Implements a credentialprovider library for use by DockerPuller.

This change refactors the way Kubelet's DockerPuller handles the docker config credentials to utilize a new credentialprovider library.

The credentialprovider library is based on several of the files from the Kubelet's dockertools directory, but supports a new pluggable model for retrieving a .dockercfg-compatible JSON blob with credentials.

With this change, the Kubelet will lazily ask for the docker config from a set of DockerConfigProvider extensions each time it needs a credential.

This change provides common implementations of DockerConfigProvider for:
 - "Default": load .dockercfg from disk
 - "Caching": wraps another provider in a cache that expires after a pre-specified lifetime.

GCP-only:
 - "google-dockercfg": reads a .dockercfg from a GCE instance's metadata
 - "google-dockercfg-url": reads a .dockercfg from a URL specified in a GCE instance's metadata.
 - "google-container-registry": reads an access token from GCE metadata into a password field.

cluster/gce/config-default.sh

@@ -31,7 +31,7 @@ MASTER_TAG="${INSTANCE_PREFIX}-master"
 MINION_TAG="${INSTANCE_PREFIX}-minion"
 MINION_NAMES=($(eval echo ${INSTANCE_PREFIX}-minion-{1..${NUM_MINIONS}}))
 MINION_IP_RANGES=($(eval echo "10.244.{1..${NUM_MINIONS}}.0/24"))
-MINION_SCOPES="compute-rw"
+MINION_SCOPES="storage-ro,compute-rw"
 # Increase the sleep interval value if concerned about API rate limits. 3, in seconds, is the default.
 POLL_SLEEP_INTERVAL=3
 PORTAL_NET="10.0.0.0/16"

cmd/kubelet/plugins.go

@@ -0,0 +1,24 @@
+/*
+Copyright 2014 Google Inc. All rights reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package main
+
+// This file exists to force the desired plugin implementations to be linked.
+// This should probably be part of some configuration fed into the build for a
+// given binary target.
+import (
+	_ "github.com/GoogleCloudPlatform/kubernetes/pkg/credentialprovider/gcp"
+)

hack/e2e-suite/private.sh

@@ -0,0 +1,86 @@
+#!/bin/bash
+
+# Copyright 2014 Google Inc. All rights reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# Launches a container and verifies it can be reached. Assumes that
+# we're being called by hack/e2e-test.sh (we use some env vars it sets up).
+
+set -o errexit
+set -o nounset
+set -o pipefail
+
+if [[ "${KUBERNETES_PROVIDER:-gce}" != "gce" ]]; then
+  echo WARNING: Skipping private.sh for cloud provider: $KUBERNETES_PROVIDER.
+  exit 0
+fi
+
+KUBE_ROOT=$(dirname "${BASH_SOURCE}")/../..
+source "${KUBE_ROOT}/cluster/kube-env.sh"
+source "${KUBE_ROOT}/cluster/$KUBERNETES_PROVIDER/util.sh"
+
+# Launch some pods.
+num_pods=2
+$KUBECFG -p 8080:9376 run container.cloud.google.com/_b_k8s_test/serve_hostname ${num_pods} my-hostname
+
+function teardown() {
+  echo "Cleaning up test artifacts"
+  $KUBECFG stop my-hostname
+  $KUBECFG rm my-hostname
+}
+
+trap "teardown" EXIT
+
+pod_id_list=$($KUBECFG '-template={{range.items}}{{.id}} {{end}}' -l replicationController=my-hostname list pods)
+# Pod turn up on a clean cluster can take a while for the docker image pull.
+all_running=0
+for i in $(seq 1 24); do
+  echo "Waiting for pods to come up."
+  sleep 5
+  all_running=1
+  for id in $pod_id_list; do
+    current_status=$($KUBECFG -template '{{.currentState.status}}' get pods/$id) || true
+    if [[ "$current_status" != "Running" ]]; then
+      all_running=0
+      break
+    fi
+  done
+  if [[ "${all_running}" == 1 ]]; then
+    break
+  fi
+done
+if [[ "${all_running}" == 0 ]]; then
+  echo "Pods did not come up in time"
+  exit 1
+fi
+
+# Get minion IP addresses
+detect-minions
+
+# let images stabilize
+echo "Letting images stabilize"
+sleep 5
+
+# Verify that something is listening.
+for id in ${pod_id_list}; do
+  ip=$($KUBECFG -template '{{.currentState.hostIP}}' get pods/$id)
+  echo "Trying to reach server that should be running at ${ip}:8080..."
+  ok=0
+  for i in $(seq 1 5); do
+    curl --connect-timeout 1 "http://${ip}:8080" >/dev/null 2>&1 && ok=1 && break
+    sleep 2
+  done
+done
+
+exit 0

pkg/credentialprovider/config.go

@@ -14,26 +14,38 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-package dockertools
+package credentialprovider
 
 import (
 	"encoding/base64"
 	"encoding/json"
 	"fmt"
 	"io/ioutil"
-	"net/url"
+	"net/http"
 	"path/filepath"
 	"strings"
 
-	"github.com/fsouza/go-dockerclient"
 	"github.com/golang/glog"
 )
 
+// DockerConfig represents the config file used by the docker CLI.
+// This config that represents the credentials that should be used
+// when pulling images from specific image repositories.
+type DockerConfig map[string]DockerConfigEntry
+
+type DockerConfigEntry struct {
+	Username string
+	Password string
+	Email    string
+}
+
 const (
 	dockerConfigFileLocation = ".dockercfg"
 )
 
-func readDockerConfigFile() (cfg dockerConfig, err error) {
+func ReadDockerConfigFile() (cfg DockerConfig, err error) {
+	// TODO(mattmoor): This causes the Kubelet to read /.dockercfg,
+	// which is incorrect.  It should come from $HOME/.dockercfg.
 	absDockerConfigFileLocation, err := filepath.Abs(dockerConfigFileLocation)
 	if err != nil {
 		glog.Errorf("while trying to canonicalize %s: %v", dockerConfigFileLocation, err)
@@ -45,42 +57,58 @@ func readDockerConfigFile() (cfg dockerConfig, err error) {
 		glog.Errorf("while trying to read %s: %v", absDockerConfigFileLocation, err)
 		return nil, err
 	}
+
+	return readDockerConfigFileFromBytes(contents)
+}
+
+func ReadUrl(url string, client *http.Client, header *http.Header) (body []byte, err error) {
+	req, err := http.NewRequest("GET", url, nil)
+	if err != nil {
+		glog.Errorf("while creating request to read %s: %v", url, err)
+		return nil, err
+	}
+	if header != nil {
+		req.Header = *header
+	}
+	resp, err := client.Do(req)
+	if err != nil {
+		glog.Errorf("while trying to read %s: %v", url, err)
+		return nil, err
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != http.StatusOK {
+		err := fmt.Errorf("http status code: %d while fetching url: %v", resp.StatusCode)
+		glog.Errorf("while trying to read %s: %v", url, err)
+		glog.V(2).Infof("body of failing http response: %v", resp.Body)
+		return nil, err
+	}
+
+	contents, err := ioutil.ReadAll(resp.Body)
+	if err != nil {
+		glog.Errorf("while trying to read %s: %v", url, err)
+		return nil, err
+	}
+
+	return contents, nil
+}
+
+func ReadDockerConfigFileFromUrl(url string, client *http.Client, header *http.Header) (cfg DockerConfig, err error) {
+	if contents, err := ReadUrl(url, client, header); err != nil {
+		return nil, err
+	} else {
+		return readDockerConfigFileFromBytes(contents)
+	}
+}
+
+func readDockerConfigFileFromBytes(contents []byte) (cfg DockerConfig, err error) {
 	if err = json.Unmarshal(contents, &cfg); err != nil {
-		glog.Errorf("while trying to parse %s: %v", absDockerConfigFileLocation, err)
+		glog.Errorf("while trying to parse blob %q: %v", contents, err)
 		return nil, err
 	}
 	return
 }
 
-// dockerConfig represents the config file used by the docker CLI.
-// This config that represents the credentials that should be used
-// when pulling images from specific image repositories.
-type dockerConfig map[string]dockerConfigEntry
-
-func (dc dockerConfig) addToKeyring(dk *dockerKeyring) {
-	for loc, ident := range dc {
-		creds := docker.AuthConfiguration{
-			Username: ident.Username,
-			Password: ident.Password,
-			Email:    ident.Email,
-		}
-
-		parsed, err := url.Parse(loc)
-		if err != nil {
-			glog.Errorf("Entry %q in dockercfg invalid (%v), ignoring", loc, err)
-			continue
-		}
-
-		dk.add(parsed.Host+parsed.Path, creds)
-	}
-}
-
-type dockerConfigEntry struct {
-	Username string
-	Password string
-	Email    string
-}
-
 // dockerConfigEntryWithAuth is used solely for deserializing the Auth field
 // into a dockerConfigEntry during JSON deserialization.
 type dockerConfigEntryWithAuth struct {
@@ -90,7 +118,7 @@ type dockerConfigEntryWithAuth struct {
 	Auth     string
 }
 
-func (ident *dockerConfigEntry) UnmarshalJSON(data []byte) error {
+func (ident *DockerConfigEntry) UnmarshalJSON(data []byte) error {
 	var tmp dockerConfigEntryWithAuth
 	err := json.Unmarshal(data, &tmp)
 	if err != nil {

pkg/credentialprovider/config_test.go

@@ -14,20 +14,18 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-package dockertools
+package credentialprovider
 
 import (
 	"encoding/json"
 	"reflect"
 	"testing"
-
-	"github.com/fsouza/go-dockerclient"
 )
 
 func TestDockerConfigJSONDecode(t *testing.T) {
 	input := []byte(`{"http://foo.example.com":{"username": "foo", "password": "bar", "email": "foo@example.com"}, "http://bar.example.com":{"username": "bar", "password": "baz", "email": "bar@example.com"}}`)
 
-	expect := dockerConfig(map[string]dockerConfigEntry{
+	expect := DockerConfig(map[string]DockerConfigEntry{
 		"http://foo.example.com": {
 			Username: "foo",
 			Password: "bar",
@@ -40,7 +38,7 @@ func TestDockerConfigJSONDecode(t *testing.T) {
 		},
 	})
 
-	var output dockerConfig
+	var output DockerConfig
 	err := json.Unmarshal(input, &output)
 	if err != nil {
 		t.Errorf("Received unexpected error: %v", err)
@@ -54,13 +52,13 @@ func TestDockerConfigJSONDecode(t *testing.T) {
 func TestDockerConfigEntryJSONDecode(t *testing.T) {
 	tests := []struct {
 		input  []byte
-		expect dockerConfigEntry
+		expect DockerConfigEntry
 		fail   bool
 	}{
 		// simple case, just decode the fields
 		{
 			input: []byte(`{"username": "foo", "password": "bar", "email": "foo@example.com"}`),
-			expect: dockerConfigEntry{
+			expect: DockerConfigEntry{
 				Username: "foo",
 				Password: "bar",
 				Email:    "foo@example.com",
@@ -71,7 +69,7 @@ func TestDockerConfigEntryJSONDecode(t *testing.T) {
 		// auth field decodes to username & password
 		{
 			input: []byte(`{"auth": "Zm9vOmJhcg==", "email": "foo@example.com"}`),
-			expect: dockerConfigEntry{
+			expect: DockerConfigEntry{
 				Username: "foo",
 				Password: "bar",
 				Email:    "foo@example.com",
@@ -82,7 +80,7 @@ func TestDockerConfigEntryJSONDecode(t *testing.T) {
 		// auth field overrides username & password
 		{
 			input: []byte(`{"username": "foo", "password": "bar", "auth": "cGluZzpwb25n", "email": "foo@example.com"}`),
-			expect: dockerConfigEntry{
+			expect: DockerConfigEntry{
 				Username: "ping",
 				Password: "pong",
 				Email:    "foo@example.com",
@@ -93,7 +91,7 @@ func TestDockerConfigEntryJSONDecode(t *testing.T) {
 		// poorly-formatted auth causes failure
 		{
 			input: []byte(`{"auth": "pants", "email": "foo@example.com"}`),
-			expect: dockerConfigEntry{
+			expect: DockerConfigEntry{
 				Username: "",
 				Password: "",
 				Email:    "foo@example.com",
@@ -104,7 +102,7 @@ func TestDockerConfigEntryJSONDecode(t *testing.T) {
 		// invalid JSON causes failure
 		{
 			input: []byte(`{"email": false}`),
-			expect: dockerConfigEntry{
+			expect: DockerConfigEntry{
 				Username: "",
 				Password: "",
 				Email:    "",
@@ -114,7 +112,7 @@ func TestDockerConfigEntryJSONDecode(t *testing.T) {
 	}
 
 	for i, tt := range tests {
-		var output dockerConfigEntry
+		var output DockerConfigEntry
 		err := json.Unmarshal(tt.input, &output)
 		if (err != nil) != tt.fail {
 			t.Errorf("case %d: expected fail=%t, got err=%v", i, tt.fail, err)
@@ -168,41 +166,3 @@ func TestDecodeDockerConfigFieldAuth(t *testing.T) {
 		}
 	}
 }
-
-func TestDockerKeyringFromConfig(t *testing.T) {
-	cfg := dockerConfig(map[string]dockerConfigEntry{
-		"http://foo.example.com": {
-			Username: "foo",
-			Password: "bar",
-			Email:    "foo@example.com",
-		},
-		"https://bar.example.com": {
-			Username: "bar",
-			Password: "baz",
-			Email:    "bar@example.com",
-		},
-	})
-
-	dk := newDockerKeyring()
-	cfg.addToKeyring(dk)
-
-	expect := newDockerKeyring()
-	expect.add("foo.example.com",
-		docker.AuthConfiguration{
-			Username: "foo",
-			Password: "bar",
-			Email:    "foo@example.com",
-		},
-	)
-	expect.add("bar.example.com",
-		docker.AuthConfiguration{
-			Username: "bar",
-			Password: "baz",
-			Email:    "bar@example.com",
-		},
-	)
-
-	if !reflect.DeepEqual(expect, dk) {
-		t.Errorf("Received unexpected output. Expected %#v, got %#v", expect, dk)
-	}
-}

pkg/credentialprovider/doc.go

@@ -0,0 +1,19 @@
+/*
+Copyright 2014 Google Inc. All rights reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+// Package credentialprovider supplies interfaces and implementations for
+// docker registry providers to expose their authentication scheme.
+package credentialprovider

pkg/credentialprovider/gcp/doc.go

@@ -0,0 +1,19 @@
+/*
+Copyright 2014 Google Inc. All rights reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+// Package gcp_credentials contains  implementations of DockerConfigProvider
+// for Google Cloud Platform.
+package gcp_credentials

pkg/credentialprovider/gcp/metadata.go

@@ -0,0 +1,190 @@
+/*
+Copyright 2014 Google Inc. All rights reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package gcp_credentials
+
+import (
+	"encoding/json"
+	"net/http"
+	"strings"
+	"time"
+
+	"github.com/GoogleCloudPlatform/kubernetes/pkg/credentialprovider"
+	"github.com/golang/glog"
+)
+
+const (
+	metadataUrl        = "http://metadata.google.internal./computeMetadata/v1/"
+	metadataAttributes = metadataUrl + "instance/attributes/"
+	dockerConfigKey    = metadataAttributes + "google-dockercfg"
+	dockerConfigUrlKey = metadataAttributes + "google-dockercfg-url"
+	metadataScopes     = metadataUrl + "instance/service-accounts/default/scopes"
+	metadataToken      = metadataUrl + "instance/service-accounts/default/token"
+	metadataEmail      = metadataUrl + "instance/service-accounts/default/email"
+	storageScopePrefix = "https://www.googleapis.com/auth/devstorage"
+)
+
+var containerRegistryUrls = []string{"container.cloud.google.com"}
+
+var metadataHeader = &http.Header{
+	"Metadata-Flavor": []string{"Google"},
+}
+
+// A DockerConfigProvider that reads its configuration from Google
+// Compute Engine metadata.
+type metadataProvider struct {
+	Client *http.Client
+}
+
+// A DockerConfigProvider that reads its configuration from a specific
+// Google Compute Engine metadata key: 'google-dockercfg'.
+type dockerConfigKeyProvider struct {
+	metadataProvider
+}
+
+// A DockerConfigProvider that reads its configuration from a URL read from
+// a specific Google Compute Engine metadata key: 'google-dockercfg-url'.
+type dockerConfigUrlKeyProvider struct {
+	metadataProvider
+}
+
+// A DockerConfigProvider that provides a dockercfg with:
+//    Username: "_token"
+//    Password: "{access token from metadata}"
+type containerRegistryProvider struct {
+	metadataProvider
+}
+
+// init registers the various means by which credentials may
+// be resolved on GCP.
+func init() {
+	credentialprovider.RegisterCredentialProvider("google-dockercfg",
+		&credentialprovider.CachingDockerConfigProvider{
+			Provider: &dockerConfigKeyProvider{
+				metadataProvider{Client: http.DefaultClient},
+			},
+			Lifetime: 60 * time.Second,
+		})
+
+	credentialprovider.RegisterCredentialProvider("google-dockercfg-url",
+		&credentialprovider.CachingDockerConfigProvider{
+			Provider: &dockerConfigUrlKeyProvider{
+				metadataProvider{Client: http.DefaultClient},
+			},
+			Lifetime: 60 * time.Second,
+		})
+
+	credentialprovider.RegisterCredentialProvider("google-container-registry",
+		// Never cache this.  The access token is already
+		// cached by the metadata service.
+		&containerRegistryProvider{
+			metadataProvider{Client: http.DefaultClient},
+		})
+}
+
+// Enabled implements DockerConfigProvider for all of the Google implementations.
+func (g *metadataProvider) Enabled() bool {
+	_, err := credentialprovider.ReadUrl(metadataUrl, g.Client, metadataHeader)
+	return err == nil
+}
+
+// Provide implements DockerConfigProvider
+func (g *dockerConfigKeyProvider) Provide() credentialprovider.DockerConfig {
+	// Read the contents of the google-dockercfg metadata key and
+	// parse them as an alternate .dockercfg
+	if cfg, err := credentialprovider.ReadDockerConfigFileFromUrl(dockerConfigKey, g.Client, metadataHeader); err == nil {
+		return cfg
+	}
+
+	return credentialprovider.DockerConfig{}
+}
+
+// Provide implements DockerConfigProvider
+func (g *dockerConfigUrlKeyProvider) Provide() credentialprovider.DockerConfig {
+	// Read the contents of the google-dockercfg-url key and load a .dockercfg from there
+	if url, err := credentialprovider.ReadUrl(dockerConfigUrlKey, g.Client, metadataHeader); err == nil {
+		if strings.HasPrefix(string(url), "http") {
+			if cfg, err := credentialprovider.ReadDockerConfigFileFromUrl(string(url), g.Client, nil); err == nil {
+				return cfg
+			}
+		} else {
+			// TODO(mattmoor): support reading alternate scheme URLs (e.g. gs:// or s3://)
+			glog.Errorf("Unsupported URL scheme: %s", string(url))
+		}
+	}
+
+	return credentialprovider.DockerConfig{}
+}
+
+// Enabled implements a special metadata-based check, which verifies the
+// storage scope is available on the GCE VM.
+func (g *containerRegistryProvider) Enabled() bool {
+	value, err := credentialprovider.ReadUrl(metadataScopes+"?alt=json", g.Client, metadataHeader)
+	if err != nil {
+		return false
+	}
+	var scopes []string
+	if err := json.Unmarshal([]byte(value), &scopes); err != nil {
+		return false
+	}
+
+	for _, v := range scopes {
+		if strings.HasPrefix(v, storageScopePrefix) {
+			return true
+		}
+	}
+	glog.Warningf("Google container registry is disabled, no storage scope is available: %s", value)
+	return false
+}
+
+// tokenBlob is used to decode the JSON blob containing an access token
+// that is returned by GCE metadata.
+type tokenBlob struct {
+	AccessToken string `json:"access_token"`
+}
+
+// Provide implements DockerConfigProvider
+func (g *containerRegistryProvider) Provide() credentialprovider.DockerConfig {
+	cfg := credentialprovider.DockerConfig{}
+
+	tokenJsonBlob, err := credentialprovider.ReadUrl(metadataToken, g.Client, metadataHeader)
+	if err != nil {
+		return cfg
+	}
+
+	email, err := credentialprovider.ReadUrl(metadataEmail, g.Client, metadataHeader)
+	if err != nil {
+		return cfg
+	}
+
+	var parsedBlob tokenBlob
+	if err := json.Unmarshal([]byte(tokenJsonBlob), &parsedBlob); err != nil {
+		glog.Errorf("while parsing json blob %s: %v", tokenJsonBlob, err)
+		return cfg
+	}
+
+	entry := credentialprovider.DockerConfigEntry{
+		Username: "_token",
+		Password: parsedBlob.AccessToken,
+		Email:    string(email),
+	}
+
+	// Add our entry for each of the supported container registry URLs
+	for _, k := range containerRegistryUrls {
+		cfg[k] = entry
+	}
+	return cfg
+}

pkg/credentialprovider/gcp/metadata_test.go

@@ -0,0 +1,293 @@
+/*
+Copyright 2014 Google Inc. All rights reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package gcp_credentials
+
+import (
+	"encoding/base64"
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"net/http/httptest"
+	"net/url"
+	"reflect"
+	"strings"
+	"testing"
+
+	"github.com/GoogleCloudPlatform/kubernetes/pkg/credentialprovider"
+)
+
+func TestDockerKeyringFromGoogleDockerConfigMetadata(t *testing.T) {
+	registryUrl := "hello.kubernetes.io"
+	email := "foo@bar.baz"
+	username := "foo"
+	password := "bar"
+	auth := base64.StdEncoding.EncodeToString([]byte(fmt.Sprintf("%s:%s", username, password)))
+	sampleDockerConfig := fmt.Sprintf(`{
+   "https://%s": {
+     "email": %q,
+     "auth": %q
+   }
+}`, registryUrl, email, auth)
+
+	const probeEndpoint = "/computeMetadata/v1/"
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		// Only serve the one metadata key.
+		if probeEndpoint == r.URL.Path {
+			w.WriteHeader(http.StatusOK)
+		} else if strings.HasSuffix(dockerConfigKey, r.URL.Path) {
+			w.WriteHeader(http.StatusOK)
+			w.Header().Set("Content-Type", "application/json")
+			fmt.Fprintln(w, sampleDockerConfig)
+		} else {
+			w.WriteHeader(http.StatusNotFound)
+		}
+	}))
+	defer server.Close()
+
+	// Make a transport that reroutes all traffic to the example server
+	transport := &http.Transport{
+		Proxy: func(req *http.Request) (*url.URL, error) {
+			return url.Parse(server.URL + req.URL.Path)
+		},
+	}
+
+	keyring := &credentialprovider.BasicDockerKeyring{}
+	provider := &dockerConfigKeyProvider{
+		metadataProvider{Client: &http.Client{Transport: transport}},
+	}
+
+	if !provider.Enabled() {
+		t.Errorf("Provider is unexpectedly disabled")
+	}
+
+	keyring.Add(provider.Provide())
+
+	val, ok := keyring.Lookup(registryUrl)
+	if !ok {
+		t.Errorf("Didn't find expected URL: %s", registryUrl)
+	}
+
+	if username != val.Username {
+		t.Errorf("Unexpected username value, want: %s, got: %s", username, val.Username)
+	}
+	if password != val.Password {
+		t.Errorf("Unexpected password value, want: %s, got: %s", password, val.Password)
+	}
+	if email != val.Email {
+		t.Errorf("Unexpected email value, want: %s, got: %s", email, val.Email)
+	}
+}
+
+func TestDockerKeyringFromGoogleDockerConfigMetadataUrl(t *testing.T) {
+	registryUrl := "hello.kubernetes.io"
+	email := "foo@bar.baz"
+	username := "foo"
+	password := "bar"
+	auth := base64.StdEncoding.EncodeToString([]byte(fmt.Sprintf("%s:%s", username, password)))
+	sampleDockerConfig := fmt.Sprintf(`{
+   "https://%s": {
+     "email": %q,
+     "auth": %q
+   }
+}`, registryUrl, email, auth)
+
+	const probeEndpoint = "/computeMetadata/v1/"
+	const valueEndpoint = "/my/value"
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		// Only serve the URL key and the value endpoint
+		if probeEndpoint == r.URL.Path {
+			w.WriteHeader(http.StatusOK)
+		} else if valueEndpoint == r.URL.Path {
+			w.WriteHeader(http.StatusOK)
+			w.Header().Set("Content-Type", "application/json")
+			fmt.Fprintln(w, sampleDockerConfig)
+		} else if strings.HasSuffix(dockerConfigUrlKey, r.URL.Path) {
+			w.WriteHeader(http.StatusOK)
+			w.Header().Set("Content-Type", "application/text")
+			fmt.Fprint(w, "http://foo.bar.com"+valueEndpoint)
+		} else {
+			w.WriteHeader(http.StatusNotFound)
+		}
+	}))
+	defer server.Close()
+
+	// Make a transport that reroutes all traffic to the example server
+	transport := &http.Transport{
+		Proxy: func(req *http.Request) (*url.URL, error) {
+			return url.Parse(server.URL + req.URL.Path)
+		},
+	}
+
+	keyring := &credentialprovider.BasicDockerKeyring{}
+	provider := &dockerConfigUrlKeyProvider{
+		metadataProvider{Client: &http.Client{Transport: transport}},
+	}
+
+	if !provider.Enabled() {
+		t.Errorf("Provider is unexpectedly disabled")
+	}
+
+	keyring.Add(provider.Provide())
+
+	val, ok := keyring.Lookup(registryUrl)
+	if !ok {
+		t.Errorf("Didn't find expected URL: %s", registryUrl)
+	}
+
+	if username != val.Username {
+		t.Errorf("Unexpected username value, want: %s, got: %s", username, val.Username)
+	}
+	if password != val.Password {
+		t.Errorf("Unexpected password value, want: %s, got: %s", password, val.Password)
+	}
+	if email != val.Email {
+		t.Errorf("Unexpected email value, want: %s, got: %s", email, val.Email)
+	}
+}
+
+func TestContainerRegistryBasics(t *testing.T) {
+	registryUrl := "container.cloud.google.com"
+	email := "1234@project.gserviceaccount.com"
+	token := &tokenBlob{AccessToken: "ya26.lots-of-indiscernible-garbage"}
+
+	const (
+		defaultEndpoint = "/computeMetadata/v1/instance/service-accounts/default/"
+		scopeEndpoint   = defaultEndpoint + "scopes"
+		emailEndpoint   = defaultEndpoint + "email"
+		tokenEndpoint   = defaultEndpoint + "token"
+	)
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		// Only serve the URL key and the value endpoint
+		if scopeEndpoint == r.URL.Path {
+			w.WriteHeader(http.StatusOK)
+			w.Header().Set("Content-Type", "application/json")
+			fmt.Fprintf(w, `["%s.read_write"]`, storageScopePrefix)
+		} else if emailEndpoint == r.URL.Path {
+			w.WriteHeader(http.StatusOK)
+			fmt.Fprint(w, email)
+		} else if tokenEndpoint == r.URL.Path {
+			w.WriteHeader(http.StatusOK)
+			w.Header().Set("Content-Type", "application/json")
+			bytes, err := json.Marshal(token)
+			if err != nil {
+				t.Fatalf("unexpected error: %+v", err)
+			}
+			fmt.Fprintln(w, string(bytes))
+		} else {
+			w.WriteHeader(http.StatusNotFound)
+		}
+	}))
+	defer server.Close()
+
+	// Make a transport that reroutes all traffic to the example server
+	transport := &http.Transport{
+		Proxy: func(req *http.Request) (*url.URL, error) {
+			return url.Parse(server.URL + req.URL.Path)
+		},
+	}
+
+	keyring := &credentialprovider.BasicDockerKeyring{}
+	provider := &containerRegistryProvider{
+		metadataProvider{Client: &http.Client{Transport: transport}},
+	}
+
+	if !provider.Enabled() {
+		t.Errorf("Provider is unexpectedly disabled")
+	}
+
+	keyring.Add(provider.Provide())
+
+	val, ok := keyring.Lookup(registryUrl)
+	if !ok {
+		t.Errorf("Didn't find expected URL: %s", registryUrl)
+	}
+
+	if "_token" != val.Username {
+		t.Errorf("Unexpected username value, want: %s, got: %s", "_token", val.Username)
+	}
+	if token.AccessToken != val.Password {
+		t.Errorf("Unexpected password value, want: %s, got: %s", token.AccessToken, val.Password)
+	}
+	if email != val.Email {
+		t.Errorf("Unexpected email value, want: %s, got: %s", email, val.Email)
+	}
+}
+
+func TestContainerRegistryNoStorageScope(t *testing.T) {
+	const (
+		defaultEndpoint = "/computeMetadata/v1/instance/service-accounts/default/"
+		scopeEndpoint   = defaultEndpoint + "scopes"
+	)
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		// Only serve the URL key and the value endpoint
+		if scopeEndpoint == r.URL.Path {
+			w.WriteHeader(http.StatusOK)
+			w.Header().Set("Content-Type", "application/json")
+			fmt.Fprint(w, `["https://www.googleapis.com/auth/compute.read_write"]`)
+		} else {
+			w.WriteHeader(http.StatusNotFound)
+		}
+	}))
+	defer server.Close()
+
+	// Make a transport that reroutes all traffic to the example server
+	transport := &http.Transport{
+		Proxy: func(req *http.Request) (*url.URL, error) {
+			return url.Parse(server.URL + req.URL.Path)
+		},
+	}
+
+	provider := &containerRegistryProvider{
+		metadataProvider{Client: &http.Client{Transport: transport}},
+	}
+
+	if provider.Enabled() {
+		t.Errorf("Provider is unexpectedly enabled")
+	}
+}
+
+func TestAllProvidersNoMetadata(t *testing.T) {
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusNotFound)
+	}))
+	defer server.Close()
+
+	// Make a transport that reroutes all traffic to the example server
+	transport := &http.Transport{
+		Proxy: func(req *http.Request) (*url.URL, error) {
+			return url.Parse(server.URL + req.URL.Path)
+		},
+	}
+
+	providers := []credentialprovider.DockerConfigProvider{
+		&dockerConfigKeyProvider{
+			metadataProvider{Client: &http.Client{Transport: transport}},
+		},
+		&dockerConfigUrlKeyProvider{
+			metadataProvider{Client: &http.Client{Transport: transport}},
+		},
+		&containerRegistryProvider{
+			metadataProvider{Client: &http.Client{Transport: transport}},
+		},
+	}
+
+	for _, provider := range providers {
+		if provider.Enabled() {
+			t.Errorf("Provider %s is unexpectedly enabled", reflect.TypeOf(provider).String())
+		}
+	}
+}

pkg/credentialprovider/keyring.go

@@ -0,0 +1,134 @@
+/*
+Copyright 2014 Google Inc. All rights reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package credentialprovider
+
+import (
+	"net/url"
+	"sort"
+	"strings"
+
+	docker "github.com/fsouza/go-dockerclient"
+	"github.com/golang/glog"
+)
+
+// DockerKeyring tracks a set of docker registry credentials, maintaining a
+// reverse index across the registry endpoints. A registry endpoint is made
+// up of a host (e.g. registry.example.com), but it may also contain a path
+// (e.g. registry.example.com/foo) This index is important for two reasons:
+// - registry endpoints may overlap, and when this happens we must find the
+//   most specific match for a given image
+// - iterating a map does not yield predictable results
+type DockerKeyring interface {
+	Lookup(image string) (docker.AuthConfiguration, bool)
+}
+
+// BasicDockerKeyring is a trivial map-backed implementation of DockerKeyring
+type BasicDockerKeyring struct {
+	index []string
+	creds map[string]docker.AuthConfiguration
+}
+
+// lazyDockerKeyring is an implementation of DockerKeyring that lazily
+// materializes its dockercfg based on a set of dockerConfigProviders.
+type lazyDockerKeyring struct {
+	Providers []DockerConfigProvider
+}
+
+func (dk *BasicDockerKeyring) Add(cfg DockerConfig) {
+	if dk.index == nil {
+		dk.index = make([]string, 0)
+		dk.creds = make(map[string]docker.AuthConfiguration)
+	}
+	for loc, ident := range cfg {
+		creds := docker.AuthConfiguration{
+			Username: ident.Username,
+			Password: ident.Password,
+			Email:    ident.Email,
+		}
+
+		parsed, err := url.Parse(loc)
+		if err != nil {
+			glog.Errorf("Entry %q in dockercfg invalid (%v), ignoring", loc, err)
+			continue
+		}
+
+		registry := parsed.Host + parsed.Path
+		dk.creds[registry] = creds
+		dk.index = append(dk.index, registry)
+	}
+
+	// Update the index used to identify which credentials to use for a given
+	// image. The index is reverse-sorted so more specific paths are matched
+	// first. For example, if for the given image "quay.io/coreos/etcd",
+	// credentials for "quay.io/coreos" should match before "quay.io".
+	sort.Sort(sort.Reverse(sort.StringSlice(dk.index)))
+}
+
+const defaultRegistryHost = "index.docker.io/v1/"
+
+// isDefaultRegistryMatch determines whether the given image will
+// pull from the default registry (DockerHub) based on the
+// characteristics of its name.
+func isDefaultRegistryMatch(image string) bool {
+	parts := strings.SplitN(image, "/", 2)
+
+	if len(parts) == 1 {
+		// e.g. library/ubuntu
+		return true
+	}
+
+	// From: http://blog.docker.com/2013/07/how-to-use-your-own-registry/
+	// Docker looks for either a “.” (domain separator) or “:” (port separator)
+	// to learn that the first part of the repository name is a location and not
+	// a user name.
+	return !strings.ContainsAny(parts[0], ".:")
+}
+
+// Lookup implements the DockerKeyring method for fetching credentials
+// based on image name.
+func (dk *BasicDockerKeyring) Lookup(image string) (docker.AuthConfiguration, bool) {
+	// range over the index as iterating over a map does not provide
+	// a predictable ordering
+	for _, k := range dk.index {
+		// NOTE: prefix is a sufficient check because while scheme is allowed,
+		// it is stripped as part of 'Add'
+		if !strings.HasPrefix(image, k) {
+			continue
+		}
+
+		return dk.creds[k], true
+	}
+
+	// Use credentials for the default registry if provided, and appropriate
+	if auth, ok := dk.creds[defaultRegistryHost]; ok && isDefaultRegistryMatch(image) {
+		return auth, true
+	}
+
+	return docker.AuthConfiguration{}, false
+}
+
+// Lookup implements the DockerKeyring method for fetching credentials
+// based on image name.
+func (dk *lazyDockerKeyring) Lookup(image string) (docker.AuthConfiguration, bool) {
+	keyring := &BasicDockerKeyring{}
+
+	for _, p := range dk.Providers {
+		keyring.Add(p.Provide())
+	}
+
+	return keyring.Lookup(image)
+}

pkg/credentialprovider/keyring_test.go

@@ -0,0 +1,261 @@
+/*
+Copyright 2014 Google Inc. All rights reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package credentialprovider
+
+import (
+	"encoding/base64"
+	"fmt"
+	"testing"
+)
+
+func TestDockerKeyringFromBytes(t *testing.T) {
+	url := "hello.kubernetes.io"
+	email := "foo@bar.baz"
+	username := "foo"
+	password := "bar"
+	auth := base64.StdEncoding.EncodeToString([]byte(fmt.Sprintf("%s:%s", username, password)))
+	sampleDockerConfig := fmt.Sprintf(`{
+   "https://%s": {
+     "email": %q,
+     "auth": %q
+   }
+}`, url, email, auth)
+
+	keyring := &BasicDockerKeyring{}
+	if cfg, err := readDockerConfigFileFromBytes([]byte(sampleDockerConfig)); err != nil {
+		t.Errorf("Error processing json blob %q, %v", sampleDockerConfig, err)
+	} else {
+		keyring.Add(cfg)
+	}
+
+	val, ok := keyring.Lookup(url + "/foo/bar")
+	if !ok {
+		t.Errorf("Didn't find expected URL: %s", url)
+	}
+
+	if username != val.Username {
+		t.Errorf("Unexpected username value, want: %s, got: %s", username, val.Username)
+	}
+	if password != val.Password {
+		t.Errorf("Unexpected password value, want: %s, got: %s", password, val.Password)
+	}
+	if email != val.Email {
+		t.Errorf("Unexpected email value, want: %s, got: %s", email, val.Email)
+	}
+}
+
+func TestKeyringMiss(t *testing.T) {
+	url := "hello.kubernetes.io"
+	email := "foo@bar.baz"
+	username := "foo"
+	password := "bar"
+	auth := base64.StdEncoding.EncodeToString([]byte(fmt.Sprintf("%s:%s", username, password)))
+	sampleDockerConfig := fmt.Sprintf(`{
+   "https://%s": {
+     "email": %q,
+     "auth": %q
+   }
+}`, url, email, auth)
+
+	keyring := &BasicDockerKeyring{}
+	if cfg, err := readDockerConfigFileFromBytes([]byte(sampleDockerConfig)); err != nil {
+		t.Errorf("Error processing json blob %q, %v", sampleDockerConfig, err)
+	} else {
+		keyring.Add(cfg)
+	}
+
+	val, ok := keyring.Lookup("world.mesos.org/foo/bar")
+	if ok {
+		t.Errorf("Found unexpected credential: %+v", val)
+	}
+}
+
+func TestKeyringMissWithDockerHubCredentials(t *testing.T) {
+	url := defaultRegistryHost
+	email := "foo@bar.baz"
+	username := "foo"
+	password := "bar"
+	auth := base64.StdEncoding.EncodeToString([]byte(fmt.Sprintf("%s:%s", username, password)))
+	sampleDockerConfig := fmt.Sprintf(`{
+   "https://%s": {
+     "email": %q,
+     "auth": %q
+   }
+}`, url, email, auth)
+
+	keyring := &BasicDockerKeyring{}
+	if cfg, err := readDockerConfigFileFromBytes([]byte(sampleDockerConfig)); err != nil {
+		t.Errorf("Error processing json blob %q, %v", sampleDockerConfig, err)
+	} else {
+		keyring.Add(cfg)
+	}
+
+	val, ok := keyring.Lookup("world.mesos.org/foo/bar")
+	if ok {
+		t.Errorf("Found unexpected credential: %+v", val)
+	}
+}
+
+func TestKeyringHitWithUnqualifiedDockerHub(t *testing.T) {
+	url := defaultRegistryHost
+	email := "foo@bar.baz"
+	username := "foo"
+	password := "bar"
+	auth := base64.StdEncoding.EncodeToString([]byte(fmt.Sprintf("%s:%s", username, password)))
+	sampleDockerConfig := fmt.Sprintf(`{
+   "https://%s": {
+     "email": %q,
+     "auth": %q
+   }
+}`, url, email, auth)
+
+	keyring := &BasicDockerKeyring{}
+	if cfg, err := readDockerConfigFileFromBytes([]byte(sampleDockerConfig)); err != nil {
+		t.Errorf("Error processing json blob %q, %v", sampleDockerConfig, err)
+	} else {
+		keyring.Add(cfg)
+	}
+
+	val, ok := keyring.Lookup("google/docker-registry")
+	if !ok {
+		t.Errorf("Didn't find expected URL: %s", url)
+	}
+
+	if username != val.Username {
+		t.Errorf("Unexpected username value, want: %s, got: %s", username, val.Username)
+	}
+	if password != val.Password {
+		t.Errorf("Unexpected password value, want: %s, got: %s", password, val.Password)
+	}
+	if email != val.Email {
+		t.Errorf("Unexpected email value, want: %s, got: %s", email, val.Email)
+	}
+}
+
+func TestKeyringHitWithUnqualifiedLibraryDockerHub(t *testing.T) {
+	url := defaultRegistryHost
+	email := "foo@bar.baz"
+	username := "foo"
+	password := "bar"
+	auth := base64.StdEncoding.EncodeToString([]byte(fmt.Sprintf("%s:%s", username, password)))
+	sampleDockerConfig := fmt.Sprintf(`{
+   "https://%s": {
+     "email": %q,
+     "auth": %q
+   }
+}`, url, email, auth)
+
+	keyring := &BasicDockerKeyring{}
+	if cfg, err := readDockerConfigFileFromBytes([]byte(sampleDockerConfig)); err != nil {
+		t.Errorf("Error processing json blob %q, %v", sampleDockerConfig, err)
+	} else {
+		keyring.Add(cfg)
+	}
+
+	val, ok := keyring.Lookup("jenkins")
+	if !ok {
+		t.Errorf("Didn't find expected URL: %s", url)
+	}
+
+	if username != val.Username {
+		t.Errorf("Unexpected username value, want: %s, got: %s", username, val.Username)
+	}
+	if password != val.Password {
+		t.Errorf("Unexpected password value, want: %s, got: %s", password, val.Password)
+	}
+	if email != val.Email {
+		t.Errorf("Unexpected email value, want: %s, got: %s", email, val.Email)
+	}
+}
+
+func TestKeyringHitWithQualifiedDockerHub(t *testing.T) {
+	url := defaultRegistryHost
+	email := "foo@bar.baz"
+	username := "foo"
+	password := "bar"
+	auth := base64.StdEncoding.EncodeToString([]byte(fmt.Sprintf("%s:%s", username, password)))
+	sampleDockerConfig := fmt.Sprintf(`{
+   "https://%s": {
+     "email": %q,
+     "auth": %q
+   }
+}`, url, email, auth)
+
+	keyring := &BasicDockerKeyring{}
+	if cfg, err := readDockerConfigFileFromBytes([]byte(sampleDockerConfig)); err != nil {
+		t.Errorf("Error processing json blob %q, %v", sampleDockerConfig, err)
+	} else {
+		keyring.Add(cfg)
+	}
+
+	val, ok := keyring.Lookup(url + "/google/docker-registry")
+	if !ok {
+		t.Errorf("Didn't find expected URL: %s", url)
+	}
+
+	if username != val.Username {
+		t.Errorf("Unexpected username value, want: %s, got: %s", username, val.Username)
+	}
+	if password != val.Password {
+		t.Errorf("Unexpected password value, want: %s, got: %s", password, val.Password)
+	}
+	if email != val.Email {
+		t.Errorf("Unexpected email value, want: %s, got: %s", email, val.Email)
+	}
+}
+
+type testProvider struct {
+	Count int
+}
+
+// Enabled implements dockerConfigProvider
+func (d *testProvider) Enabled() bool {
+	return true
+}
+
+// Provide implements dockerConfigProvider
+func (d *testProvider) Provide() DockerConfig {
+	d.Count += 1
+	return DockerConfig{}
+}
+
+func TestLazyKeyring(t *testing.T) {
+	provider := &testProvider{
+		Count: 0,
+	}
+	lazy := &lazyDockerKeyring{
+		Providers: []DockerConfigProvider{
+			provider,
+		},
+	}
+
+	if provider.Count != 0 {
+		t.Errorf("Unexpected number of Provide calls: %v", provider.Count)
+	}
+	lazy.Lookup("foo")
+	if provider.Count != 1 {
+		t.Errorf("Unexpected number of Provide calls: %v", provider.Count)
+	}
+	lazy.Lookup("foo")
+	if provider.Count != 2 {
+		t.Errorf("Unexpected number of Provide calls: %v", provider.Count)
+	}
+	lazy.Lookup("foo")
+	if provider.Count != 3 {
+		t.Errorf("Unexpected number of Provide calls: %v", provider.Count)
+	}
+}

pkg/credentialprovider/plugins.go

@@ -0,0 +1,62 @@
+/*
+Copyright 2014 Google Inc. All rights reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package credentialprovider
+
+import (
+	"sync"
+
+	"github.com/golang/glog"
+)
+
+// All registered credential providers.
+var providersMutex sync.Mutex
+var providers = make(map[string]DockerConfigProvider)
+
+// RegisterCredentialProvider is called by provider implementations on
+// initialization to register themselves, like so:
+//   func init() {
+//    	RegisterCredentialProvider("name", &myProvider{...})
+//   }
+func RegisterCredentialProvider(name string, provider DockerConfigProvider) {
+	providersMutex.Lock()
+	defer providersMutex.Unlock()
+	_, found := providers[name]
+	if found {
+		glog.Fatalf("Credential provider %q was registered twice", name)
+	}
+	glog.V(1).Infof("Registered credential provider %q", name)
+	providers[name] = provider
+}
+
+// NewDockerKeyring creates a DockerKeyring to use for resolving credentials,
+// which lazily draws from the set of registered credential providers.
+func NewDockerKeyring() DockerKeyring {
+	keyring := &lazyDockerKeyring{
+		Providers: make([]DockerConfigProvider, 0),
+	}
+
+	// TODO(mattmoor): iterating over the map is non-deterministic.  We should
+	// introduce the notion of priorities for conflict resolution.
+	for name, provider := range providers {
+		if provider.Enabled() {
+			glog.Infof("Registering credential provider: %v", name)
+			keyring.Providers = append(keyring.Providers, provider)
+		}
+	}
+
+	return keyring
+}

pkg/credentialprovider/provider.go

@@ -0,0 +1,95 @@
+/*
+Copyright 2014 Google Inc. All rights reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package credentialprovider
+
+import (
+	"os"
+	"reflect"
+	"sync"
+	"time"
+
+	"github.com/golang/glog"
+)
+
+// DockerConfigProvider is the interface that registered extensions implement
+// to materialize 'dockercfg' credentials.
+type DockerConfigProvider interface {
+	Enabled() bool
+	Provide() DockerConfig
+}
+
+// A DockerConfigProvider that simply reads the .dockersfg file
+type defaultDockerConfigProvider struct{}
+
+// init registers our default provider, which simply reads the .dockercfg file.
+func init() {
+	RegisterCredentialProvider(".dockercfg",
+		&CachingDockerConfigProvider{
+			Provider: &defaultDockerConfigProvider{},
+			Lifetime: 5 * time.Minute,
+		})
+}
+
+// CachingDockerConfigProvider implements DockerConfigProvider by composing
+// with another DockerConfigProvider and caching the DockerConfig it provides
+// for a pre-specified lifetime.
+type CachingDockerConfigProvider struct {
+	Provider DockerConfigProvider
+	Lifetime time.Duration
+
+	// cache fields
+	cacheDockerConfig DockerConfig
+	expiration        time.Time
+	mu                sync.Mutex
+}
+
+// Enabled implements dockerConfigProvider
+func (d *defaultDockerConfigProvider) Enabled() bool {
+	return true
+}
+
+// Provide implements dockerConfigProvider
+func (d *defaultDockerConfigProvider) Provide() DockerConfig {
+	// Read the standard Docker credentials from .dockercfg
+	if cfg, err := ReadDockerConfigFile(); err == nil {
+		return cfg
+	} else if !os.IsNotExist(err) {
+		glog.V(1).Infof("Unable to parse Docker config file: %v", err)
+	}
+	return DockerConfig{}
+}
+
+// Enabled implements dockerConfigProvider
+func (d *CachingDockerConfigProvider) Enabled() bool {
+	return d.Provider.Enabled()
+}
+
+// Provide implements dockerConfigProvider
+func (d *CachingDockerConfigProvider) Provide() DockerConfig {
+	d.mu.Lock()
+	defer d.mu.Unlock()
+
+	// If the cache hasn't expired, return our cache
+	if time.Now().Before(d.expiration) {
+		return d.cacheDockerConfig
+	}
+
+	glog.Infof("Refreshing cache for provider: %v", reflect.TypeOf(d.Provider).String())
+	d.cacheDockerConfig = d.Provider.Provide()
+	d.expiration = time.Now().Add(d.Lifetime)
+	return d.cacheDockerConfig
+}

pkg/credentialprovider/provider_test.go

@@ -0,0 +1,62 @@
+/*
+Copyright 2014 Google Inc. All rights reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package credentialprovider
+
+import (
+	"testing"
+	"time"
+)
+
+func TestCachingProvider(t *testing.T) {
+	provider := &testProvider{
+		Count: 0,
+	}
+
+	cache := &CachingDockerConfigProvider{
+		Provider: provider,
+		Lifetime: 1 * time.Second,
+	}
+
+	if provider.Count != 0 {
+		t.Errorf("Unexpected number of Provide calls: %v", provider.Count)
+	}
+	cache.Provide()
+	cache.Provide()
+	cache.Provide()
+	cache.Provide()
+	if provider.Count != 1 {
+		t.Errorf("Unexpected number of Provide calls: %v", provider.Count)
+	}
+
+	time.Sleep(cache.Lifetime)
+	cache.Provide()
+	cache.Provide()
+	cache.Provide()
+	cache.Provide()
+	if provider.Count != 2 {
+		t.Errorf("Unexpected number of Provide calls: %v", provider.Count)
+	}
+
+	time.Sleep(cache.Lifetime)
+	cache.Provide()
+	cache.Provide()
+	cache.Provide()
+	cache.Provide()
+	if provider.Count != 3 {
+		t.Errorf("Unexpected number of Provide calls: %v", provider.Count)
+	}
+}

pkg/kubelet/dockertools/docker.go

@@ -25,15 +25,14 @@ import (
 	"io"
 	"io/ioutil"
 	"math/rand"
-	"os"
 	"os/exec"
-	"sort"
 	"strconv"
 	"strings"
 
 	"github.com/GoogleCloudPlatform/kubernetes/pkg/api"
+	"github.com/GoogleCloudPlatform/kubernetes/pkg/credentialprovider"
 	"github.com/GoogleCloudPlatform/kubernetes/pkg/util"
-	"github.com/fsouza/go-dockerclient"
+	docker "github.com/fsouza/go-dockerclient"
 	"github.com/golang/glog"
 )
 
@@ -65,7 +64,7 @@ type DockerPuller interface {
 // dockerPuller is the default implementation of DockerPuller.
 type dockerPuller struct {
 	client  DockerInterface
-	keyring *dockerKeyring
+	keyring credentialprovider.DockerKeyring
 }
 
 type throttledDockerPuller struct {
@@ -77,19 +76,9 @@ type throttledDockerPuller struct {
 func NewDockerPuller(client DockerInterface, qps float32, burst int) DockerPuller {
 	dp := dockerPuller{
 		client:  client,
-		keyring: newDockerKeyring(),
+		keyring: credentialprovider.NewDockerKeyring(),
 	}
 
-	cfg, err := readDockerConfigFile()
-	if err == nil {
-		cfg.addToKeyring(dp.keyring)
-	} else if !os.IsNotExist(err) {
-		glog.V(1).Infof("Unable to parse Docker config file: %v", err)
-	}
-
-	if dp.keyring.count() == 0 {
-		glog.V(1).Infof("Continuing with empty Docker keyring")
-	}
 	if qps == 0.0 {
 		return dp
 	}
@@ -218,7 +207,7 @@ func (p dockerPuller) Pull(image string) error {
 		Tag:        tag,
 	}
 
-	creds, ok := p.keyring.lookup(image)
+	creds, ok := p.keyring.Lookup(image)
 	if !ok {
 		glog.V(1).Infof("Pulling image %s without credentials", image)
 	}
@@ -608,62 +597,3 @@ func parseImageName(image string) (string, string) {
 type ContainerCommandRunner interface {
 	RunInContainer(containerID string, cmd []string) ([]byte, error)
 }
-
-// dockerKeyring tracks a set of docker registry credentials, maintaining a
-// reverse index across the registry endpoints. A registry endpoint is made
-// up of a host (e.g. registry.example.com), but it may also contain a path
-// (e.g. registry.example.com/foo) This index is important for two reasons:
-// - registry endpoints may overlap, and when this happens we must find the
-//   most specific match for a given image
-// - iterating a map does not yield predictable results
-type dockerKeyring struct {
-	index []string
-	creds map[string]docker.AuthConfiguration
-}
-
-func newDockerKeyring() *dockerKeyring {
-	return &dockerKeyring{
-		index: make([]string, 0),
-		creds: make(map[string]docker.AuthConfiguration),
-	}
-}
-
-func (dk *dockerKeyring) add(registry string, creds docker.AuthConfiguration) {
-	dk.creds[registry] = creds
-
-	dk.index = append(dk.index, registry)
-	dk.reindex()
-}
-
-// reindex updates the index used to identify which credentials to use for
-// a given image. The index is reverse-sorted so more specific paths are
-// matched first. For example, if for the given image "quay.io/coreos/etcd",
-// credentials for "quay.io/coreos" should match before "quay.io".
-func (dk *dockerKeyring) reindex() {
-	sort.Sort(sort.Reverse(sort.StringSlice(dk.index)))
-}
-
-const defaultRegistryHost = "index.docker.io/v1/"
-
-func (dk *dockerKeyring) lookup(image string) (docker.AuthConfiguration, bool) {
-	// range over the index as iterating over a map does not provide
-	// a predictable ordering
-	for _, k := range dk.index {
-		if !strings.HasPrefix(image, k) {
-			continue
-		}
-
-		return dk.creds[k], true
-	}
-
-	// use credentials for the default registry if provided
-	if auth, ok := dk.creds[defaultRegistryHost]; ok {
-		return auth, true
-	}
-
-	return docker.AuthConfiguration{}, false
-}
-
-func (dk dockerKeyring) count() int {
-	return len(dk.creds)
-}

pkg/kubelet/dockertools/docker_test.go

@@ -23,7 +23,8 @@ import (
 	"testing"
 
 	"github.com/GoogleCloudPlatform/kubernetes/pkg/api"
-	"github.com/fsouza/go-dockerclient"
+	"github.com/GoogleCloudPlatform/kubernetes/pkg/credentialprovider"
+	docker "github.com/fsouza/go-dockerclient"
 )
 
 func verifyCalls(t *testing.T, fakeDocker *FakeDockerClient, calls []string) {
@@ -213,9 +214,19 @@ func TestDockerKeyringLookup(t *testing.T) {
 		Email:    "grace@example.com",
 	}
 
-	dk := newDockerKeyring()
-	dk.add("bar.example.com/pong", grace)
-	dk.add("bar.example.com", ada)
+	dk := &credentialprovider.BasicDockerKeyring{}
+	dk.Add(credentialprovider.DockerConfig{
+		"bar.example.com/pong": credentialprovider.DockerConfigEntry{
+			Username: grace.Username,
+			Password: grace.Password,
+			Email:    grace.Email,
+		},
+		"bar.example.com": credentialprovider.DockerConfigEntry{
+			Username: ada.Username,
+			Password: ada.Password,
+			Email:    ada.Email,
+		},
+	})
 
 	tests := []struct {
 		image string
@@ -243,7 +254,7 @@ func TestDockerKeyringLookup(t *testing.T) {
 	}
 
 	for i, tt := range tests {
-		match, ok := dk.lookup(tt.image)
+		match, ok := dk.Lookup(tt.image)
 		if tt.ok != ok {
 			t.Errorf("case %d: expected ok=%t, got %t", i, tt.ok, ok)
 		}

pkg/standalone/standalone.go

@@ -38,7 +38,7 @@ import (
 	"github.com/GoogleCloudPlatform/kubernetes/plugin/pkg/scheduler"
 	"github.com/GoogleCloudPlatform/kubernetes/plugin/pkg/scheduler/factory"
 
-	"github.com/fsouza/go-dockerclient"
+	docker "github.com/fsouza/go-dockerclient"
 	"github.com/golang/glog"
 )