Pin image by digest on service create and update

Signed-off-by: Nishant Totla <nishanttotla@gmail.com>

daemon/cluster/cluster.go

@@ -1,6 +1,7 @@
 package cluster
 
 import (
+	"encoding/base64"
 	"encoding/json"
 	"fmt"
 	"io/ioutil"
@@ -26,6 +27,7 @@ import (
 	"github.com/docker/docker/opts"
 	"github.com/docker/docker/pkg/ioutils"
 	"github.com/docker/docker/pkg/signal"
+	"github.com/docker/docker/reference"
 	"github.com/docker/docker/runconfig"
 	swarmapi "github.com/docker/swarmkit/api"
 	swarmnode "github.com/docker/swarmkit/node"
@@ -871,6 +873,46 @@ func (c *Cluster) GetServices(options apitypes.ServiceListOptions) ([]types.Serv
 	return services, nil
 }
 
+// imageWithDigestString takes an image such as name or name:tag
+// and returns the image pinned to a digest, such as name@sha256:34234...
+func (c *Cluster) imageWithDigestString(ctx context.Context, image string, authConfig *apitypes.AuthConfig) (string, error) {
+	ref, err := reference.ParseNamed(image)
+	if err != nil {
+		return "", err
+	}
+	// only query registry if not a canonical reference (i.e. with digest)
+	if _, ok := ref.(reference.Canonical); !ok {
+		ref = reference.WithDefaultTag(ref)
+
+		namedTaggedRef, ok := ref.(reference.NamedTagged)
+		if !ok {
+			return "", fmt.Errorf("unable to cast image to NamedTagged reference object")
+		}
+
+		repo, _, err := c.config.Backend.GetRepository(ctx, namedTaggedRef, authConfig)
+		if err != nil {
+			return "", err
+		}
+		dscrptr, err := repo.Tags(ctx).Get(ctx, namedTaggedRef.Tag())
+		if err != nil {
+			return "", err
+		}
+
+		// TODO(nishanttotla): Currently, the service would lose the tag while calling WithDigest
+		// To prevent this, we create the image string manually, which is a bad idea in general
+		// This will be fixed when https://github.com/docker/distribution/pull/2044 is vendored
+		// namedDigestedRef, err := reference.WithDigest(ref, dscrptr.Digest)
+		// if err != nil {
+		// 	return "", err
+		// }
+		// return namedDigestedRef.String(), nil
+		return image + "@" + dscrptr.Digest.String(), nil
+	} else {
+		// reference already contains a digest, so just return it
+		return ref.String(), nil
+	}
+}
+
 // CreateService creates a new service in a managed swarm cluster.
 func (c *Cluster) CreateService(s types.ServiceSpec, encodedAuth string) (string, error) {
 	c.RLock()
@@ -893,14 +935,33 @@ func (c *Cluster) CreateService(s types.ServiceSpec, encodedAuth string) (string
 		return "", err
 	}
 
+	ctnr := serviceSpec.Task.GetContainer()
+	if ctnr == nil {
+		return "", fmt.Errorf("service does not use container tasks")
+	}
+
 	if encodedAuth != "" {
-		ctnr := serviceSpec.Task.GetContainer()
-		if ctnr == nil {
-			return "", fmt.Errorf("service does not use container tasks")
-		}
 		ctnr.PullOptions = &swarmapi.ContainerSpec_PullOptions{RegistryAuth: encodedAuth}
 	}
 
+	// retrieve auth config from encoded auth
+	authConfig := &apitypes.AuthConfig{}
+	if encodedAuth != "" {
+		if err := json.NewDecoder(base64.NewDecoder(base64.URLEncoding, strings.NewReader(encodedAuth))).Decode(authConfig); err != nil {
+			logrus.Warnf("invalid authconfig: %v", err)
+		}
+	}
+	// pin image by digest
+	if os.Getenv("DOCKER_SERVICE_PREFER_OFFLINE_IMAGE") != "1" {
+		digestImage, err := c.imageWithDigestString(ctx, ctnr.Image, authConfig)
+		if err != nil {
+			logrus.Warnf("unable to pin image %s to digest: %s", ctnr.Image, err.Error())
+		} else {
+			logrus.Debugf("pinning image %s by digest: %s", ctnr.Image, digestImage)
+			ctnr.Image = digestImage
+		}
+	}
+
 	r, err := c.client.CreateService(ctx, &swarmapi.CreateServiceRequest{Spec: &serviceSpec})
 	if err != nil {
 		return "", err
@@ -955,12 +1016,13 @@ func (c *Cluster) UpdateService(serviceIDOrName string, version uint64, spec typ
 		return err
 	}
 
+	newCtnr := serviceSpec.Task.GetContainer()
+	if newCtnr == nil {
+		return fmt.Errorf("service does not use container tasks")
+	}
+
 	if encodedAuth != "" {
-		ctnr := serviceSpec.Task.GetContainer()
-		if ctnr == nil {
-			return fmt.Errorf("service does not use container tasks")
-		}
-		ctnr.PullOptions = &swarmapi.ContainerSpec_PullOptions{RegistryAuth: encodedAuth}
+		newCtnr.PullOptions = &swarmapi.ContainerSpec_PullOptions{RegistryAuth: encodedAuth}
 	} else {
 		// this is needed because if the encodedAuth isn't being updated then we
 		// shouldn't lose it, and continue to use the one that was already present
@@ -979,7 +1041,29 @@ func (c *Cluster) UpdateService(serviceIDOrName string, version uint64, spec typ
 		if ctnr == nil {
 			return fmt.Errorf("service does not use container tasks")
 		}
-		serviceSpec.Task.GetContainer().PullOptions = ctnr.PullOptions
+		newCtnr.PullOptions = ctnr.PullOptions
+		// update encodedAuth so it can be used to pin image by digest
+		if ctnr.PullOptions != nil {
+			encodedAuth = ctnr.PullOptions.RegistryAuth
+		}
+	}
+
+	// retrieve auth config from encoded auth
+	authConfig := &apitypes.AuthConfig{}
+	if encodedAuth != "" {
+		if err := json.NewDecoder(base64.NewDecoder(base64.URLEncoding, strings.NewReader(encodedAuth))).Decode(authConfig); err != nil {
+			logrus.Warnf("invalid authconfig: %v", err)
+		}
+	}
+	// pin image by digest
+	if os.Getenv("DOCKER_SERVICE_PREFER_OFFLINE_IMAGE") != "1" {
+		digestImage, err := c.imageWithDigestString(ctx, newCtnr.Image, authConfig)
+		if err != nil {
+			logrus.Warnf("unable to pin image %s to digest: %s", newCtnr.Image, err.Error())
+		} else if newCtnr.Image != digestImage {
+			logrus.Debugf("pinning image %s by digest: %s", newCtnr.Image, digestImage)
+			newCtnr.Image = digestImage
+		}
 	}
 
 	_, err = c.client.UpdateService(

daemon/cluster/executor/backend.go

@@ -4,6 +4,7 @@ import (
 	"io"
 	"time"
 
+	"github.com/docker/distribution"
 	"github.com/docker/docker/api/types"
 	"github.com/docker/docker/api/types/container"
 	"github.com/docker/docker/api/types/events"
@@ -45,5 +46,5 @@ type Backend interface {
 	UnsubscribeFromEvents(listener chan interface{})
 	UpdateAttachment(string, string, string, *network.NetworkingConfig) error
 	WaitForDetachment(context.Context, string, string, string, string) error
-	ResolveTagToDigest(context.Context, reference.NamedTagged, *types.AuthConfig) (string, error)
+	GetRepository(context.Context, reference.NamedTagged, *types.AuthConfig) (distribution.Repository, bool, error)
 }

daemon/image_pull.go

@@ -4,6 +4,7 @@ import (
 	"io"
 	"strings"
 
+	dist "github.com/docker/distribution"
 	"github.com/docker/distribution/digest"
 	"github.com/docker/docker/api/types"
 	"github.com/docker/docker/builder"
@@ -105,40 +106,39 @@ func (daemon *Daemon) pullImageWithReference(ctx context.Context, ref reference.
 	return err
 }
 
-func (daemon *Daemon) ResolveTagToDigest(ctx context.Context, ref reference.NamedTagged, authConfig *types.AuthConfig) (string, error) {
+func (daemon *Daemon) GetRepository(ctx context.Context, ref reference.NamedTagged, authConfig *types.AuthConfig) (dist.Repository, bool, error) {
 	// get repository info
 	repoInfo, err := daemon.RegistryService.ResolveRepository(ref)
 	if err != nil {
-		return "", err
+		return nil, false, err
 	}
 	// makes sure name is not empty or `scratch`
 	if err := distribution.ValidateRepoName(repoInfo.Name()); err != nil {
-		return "", err
+		return nil, false, err
 	}
 
 	// get endpoints
 	endpoints, err := daemon.RegistryService.LookupPullEndpoints(repoInfo.Hostname())
 	if err != nil {
-		return "", err
+		return nil, false, err
 	}
 
 	// retrieve repository
-	// TODO(nishanttotla): More sophisticated selection of endpoint
-	repo, confirmedV2, err := distribution.NewV2Repository(ctx, repoInfo, endpoints[0], nil, authConfig, "pull")
-
-	if err != nil {
-		return "", err
-	}
-	digest := ""
+	var (
+		confirmedV2 bool
+		repository  dist.Repository
+		lastError   error
+	)
+
+	for _, endpoint := range endpoints {
+		if endpoint.Version == registry.APIVersion1 {
+			continue
+		}
 
-	// only retrieve digest if the repo is v2
-	if confirmedV2 {
-		dscrptr, err := repo.Tags(ctx).Get(ctx, ref.Tag())
-		if err != nil {
-			return "", err
-		} else {
-			digest = dscrptr.Digest.String()
+		repository, confirmedV2, lastError = distribution.NewV2Repository(ctx, repoInfo, endpoint, nil, authConfig, "pull")
+		if lastError == nil && confirmedV2 {
+			break
 		}
 	}
-	return digest, nil
+	return repository, confirmedV2, lastError
 }