Persist cache image in build

pkg/apis/build/v1alpha1/build.go

@@ -96,6 +96,17 @@ func (b *Build) BuiltImage() string {
 	return b.Status.LatestImage
 }
 
+func (b *Build) CacheImage() string {
+	if b == nil {
+		return ""
+	}
+	if !b.IsSuccess() {
+		return ""
+	}
+
+	return b.Status.LatestCacheImage
+}
+
 func (b *Build) IsSuccess() bool {
 	if b == nil {
 		return false

pkg/apis/build/v1alpha1/build_types.go

@@ -86,8 +86,9 @@ type Binding struct {
 
 // +k8s:openapi-gen=true
 type LastBuild struct {
-	Image   string `json:"image,omitempty"`
-	StackId string `json:"stackId,omitempty"`
+	Image      string `json:"image,omitempty"`
+	CacheImage string `json:"cacheImage,omitempty"`
+	StackId    string `json:"stackId,omitempty"`
 }
 
 // +k8s:openapi-gen=true
@@ -102,6 +103,7 @@ type BuildStatus struct {
 	BuildMetadata       BuildpackMetadataList `json:"buildMetadata,omitempty"`
 	Stack               BuildStack            `json:"stack,omitempty"`
 	LatestImage         string                `json:"latestImage,omitempty"`
+	LatestCacheImage    string                `json:"latestCacheImage,omitempty"`
 	PodName             string                `json:"podName,omitempty"`
 	// +listType
 	StepStates []corev1.ContainerState `json:"stepStates,omitempty"`

pkg/apis/build/v1alpha1/image_builds.go

@@ -96,8 +96,9 @@ func lastBuild(latestBuild *Build) *LastBuild {
 	}
 
 	return &LastBuild{
-		Image:   latestBuild.BuiltImage(),
-		StackId: latestBuild.Stack(),
+		Image:      latestBuild.BuiltImage(),
+		CacheImage: latestBuild.CacheImage(),
+		StackId:    latestBuild.Stack(),
 	}
 }
 

pkg/cnb/cnb_metadata.go

@@ -53,6 +53,28 @@ func (r *RemoteMetadataRetriever) GetBuiltImage(ctx context.Context, build *v1al
 	return readBuiltImage(appImage, appImageId)
 }
 
+func (r *RemoteMetadataRetriever) GetCacheImage(ctx context.Context, build *v1alpha1.Build) (string, error) {
+	if len(build.Spec.Cache.ImageTag) == 0 {
+		return "", nil
+	}
+
+	keychain, err := r.KeychainFactory.KeychainForSecretRef(ctx, registry.SecretRef{
+		ServiceAccount: build.Spec.ServiceAccount,
+		Namespace:      build.Namespace,
+	})
+
+	if err != nil {
+		return "", err
+	}
+
+	_, cacheImageId, err := r.ImageFetcher.Fetch(keychain, build.Spec.Cache.ImageTag)
+	if err != nil {
+		return "", errors.Wrap(err, "unable to fetch cache image")
+	}
+
+	return cacheImageId, nil
+}
+
 type BuiltImage struct {
 	Identifier        string
 	CompletedAt       time.Time

pkg/reconciler/build/build.go

@@ -31,6 +31,7 @@ const (
 //go:generate counterfeiter . MetadataRetriever
 type MetadataRetriever interface {
 	GetBuiltImage(context.Context, *v1alpha1.Build) (cnb.BuiltImage, error)
+	GetCacheImage(context.Context, *v1alpha1.Build) (string, error)
 }
 
 type PodGenerator interface {
@@ -110,8 +111,14 @@ func (c *Reconciler) reconcile(ctx context.Context, build *v1alpha1.Build) error
 			return err
 		}
 
+		cacheImageId, err := c.MetadataRetriever.GetCacheImage(ctx, build)
+		if err != nil {
+			return err
+		}
+
 		build.Status.BuildMetadata = buildMetadataFromBuiltImage(image)
 		build.Status.LatestImage = image.Identifier
+		build.Status.LatestCacheImage = cacheImageId
 		build.Status.Stack.RunImage = image.Stack.RunImage
 		build.Status.Stack.ID = image.Stack.ID
 	}