clean-up "resolve image" option logic

- change `validateResolveImageFlag()` to only perform _validation_,
  and not combine it with modifying the option.
- use a `switch` instead of `if` in `validateResolveImageFlag()`
- `deployServices()`: break up some `switch` cases to make them
  easier to read/understand the logic.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

cli/command/stack/swarm/deploy.go

@@ -25,25 +25,26 @@ const (
 func RunDeploy(dockerCli command.Cli, opts options.Deploy, cfg *composetypes.Config) error {
 	ctx := context.Background()
 
-	if err := validateResolveImageFlag(dockerCli, &opts); err != nil {
+	if err := validateResolveImageFlag(&opts); err != nil {
 		return err
 	}
-
-	return deployCompose(ctx, dockerCli, opts, cfg)
-}
-
-// validateResolveImageFlag validates the opts.resolveImage command line option
-// and also turns image resolution off if the version is older than 1.30
-func validateResolveImageFlag(dockerCli command.Cli, opts *options.Deploy) error {
-	if opts.ResolveImage != ResolveImageAlways && opts.ResolveImage != ResolveImageChanged && opts.ResolveImage != ResolveImageNever {
-		return errors.Errorf("Invalid option %s for flag --resolve-image", opts.ResolveImage)
-	}
 	// client side image resolution should not be done when the supported
 	// server version is older than 1.30
 	if versions.LessThan(dockerCli.Client().ClientVersion(), "1.30") {
 		opts.ResolveImage = ResolveImageNever
 	}
+
+	return deployCompose(ctx, dockerCli, opts, cfg)
+}
+
+// validateResolveImageFlag validates the opts.resolveImage command line option
+func validateResolveImageFlag(opts *options.Deploy) error {
+	switch opts.ResolveImage {
+	case ResolveImageAlways, ResolveImageChanged, ResolveImageNever:
 		return nil
+	default:
+		return errors.Errorf("Invalid option %s for flag --resolve-image", opts.ResolveImage)
+	}
 }
 
 // checkDaemonIsSwarmManager does an Info API call to verify that the daemon is

cli/command/stack/swarm/deploy_composefile.go

@@ -192,6 +192,7 @@ func createNetworks(
 	return nil
 }
 
+// nolint: gocyclo
 func deployServices(
 	ctx context.Context,
 	dockerCli command.Cli,
@@ -214,10 +215,12 @@ func deployServices(
 	}
 
 	for internalName, serviceSpec := range services {
-		name := namespace.Scope(internalName)
+		var (
+			name        = namespace.Scope(internalName)
+			image       = serviceSpec.TaskTemplate.ContainerSpec.Image
+			encodedAuth string
+		)
 
-		encodedAuth := ""
-		image := serviceSpec.TaskTemplate.ContainerSpec.Image
 		if sendAuth {
 			// Retrieve encoded auth token from the image reference
 			encodedAuth, err = command.RetrieveAuthTokenFromImage(ctx, dockerCli, image)
@@ -231,20 +234,33 @@ func deployServices(
 
 			updateOpts := types.ServiceUpdateOptions{EncodedRegistryAuth: encodedAuth}
 
-			switch {
+			switch resolveImage {
-			case resolveImage == ResolveImageAlways || (resolveImage == ResolveImageChanged && image != service.Spec.Labels[convert.LabelImage]):
+			case ResolveImageAlways:
 				// image should be updated by the server using QueryRegistry
 				updateOpts.QueryRegistry = true
-			case image == service.Spec.Labels[convert.LabelImage]:
+			case ResolveImageChanged:
+				if image != service.Spec.Labels[convert.LabelImage] {
+					// Query the registry to resolve digest for the updated image
+					updateOpts.QueryRegistry = true
+				} else {
 					// image has not changed; update the serviceSpec with the
 					// existing information that was set by QueryRegistry on the
 					// previous deploy. Otherwise this will trigger an incorrect
 					// service update.
 					serviceSpec.TaskTemplate.ContainerSpec.Image = service.Spec.TaskTemplate.ContainerSpec.Image
 				}
+			default:
+				if image == service.Spec.Labels[convert.LabelImage] {
+					// image has not changed; update the serviceSpec with the
+					// existing information that was set by QueryRegistry on the
+					// previous deploy. Otherwise this will trigger an incorrect
+					// service update.
+					serviceSpec.TaskTemplate.ContainerSpec.Image = service.Spec.TaskTemplate.ContainerSpec.Image
+				}
+			}
 
-			// Stack deploy does not have a `--force` option. Preserve existing ForceUpdate
+			// Stack deploy does not have a `--force` option. Preserve existing
-			// value so that tasks are not re-deployed if not updated.
+			// ForceUpdate value so that tasks are not re-deployed if not updated.
 			// TODO move this to API client?
 			serviceSpec.TaskTemplate.ForceUpdate = service.Spec.TaskTemplate.ForceUpdate