ft: allow detect changes local images

pkg/container/client.go

@@ -311,6 +311,10 @@ func (client dockerClient) RenameContainer(c t.Container, newName string) error
 func (client dockerClient) IsContainerStale(container t.Container) (stale bool, latestImage t.ImageID, err error) {
 	ctx := context.Background()
 
+	if isLocalImage, checkErr := container.LocalImage(); checkErr && isLocalImage {
+		return client.HasNewImage(ctx, container)
+	}
+
 	if !client.PullImages || container.IsNoPull() {
 		log.Debugf("Skipping image pull.")
 	} else if err := client.PullImage(ctx, container); err != nil {

pkg/container/container.go

@@ -113,6 +113,22 @@ func (c Container) ImageName() string {
 	return imageName
 }
 
+// Local returns the value of the container local label and if the label
+// was set.
+func (c Container) LocalImage() (bool, bool) {
+	rawBool, ok := c.getLabelValue(enableLocal)
+	if !ok {
+		return false, false
+	}
+
+	parsedBool, err := strconv.ParseBool(rawBool)
+	if err != nil {
+		return false, false
+	}
+
+	return parsedBool, true
+}
+
 // Enabled returns the value of the container enabled label and if the label
 // was set.
 func (c Container) Enabled() (bool, bool) {

pkg/container/metadata.go

@@ -4,6 +4,7 @@ const (
 	watchtowerLabel        = "com.centurylinklabs.watchtower"
 	signalLabel            = "com.centurylinklabs.watchtower.stop-signal"
 	enableLabel            = "com.centurylinklabs.watchtower.enable"
+	enableLocal            = "com.centurylinklabs.watchtower.local-image"
 	monitorOnlyLabel       = "com.centurylinklabs.watchtower.monitor-only"
 	noPullLabel            = "com.centurylinklabs.watchtower.no-pull"
 	dependsOnLabel         = "com.centurylinklabs.watchtower.depends-on"

pkg/types/container.go

@@ -75,4 +75,5 @@ type Container interface {
 	IsRestarting() bool
 	GetCreateConfig() *dc.Config
 	GetCreateHostConfig() *dc.HostConfig
+	LocalImage() (bool, bool)
 }