From 7ab8fde4940c3f7c2a5363675f5fe3c7c4cee859 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Max=20Sch=C3=A4fer?=
 <40192999+MaxSchaefer@users.noreply.github.com>
Date: Mon, 26 Jun 2023 01:36:26 +0200
Subject: [PATCH] feat(nameresolution/kubernetes): add ability for templating
 the dns name resolution (#2883)
MIME-Version: 1.0
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Content-Transfer-Encoding: 8bit

Signed-off-by: Max Schäfer <max-schaefer-lg@gmx.de>
Co-authored-by: Yaron Schneider <schneider.yaron@live.com>
Co-authored-by: Alessandro (Ale) Segala <43508+ItalyPaleAle@users.noreply.github.com>
---
 nameresolution/kubernetes/kubernetes.go      | 35 ++++++++++++++++--
 nameresolution/kubernetes/kubernetes_test.go | 39 ++++++++++++++++++++
 2 files changed, 70 insertions(+), 4 deletions(-)

diff --git a/nameresolution/kubernetes/kubernetes.go b/nameresolution/kubernetes/kubernetes.go
index a91e6f0deb..1741a7c90a 100644
--- a/nameresolution/kubernetes/kubernetes.go
+++ b/nameresolution/kubernetes/kubernetes.go
@@ -14,7 +14,9 @@ limitations under the License.
 package kubernetes
 
 import (
+	"bytes"
 	"strconv"
+	"text/template"
 
 	"github.com/dapr/components-contrib/nameresolution"
 	"github.com/dapr/kit/config"
@@ -24,11 +26,21 @@ import (
 const (
 	DefaultClusterDomain = "cluster.local"
 	ClusterDomainKey     = "clusterDomain"
+	TemplateKey          = "template"
 )
 
+func executeTemplateWithResolveRequest(tmpl *template.Template, req nameresolution.ResolveRequest) (string, error) {
+	var addr bytes.Buffer
+	if err := tmpl.Execute(&addr, req); err != nil {
+		return "", err
+	}
+	return addr.String(), nil
+}
+
 type resolver struct {
 	logger        logger.Logger
 	clusterDomain string
+	tmpl          *template.Template
 }
 
 // NewResolver creates Kubernetes name resolver.
@@ -36,6 +48,7 @@ func NewResolver(logger logger.Logger) nameresolution.Resolver {
 	return &resolver{
 		logger:        logger,
 		clusterDomain: DefaultClusterDomain,
+		tmpl:          nil,
 	}
 }
 
@@ -45,14 +58,25 @@ func (k *resolver) Init(metadata nameresolution.Metadata) error {
 	if err != nil {
 		return err
 	}
-	if config, ok := configInterface.(map[string]interface{}); ok {
-		clusterDomainPtr := config[ClusterDomainKey]
-		if clusterDomainPtr != nil {
-			clusterDomain, _ := clusterDomainPtr.(string)
+
+	if cfg, ok := configInterface.(map[string]interface{}); ok {
+		clusterDomainAny := cfg[ClusterDomainKey]
+		tmplStrAny := cfg[TemplateKey]
+
+		if clusterDomainAny != nil {
+			clusterDomain, _ := clusterDomainAny.(string)
 			if clusterDomain != "" {
 				k.clusterDomain = clusterDomain
 			}
 		}
+
+		if tmplStrAny != nil {
+			tmplStr, _ := tmplStrAny.(string)
+			if tmplStr != "" {
+				k.tmpl = template.Must(template.New("kubernetes-template").Parse(tmplStr))
+				k.logger.Debugf("using custom template %s", tmplStr)
+			}
+		}
 	}
 
 	return nil
@@ -60,6 +84,9 @@ func (k *resolver) Init(metadata nameresolution.Metadata) error {
 
 // ResolveID resolves name to address in Kubernetes.
 func (k *resolver) ResolveID(req nameresolution.ResolveRequest) (string, error) {
+	if k.tmpl != nil {
+		return executeTemplateWithResolveRequest(k.tmpl, req)
+	}
 	// Dapr requires this formatting for Kubernetes services
 	return req.ID + "-dapr." + req.Namespace + ".svc." + k.clusterDomain + ":" + strconv.Itoa(req.Port), nil
 }
diff --git a/nameresolution/kubernetes/kubernetes_test.go b/nameresolution/kubernetes/kubernetes_test.go
index d450b5bebe..3028de6c69 100644
--- a/nameresolution/kubernetes/kubernetes_test.go
+++ b/nameresolution/kubernetes/kubernetes_test.go
@@ -48,3 +48,42 @@ func TestResolveWithCustomClusterDomain(t *testing.T) {
 	assert.NoError(t, err)
 	assert.Equal(t, expect, target)
 }
+
+func TestResolveWithTemplate(t *testing.T) {
+	resolver := NewResolver(logger.NewLogger("test"))
+	_ = resolver.Init(nameresolution.Metadata{
+		Configuration: map[string]interface{}{
+			"template": "{{.ID}}-{{.Namespace}}.internal:{{.Port}}",
+		},
+	})
+
+	request := nameresolution.ResolveRequest{ID: "myid", Namespace: "abc", Port: 1234}
+	const expected = "myid-abc.internal:1234"
+	target, err := resolver.ResolveID(request)
+
+	assert.NoError(t, err)
+	assert.Equal(t, target, expected)
+}
+
+func TestResolveWithTemplateAndData(t *testing.T) {
+	resolver := NewResolver(logger.NewLogger("test"))
+	_ = resolver.Init(nameresolution.Metadata{
+		Configuration: map[string]interface{}{
+			"template": "{{.ID}}-{{.Data.region}}.internal:{{.Port}}",
+		},
+	})
+
+	request := nameresolution.ResolveRequest{
+		ID:        "myid",
+		Namespace: "abc",
+		Port:      1234,
+		Data: map[string]string{
+			"region": "myland",
+		},
+	}
+	const expected = "myid-myland.internal:1234"
+	target, err := resolver.ResolveID(request)
+
+	assert.NoError(t, err)
+	assert.Equal(t, target, expected)
+}