Whitelist label ts using registry cache decorator

cmd/fluxd/main.go

@@ -146,6 +146,7 @@ func main() {
 		registryTrace        = fs.Bool("registry-trace", false, "output trace of image registry requests to log")
 		registryInsecure     = fs.StringSlice("registry-insecure-host", []string{}, "let these registry hosts skip TLS host verification and fall back to using HTTP instead of HTTPS; this allows man-in-the-middle attacks, so use with extreme caution")
 		registryExcludeImage = fs.StringSlice("registry-exclude-image", []string{"k8s.gcr.io/*"}, "do not scan images that match these glob expressions; the default is to exclude the 'k8s.gcr.io/*' images")
+		registryUseLabels    = fs.StringSlice("registry-use-labels", []string{"index.docker.io/weaveworks/*"}, "use the timestamp (RFC3339) from labels for (canonical) image refs that match these glob expression")
 
 		// AWS authentication
 		registryAWSRegions         = fs.StringSlice("registry-ecr-region", nil, "include just these AWS regions when scanning images in ECR; when not supplied, the cluster's region will included if it can be detected through the AWS API")
@@ -498,6 +499,9 @@ func main() {
 
 		cacheRegistry = &cache.Cache{
 			Reader: cacheClient,
+			Decorators: []cache.Decorator{
+				cache.TimestampLabelWhitelist(*registryUseLabels),
+			},
 		}
 		cacheRegistry = registry.NewInstrumentedRegistry(cacheRegistry)
 

registry/cache/registry.go

@@ -5,6 +5,7 @@ import (
 	"time"
 
 	"github.com/pkg/errors"
+	"github.com/ryanuber/go-glob"
 
 	fluxerr "github.com/weaveworks/flux/errors"
 	"github.com/weaveworks/flux/image"
@@ -28,7 +29,41 @@ repository.
 
 // Cache is a local cache of image metadata.
 type Cache struct {
-	Reader Reader
+	Reader     Reader
+	Decorators []Decorator
+}
+
+// Decorator is for decorating an ImageRepository before it is returned.
+type Decorator interface {
+	apply(*ImageRepository)
+}
+
+// TimestampLabelWhitelist contains a string slice of glob patterns. Any
+// canonical image reference that matches one of the glob patterns will
+// prefer creation timestamps from labels over the one it received from
+// the registry.
+type TimestampLabelWhitelist []string
+
+// apply checks if any of the canonical image references from the
+// repository matches a glob pattern from the list. If it does, and the
+// image record has a valid timestamp label, it will replace the Created
+// field with the value from the label.
+func (l TimestampLabelWhitelist) apply(r *ImageRepository) {
+	for k, i := range r.Images {
+		for _, exp := range l {
+			if !glob.Glob(exp, i.ID.CanonicalName().String()) {
+				continue
+			}
+
+			switch {
+			case !i.Labels.Created.IsZero():
+				i.CreatedAt = i.Labels.Created
+			case !i.Labels.BuildDate.IsZero():
+				i.CreatedAt = i.Labels.BuildDate
+			}
+			r.Images[k] = i
+		}
+	}
 }
 
 // GetImageRepositoryMetadata returns the metadata from an image
@@ -53,6 +88,11 @@ func (c *Cache) GetImageRepositoryMetadata(id image.Name) (image.RepositoryMetad
 		return image.RepositoryMetadata{}, ErrNotCached
 	}
 
+	// (Maybe) decorate the image repository.
+	for _, d := range c.Decorators {
+		d.apply(&repo)
+	}
+
 	return repo.RepositoryMetadata, nil
 }