registry: basic merge of existing registry with generated registry config

pkg/client/cluster.go

@@ -188,6 +188,8 @@ func ClusterPrep(ctx context.Context, runtime k3drt.Runtime, clusterConfig *conf
 		if err != nil {
 			return fmt.Errorf("Failed to generate registry config file for k3s: %+v", err)
 		}
+		RegistryMergeConfig(ctx, regConf, clusterConfig.ClusterCreateOpts.Registries.Config)
+		log.Tracef("Merged registry config: %+v", regConf)
 		regConfBytes, err := yaml.Marshal(&regConf)
 		if err != nil {
 			return fmt.Errorf("Failed to marshal registry configuration: %+v", err)

pkg/client/registry.go

@@ -26,6 +26,7 @@ import (
 	"fmt"
 
 	"github.com/docker/go-connections/nat"
+	"github.com/imdario/mergo"
 	"github.com/rancher/k3d/v4/pkg/runtimes"
 	k3d "github.com/rancher/k3d/v4/pkg/types"
 	"github.com/rancher/k3d/v4/pkg/types/k3s"
@@ -305,3 +306,11 @@ func RegistryGenerateLocalRegistryHostingConfigMapYAML(ctx context.Context, regi
 
 	return cmYaml, nil
 }
+
+// RegistryMergeConfig merges a source registry config into an existing dest registry cofnig
+func RegistryMergeConfig(ctx context.Context, dest, src *k3s.Registry) error {
+	if err := mergo.MergeWithOverwrite(dest, src); err != nil {
+		return fmt.Errorf("Failed to merge registry configs: %+v", err)
+	}
+	return nil
+}

tests/assets/test_registries.yaml

@@ -0,0 +1,4 @@
+mirrors:
+  "my.company.registry":
+    endpoint:
+      - http://my.company.registry:5000