *tagStore) Untag(ctx context.Context, tag string) error {
 		name: ts.repository.Named().Name(),
 		tag:  tag,
 	})
-
-	switch err.(type) {
-	case storagedriver.PathNotFoundError:
-		return distribution.ErrTagUnknown{Tag: tag}
-	case nil:
-		break
-	default:
+	if err != nil {
 		return err
 	}
-	return ts.blobStore.driver.Delete(ctx, tagPath)
+	if err := ts.blobStore.driver.Delete(ctx, tagPath); err != nil {
+		switch err.(type) {
+		case storagedriver.PathNotFoundError:
+			return nil // Untag is idempotent, we don't care if it didn't exist
+		default:
+			return err
+		}
+	}
+
+	return nil
 }
 // linkedBlobStore returns the linkedBlobStore for the named tag, allowing one
@@ -179,6 +182,10 @@ func (ts *tagStore) Lookup(ctx context.Context, desc distribution.Descriptor) ([
 		tagLinkPath, err := pathFor(tagLinkPathSpec)
 		tagDigest, err := ts.blobStore.readlink(ctx, tagLinkPath)
 		if err != nil {
+			switch err.(type) {
+			case storagedriver.PathNotFoundError:
+				continue
+			}
 			return nil, err
 		}

registry/storage/tagstore_test.go

@@ -84,8 +84,8 @@ func TestTagStoreUnTag(t *testing.T) {
 	desc := distribution.Descriptor{Digest: "sha256:bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb"}
 	err := tags.Untag(ctx, "latest")
-	if err == nil {
-		t.Errorf("Expected error untagging non-existant tag")
+	if err != nil {
+		t.Error(err)
 	}
 	err = tags.Tag(ctx, "latest", desc)

vendor.conf

@@ -3,11 +3,13 @@ github.com/Azure/go-autorest ec5f4903f77ed9927ac95b19ab8e44ada64c1356
 github.com/sirupsen/logrus 3d4380f53a34dcdc95f0c1db702615992b38d9a4
 github.com/aws/aws-sdk-go 5bcc0a238d880469f949fc7cd24e35f32ab80cbd
 github.com/bshuster-repo/logrus-logstash-hook d2c0ecc1836d91814e15e23bb5dc309c3ef51f4a
+github.com/beorn7/perks 4c0e84591b9aa9e6dcfdf3e020114cd81f89d5f9
 github.com/bugsnag/bugsnag-go b1d153021fcd90ca3f080db36bec96dc690fb274
 github.com/bugsnag/osext 0dd3f918b21bec95ace9dc86c7e70266cfc5c702
 github.com/bugsnag/panicwrap e2c28503fcd0675329da73bf48b33404db873782
 github.com/denverdino/aliyungo afedced274aa9a7fcdd47ac97018f0f8db4e5de2
 github.com/dgrijalva/jwt-go a601269ab70c205d26370c16f7c81e9017c14e04
+github.com/docker/go-metrics 399ea8c73916000c64c2c76e8da00ca82f8387ab
 github.com/docker/goamz f0a21f5b2e12f83a505ecf79b633bb2035cf6f85
 github.com/docker/libtrust fa567046d9b14f6aa788882a950d69651d230b21
 github.com/garyburd/redigo 535138d7bcd717d6531c701ef5933d98b1866257
@@ -18,9 +20,14 @@ github.com/gorilla/handlers 60c7bfde3e33c201519a200a4507a158cc03a17b
 github.com/gorilla/mux 599cba5e7b6137d46ddf58fb1765f5d928e69604
 github.com/inconshreveable/mousetrap 76626ae9c91c4f2a10f34cad8ce83ea42c93bb75
 github.com/jmespath/go-jmespath bd40a432e4c76585ef6b72d3fd96fb9b6dc7b68d
+github.com/matttproud/golang_protobuf_extensions c12348ce28de40eed0136aa2b644d0ee0650e56c
 github.com/miekg/dns 271c58e0c14f552178ea321a545ff9af38930f39
 github.com/mitchellh/mapstructure 482a9fd5fa83e8c4e7817413b80f3eb8feec03ef
 github.com/ncw/swift b964f2ca856aac39885e258ad25aec08d5f64ee6
+github.com/prometheus/client_golang c332b6f63c0658a65eca15c0e5247ded801cf564
+github.com/prometheus/client_model 99fa1f4be8e564e8a6b613da7fa6f46c9edafc6c
+github.com/prometheus/common 89604d197083d4781071d3c65855d24ecfb0a563
+github.com/prometheus/procfs cb4147076ac75738c9a7d279075a253c0cc5acbd
 github.com/spf13/cobra 312092086bed4968099259622145a0c9ae280064
 github.com/spf13/pflag 5644820622454e71517561946e3d94b9f9db6842
 github.com/stevvooe/resumable 2aaf90b2ceea5072cb503ef2a620b08ff3119870
@@ -40,4 +47,4 @@ gopkg.in/check.v1 64131543e7896d5bcc6bd5a76287eb75ea96c673
 gopkg.in/square/go-jose.v1 40d457b439244b546f023d056628e5184136899b
 gopkg.in/yaml.v2 bef53efd0c76e49e6de55ead051f886bea7e9420
 rsc.io/letsencrypt e770c10b0f1a64775ae91d240407ce00d1a5bdeb https://github.com/dmcgowan/letsencrypt.git
-github.com/opencontainers/go-digest a6d0ee40d4207ea02364bd3b9e8e77b9159ba1eb
+github.com/opencontainers/go-digest a6d0ee40d4207ea02364bd3b9e8e77b9159ba1eb
\ No newline at end of file

vendor/github.com/beorn7/perks/LICENSE

+Copyright (C) 2013 Blake Mizerany
+
+Permission is hereby granted, free of charge, to any person obtaining
+a copy of this software and associated documentation files (the
+"Software"), to deal in the Software without restriction, including
+without limitation the rights to use, copy, modify, merge, publish,
+distribute, sublicense, and/or sell copies of the Software, and to
+permit persons to whom the Software is furnished to do so, subject to
+the following conditions:
+
+The above copyright notice and this permission notice shall be
+included in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

vendor/github.com/beorn7/perks/README.md

+# Perks for Go (golang.org)
+
+Perks contains the Go package quantile that computes approximate quantiles over
+an unbounded data stream within low memory and CPU bounds.
+
+For more information and examples, see:
+http://godoc.org/github.com/bmizerany/perks
+
+A very special thank you and shout out to Graham Cormode (Rutgers University),
+Flip Korn (AT&T Labs–Research), S. Muthukrishnan (Rutgers University), and
+Divesh Srivastava (AT&T Labs–Research) for their research and publication of
+[Effective Computation of Biased Quantiles over Data Streams](http://www.cs.rutgers.edu/~muthu/bquant.pdf)
+
+Thank you, also:
+* Armon Dadgar (@armon)
+* Andrew Gerrand (@nf)
+* Brad Fitzpatrick (@bradfitz)
+* Keith Rarick (@kr)
+
+FAQ:
+
+Q: Why not move the quantile package into the project root?
+A: I want to add more packages to perks later.
+
+Copyright (C) 2013 Blake Mizerany
+
+Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

vendor/github.com/beorn7/perks/quantile/stream.go

+// Package quantile computes approximate quantiles over an unbounded data
+// stream within low memory and CPU bounds.
+//
+// A small amount of accuracy is traded to achieve the above properties.
+//
+// Multiple streams can be merged before calling Query to generate a single set
+// of results. This is meaningful when the streams represent the same type of
+// data. See Merge and Samples.
+//
+// For more detailed information about the algorithm used, see:
+//
+// Effective Computation of Biased Quantiles over Data Streams
+//
+// http://www.cs.rutgers.edu/~muthu/bquant.pdf
+package quantile
+
+import (
+	"math"
+	"sort"
+)
+
+// Sample holds an observed value and meta information for compression. JSON
+// tags have been added for convenience.
+type Sample struct {
+	Value float64 `json:",string"`
+	Width float64 `json:",string"`
+	Delta float64 `json:",string"`
+}
+
+// Samples represents a slice of samples. It implements sort.Interface.
+type Samples []Sample
+
+func (a Samples) Len() int           { return len(a) }
+func (a Samples) Less(i, j int) bool { return a[i].Value < a[j].Value }
+func (a Samples) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }
+
+type invariant func(s *stream, r float64) float64
+
+// NewLowBiased returns an initialized Stream for low-biased quantiles
+// (e.g. 0.01, 0.1, 0.5) where the needed quantiles are not known a priori, but
+// error guarantees can still be given even for the lower ranks of the data
+// distribution.
+//
+// The provided epsilon is a relative error, i.e. the true quantile of a value
+// returned by a query is guaranteed to be within (1±Epsilon)*Quantile.
+//
+// See http://www.cs.rutgers.edu/~muthu/bquant.pdf for time, space, and error
+// properties.
+func NewLowBiased(epsilon float64) *Stream {
+	ƒ := func(s *stream, r float64) float64 {
+		return 2 * epsilon * r
+	}
+	return newStream(ƒ)
+}
+
+// NewHighBiased returns an initialized Stream for high-biased quantiles
+// (e.g. 0.01, 0.1, 0.5) where the needed quantiles are not known a priori, but
+// error guarantees can still be given even for the higher ranks of the data
+// distribution.
+//
+// The provided epsilon is a relative error, i.e. the true quantile of a value
+// returned by a query is guaranteed to be within 1-(1±Epsilon)*(1-Quantile).
+//
+// See http://www.cs.rutgers.edu/~muthu/bquant.pdf for time, space, and error
+// properties.
+func NewHighBiased(epsilon float64) *Stream {
+	ƒ := func(s *stream, r float64) float64 {
+		return 2 * epsilon * (s.n - r)
+	}
+	return newStream(ƒ)
+}
+
+// NewTargeted returns an initialized Stream concerned with a particular set of
+// quantile values that are supplied a priori. Knowing these a priori reduces
+// space and computation time. The targets map maps the desired quantiles to
+// their absolute errors, i.e. the true quantile of a value returned by a query
+// is guaranteed to be within (Quantile±Epsilon).
+//
+// See http://www.cs.rutgers.edu/~muthu/bquant.pdf for time, space, and error properties.
+func NewTargeted(targets map[float64]float64) *Stream {
+	ƒ := func(s *stream, r float64) float64 {
+		var m = math.MaxFloat64
+		var f float64
+		for quantile, epsilon := range targets {
+			if quantile*s.n <= r {
+				f = (2 * epsilon * r) / quantile
+			} else {
+				f = (2 * epsilon * (s.n - r)) / (1 - quantile)
+			}
+			if f < m {
+				m = f
+			}
+		}
+		return m
+	}
+	return newStream(ƒ)
+}
+
+// Stream computes quantiles for a stream of float64s. It is not thread-safe by
+// design. Take care when using across multiple goroutines.
+type Stream struct {
+	*stream
+	b      Samples
+	sorted bool
+}
+
+func newStream(ƒ invariant) *Stream {
+	x := &stream{ƒ: ƒ}
+	return &Stream{x, make(Samples, 0, 500), true}
+}
+
+// Insert inserts v into the stream.
+func (s *Stream) Insert(v float64) {
+	s.insert(Sample{Value: v, Width: 1})
+}
+
+func (s *Stream) insert(sample Sample) {
+	s.b = append(s.b, sample)
+	s.sorted = false
+	if len(s.b) == cap(s.b) {
+		s.flush()
+	}
+}
+
+// Query returns the computed qth percentiles value. If s was created with
+// NewTargeted, and q is not in the set of quantiles provided a priori, Query
+// will return an unspecified result.
+func (s *Stream) Query(q float64) float64 {
+	if !s.flushed() {
+		// Fast path when there hasn't been enough data for a flush;
+		// this also yields better accuracy for small sets of data.
+		l := len(s.b)
+		if l == 0 {
+			return 0
+		}
+		i := int(math.Ceil(float64(l) * q))
+		if i > 0 {
+			i -= 1
+		}
+		s.maybeSort()
+		return s.b[i].Value
+	}
+	s.flush()
+	return s.stream.query(q)
+}
+
+// Merge merges samples into the underlying streams samples. This is handy when
+// merging multiple streams from separate threads, database shards, etc.
+//
+// ATTENTION: This method is broken and does not yield correct results. The
+// underlying algorithm is not capable of merging streams correctly.
+func (s *Stream) Merge(samples Samples) {
+	sort.Sort(samples)
+	s.stream.merge(samples)
+}
+
+// Reset reinitializes and clears the list reusing the samples buffer memory.
+func (s *Stream) Reset() {
+	s.stream.reset()
+	s.b = s.b[:0]
+}
+
+// Samples returns stream samples held by s.
+func (s *Stream) Samples() Samples {
+	if !s.flushed() {
+		return s.b
+	}
+	s.flush()
+	return s.stream.samples()
+}
+
+// Count returns the total number of samples observed in the stream
+// since initialization.
+func (s *Stream) Count() int {
+	return len(s.b) + s.stream.count()
+}
+
+func (s *Stream) flush() {
+	s.maybeSort()
+	s.stream.merge(s.b)
+	s.b = s.b[:0]
+}
+
+func (s *Stream) maybeSort() {
+	if !s.sorted {
+		s.sorted = true
+		sort.Sort(s.b)
+	}
+}
+
+func (s *Stream) flushed() bool {
+	return len(s.stream.l) > 0
+}
+
+type stream struct {
+	n float64
+	l []Sample
+	ƒ invariant
+}
+
+func (s *stream) reset() {
+	s.l = s.l[:0]
+	s.n = 0
+}
+
+func (s *stream) insert(v float64) {
+	s.merge(Samples{{v, 1, 0}})
+}
+
+func (s *stream) merge(samples Samples) {
+	// TODO(beorn7): This tries to merge not only individual samples, but
+	// whole summaries. The paper doesn't mention merging summaries at
+	// all. Unittests show that the merging is inaccurate. Find out how to
+	// do merges properly.
+	var r float64
+	i := 0
+	for _, sample := range samples {
+		for ; i < len(s.l); i++ {
+			c := s.l[i]
+			if c.Value > sample.Value {
+				// Insert at position i.
+				s.l = append(s.l, Sample{})
+				copy(s.l[i+1:], s.l[i:])
+				s.l[i] = Sample{
+					sample.Value,
+					sample.Width,
+					math.Max(sample.Delta, math.Floor(s.ƒ(s, r))-1),
+					// TODO(beorn7): How to calculate delta correctly?
+				}
+				i++
+				goto inserted
+			}
+			r += c.Width
+		}
+		s.l = append(s.l, Sample{sample.Value, sample.Width, 0})
+		i++
+	inserted:
+		s.n += sample.Width
+		r += sample.Width
+	}
+	s.compress()
+}
+
+func (s *stream) count() int {
+	return int(s.n)
+}
+
+func (s *stream) query(q float64) float64 {
+	t := math.Ceil(q * s.n)
+	t += math.Ceil(s.ƒ(s, t) / 2)
+	p := s.l[0]
+	var r float64
+	for _, c := range s.l[1:] {
+		r += p.Width
+		if r+c.Width+c.Delta > t {
+			return p.Value
+		}
+		p = c
+	}
+	return p.Value
+}
+
+func (s *stream) compress() {
+	if len(s.l) < 2 {
+		return
+	}
+	x := s.l[len(s.l)-1]
+	xi := len(s.l) - 1
+	r := s.n - 1 - x.Width
+
+	for i := len(s.l) - 2; i >= 0; i-- {
+		c := s.l[i]
+		if c.Width+x.Width+x.Delta <= s.ƒ(s, r) {
+			x.Width += c.Width
+			s.l[xi] = x
+			// Remove element at i.
+			copy(s.l[i:], s.l[i+1:])
+			s.l = s.l[:len(s.l)-1]
+			xi -= 1
+		} else {
+			x = c
+			xi = i
+		}
+		r -= c.Width
+	}
+}
+
+func (s *stream) samples() Samples {
+	samples := make(Samples, len(s.l))
+	copy(samples, s.l)
+	return samples
+}

vendor/github.com/docker/go-metrics/LICENSE.code

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vendor/github.com/docker/go-metrics/LICENSE.docs

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+Section 6 -- Term and Termination.
+
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+          it is cured within 30 days of Your discovery of the
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+
+     For the avoidance of doubt, this Section 6(b) does not affect any
+     right the Licensor may have to seek remedies for Your violations
+     of this Public License.
+
+  c. For the avoidance of doubt, the Licensor may also offer the
+     Licensed Material under separate terms or conditions or stop
+     distributing the Licensed Material at any time; however, doing so
+     will not terminate this Public License.
+
+  d. Sections 1, 5, 6, 7, and 8 survive termination of this Public
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+
+  b. Any arrangements, understandings, or agreements regarding the
+     Licensed Material not stated herein are separate from and
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+
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+Section 8 -- Interpretation.
+
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+     conditions on any use of the Licensed Material that could lawfully
+     be made without permission under this Public License.
+
+  b. To the extent possible, if any provision of this Public License is
+     deemed unenforceable, it shall be automatically reformed to the
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+
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+     failure to comply consented to unless expressly agreed to by the
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+=======================================================================
+
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+licenses to material it publishes and in those instances will be
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vendor/github.com/docker/go-metrics/NOTICE

+Docker
+Copyright 2012-2015 Docker, Inc.
+
+This product includes software developed at Docker, Inc. (https://www.docker.com).
+
+The following is courtesy of our legal counsel:
+
+
+Use and transfer of Docker may be subject to certain restrictions by the
+United States and other governments.
+It is your responsibility to ensure that your use and/or transfer does not
+violate applicable laws.
+
+For more information, please see https://www.bis.doc.gov
+
+See also https://www.apache.org/dev/crypto.html and/or seek legal counsel.

vendor/github.com/docker/go-metrics/README.md

+# go-metrics [![GoDoc](https://godoc.org/github.com/docker/go-metrics?status.svg)](https://godoc.org/github.com/docker/go-metrics) ![Badge Badge](http://doyouevenbadge.com/github.com/docker/go-metrics)
+
+This package is small wrapper around the prometheus go client to help enforce convention and best practices for metrics collection in Docker projects.
+
+## Best Practices
+
+This packages is meant to be used for collecting metrics in Docker projects.
+It is not meant to be used as a replacement for the prometheus client but to help enforce consistent naming across metrics collected.
+If you have not already read the prometheus best practices around naming and labels you can read the page [here](https://prometheus.io/docs/practices/naming/).
+
+The following are a few Docker specific rules that will help you name and work with metrics in your project.
+
+1. Namespace and Subsystem
+
+This package provides you with a namespace type that allows you to specify the same namespace and subsystem for your metrics.
+
+```go
+ns := metrics.NewNamespace("engine", "daemon", metrics.Labels{
+        "version": dockerversion.Version,
+        "commit":  dockerversion.GitCommit,
+})
+```
+
+In the example above we are creating metrics for the Docker engine's daemon package.
+`engine` would be the namespace in this example where `daemon` is the subsystem or package where we are collecting the metrics.
+
+A namespace also allows you to attach constant labels to the metrics such as the git commit and version that it is collecting.
+
+2. Declaring your Metrics
+
+Try to keep all your metric declarations in one file.
+This makes it easy for others to see what constant labels are defined on the namespace and what labels are defined on the metrics when they are created.
+
+3. Use labels instead of multiple metrics
+
+Labels allow you to define one metric such as the time it takes to perform a certain action on an object.
+If we wanted to collect timings on various container actions such as create, start, and delete then we can define one metric called `container_actions` and use labels to specify the type of action.
+
+
+```go
+containerActions = ns.NewLabeledTimer("container_actions", "The number of milliseconds it takes to process each container action", "action")
+```
+
+The last parameter is the label name or key.
+When adding a data point to the metric you will use the `WithValues` function to specify the `action` that you are collecting for.
+
+```go
+containerActions.WithValues("create").UpdateSince(start)
+```
+
+4. Always use a unit
+
+The metric name should describe what you are measuring but you also need to provide the unit that it is being measured with.
+For a timer, the standard unit is seconds and a counter's standard unit is a total.
+For gauges you must provide the unit.
+This package provides a standard set of units for use within the Docker projects.
+
+```go
+Nanoseconds Unit = "nanoseconds"
+Seconds     Unit = "seconds"
+Bytes       Unit = "bytes"
+Total       Unit = "total"
+```
+
+If you need to use a unit but it is not defined in the package please open a PR to add it but first try to see if one of the already created units will work for your metric, i.e. seconds or nanoseconds vs adding milliseconds.
+
+## Docs
+
+Package documentation can be found [here](https://godoc.org/github.com/docker/go-metrics).
+
+## HTTP Metrics
+
+To instrument a http handler, you can wrap the code like this:
+
+```go
+namespace := metrics.NewNamespace("docker_distribution", "http", metrics.Labels{"handler": "your_http_handler_name"})
+httpMetrics := namespace.NewDefaultHttpMetrics()
+metrics.Register(namespace)
+instrumentedHandler = metrics.InstrumentHandler(httpMetrics, unInstrumentedHandler)
+```
+Note: The `handler` label must be provided when a new namespace is created.
+
+## Additional Metrics
+
+Additional metrics are also defined here that are not available in the prometheus client.
+If you need a custom metrics and it is generic enough to be used by multiple projects, define it here.
+
+
+## Copyright and license
+
+Copyright © 2016 Docker, Inc. All rights reserved, except as follows. Code is released under the Apache 2.0 license. The README.md file, and files in the "docs" folder are licensed under the Creative Commons Attribution 4.0 International License under the terms and conditions set forth in the file "LICENSE.docs". You may obtain a duplicate copy of the same license, titled CC-BY-SA-4.0, at http://creativecommons.org/licenses/by/4.0/.

vendor/github.com/docker/go-metrics/counter.go

+package metrics
+
+import "github.com/prometheus/client_golang/prometheus"
+
+// Counter is a metrics that can only increment its current count
+type Counter interface {
+	// Inc adds Sum(vs) to the counter. Sum(vs) must be positive.
+	//
+	// If len(vs) == 0, increments the counter by 1.
+	Inc(vs ...float64)
+}
+
+// LabeledCounter is counter that must have labels populated before use.
+type LabeledCounter interface {
+	WithValues(vs ...string) Counter
+}
+
+type labeledCounter struct {
+	pc *prometheus.CounterVec
+}
+
+func (lc *labeledCounter) WithValues(vs ...string) Counter {
+	return &counter{pc: lc.pc.WithLabelValues(vs...)}
+}
+
+func (lc *labeledCounter) Describe(ch chan<- *prometheus.Desc) {
+	lc.pc.Describe(ch)
+}
+
+func (lc *labeledCounter) Collect(ch chan<- prometheus.Metric) {
+	lc.pc.Collect(ch)
+}
+
+type counter struct {
+	pc prometheus.Counter
+}
+
+func (c *counter) Inc(vs ...float64) {
+	if len(vs) == 0 {
+		c.pc.Inc()
+	}
+
+	c.pc.Add(sumFloat64(vs...))
+}
+
+func (c *counter) Describe(ch chan<- *prometheus.Desc) {
+	c.pc.Describe(ch)
+}
+
+func (c *counter) Collect(ch chan<- prometheus.Metric) {
+	c.pc.Collect(ch)
+}