Disallow the use of legacy addons

Author: hakman

addons/README.md

@@ -1,3 +1,5 @@
 ## Addons
 
-Read on [addons](../docs/addons.md)
+**Legacy addons are deprecated and unmaintained!!!**
+
+Use [managed addons](../docs/addons.md) instead.

channels/pkg/cmd/apply_channel.go

@@ -88,13 +88,11 @@ func RunApplyChannel(ctx context.Context, f Factory, out io.Writer, options *App
 			// We recognize the following "well-known" format:
 			// <name> with no slashes ->
 			if strings.Contains(name, "/") {
-				return fmt.Errorf("Channel format not recognized (did you mean to use `-f` to specify a local file?): %q", name)
-			}
-			expanded := "https://raw.githubusercontent.com/kubernetes/kops/master/addons/" + name + "/addon.yaml"
-			location, err = url.Parse(expanded)
-			if err != nil {
-				return fmt.Errorf("unable to parse expanded argument %q as url", expanded)
+				return fmt.Errorf("channel format not recognized (did you mean to use `-f` to specify a local file?): %q", name)
 			}
+			// Disallow the use of legacy addons from the "well-known" location:
+			// https://raw.githubusercontent.com/kubernetes/kops/master/addons/<name>/addon.yaml
+			return fmt.Errorf("legacy addons are deprecated and unmaintained, use managed addons instead")
 		}
 		o, err := channels.LoadAddons(name, location)
 		if err != nil {