Include changes from feedback

Use constructor for ecrProvider
Rename package to "credentials" like golint requests
Don't wrap the lazy provider with a caching provider
Add immedita compile-time interface conformance checks for the interfaces
Added comments

pkg/cloudprovider/providers/aws/aws.go

@@ -42,7 +42,7 @@ import (
 
 	"k8s.io/kubernetes/pkg/api"
 	"k8s.io/kubernetes/pkg/cloudprovider"
-	"k8s.io/kubernetes/pkg/credentialprovider/aws"
+	aws_credentials "k8s.io/kubernetes/pkg/credentialprovider/aws"
 	"k8s.io/kubernetes/pkg/types"
 
 	"github.com/golang/glog"

pkg/credentialprovider/aws/aws_credentials.go

@@ -14,7 +14,7 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-package aws_credentials
+package credentials
 
 import (
 	"encoding/base64"
@@ -84,6 +84,8 @@ type lazyEcrProvider struct {
 	actualProvider *credentialprovider.CachingDockerConfigProvider
 }
 
+var _ credentialprovider.DockerConfigProvider = &lazyEcrProvider{}
+
 // ecrProvider is a DockerConfigProvider that gets and refreshes 12-hour tokens
 // from AWS to access ECR.
 type ecrProvider struct {
@@ -92,6 +94,8 @@ type ecrProvider struct {
 	getter    tokenGetter
 }
 
+var _ credentialprovider.DockerConfigProvider = &ecrProvider{}
+
 // Init creates a lazy provider for each AWS region, in order to support
 // cross-region ECR access. They have to be lazy because it's unlikely, but not
 // impossible, that we'll use more than one.
@@ -101,20 +105,17 @@ type ecrProvider struct {
 func Init() {
 	for _, region := range AWSRegions {
 		credentialprovider.RegisterCredentialProvider("aws-ecr-"+region,
-			&credentialprovider.CachingDockerConfigProvider{
-				Provider: &lazyEcrProvider{
+			&lazyEcrProvider{
 				region:    region,
 				regionURL: fmt.Sprintf(registryURLTemplate, region),
-				},
-				// This is going to be just a lazy proxy to the real ecrProvider.
-				// It holds no real credentials, so refresh practically never.
-				Lifetime: 365 * 24 * time.Hour,
 			})
 	}
 
 }
 
 // Enabled implements DockerConfigProvider.Enabled for the lazy provider.
+// Since we perform no checks/work of our own and actualProvider is only created
+// later at image pulling time (if ever), always return true.
 func (p *lazyEcrProvider) Enabled() bool {
 	return true
 }
@@ -126,15 +127,11 @@ func (p *lazyEcrProvider) LazyProvide() *credentialprovider.DockerConfigEntry {
 	if p.actualProvider == nil {
 		glog.V(2).Infof("Creating ecrProvider for %s", p.region)
 		p.actualProvider = &credentialprovider.CachingDockerConfigProvider{
-			Provider: &ecrProvider{
-				region: p.region,
-				regionURL: p.regionURL,
-			},
+			Provider: newEcrProvider(p.region, nil),
 			// Refresh credentials a little earlier than expiration time
 			Lifetime: 11*time.Hour + 55*time.Minute,
 		}
 		if !p.actualProvider.Enabled() {
-
 			return nil
 		}
 	}
@@ -153,6 +150,14 @@ func (p *lazyEcrProvider) Provide() credentialprovider.DockerConfig {
 	return cfg
 }
 
+func newEcrProvider(region string, getter tokenGetter) *ecrProvider {
+	return &ecrProvider{
+		region:    region,
+		regionURL: fmt.Sprintf(registryURLTemplate, region),
+		getter:    getter,
+	}
+}
+
 // Enabled implements DockerConfigProvider.Enabled for the AWS token-based implementation.
 // For now, it gets activated only if AWS was chosen as the cloud provider.
 // TODO: figure how to enable it manually for deployments that are not on AWS but still

pkg/credentialprovider/aws/aws_credentials_test.go

@@ -14,7 +14,7 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-package aws_credentials
+package credentials
 
 import (
 	"encoding/base64"
@@ -64,14 +64,12 @@ func TestEcrProvide(t *testing.T) {
 	}
 	image := "foo/bar"
 
-	provider := &ecrProvider{
-		region: "lala-land-1",
-		regionURL: "*.dkr.ecr.lala-land-1.amazonaws.com",
-		getter: &testTokenGetter{
+	provider := newEcrProvider("lala-land-1",
+		&testTokenGetter{
 			user:     user,
 			password: password,
-			endpoint: registry},
-	}
+			endpoint: registry,
+		})
 
 	keyring := &credentialprovider.BasicDockerKeyring{}
 	keyring.Add(provider.Provide())