feat(cli): add Cobra binder and backend switch (#5820)

TobyTheHutt · web-flow · commit f80f7e0666cb · 2025-09-09T02:57:39.000-07:00
* add FlagBinder with Kingpin and Cobra implementations * support --cli-backend and EXTERNAL_DNS_CLI (default: kingpin) * add tests for binders and CLI switch Refs: #5379 Signed-off-by: Tobias Harnickell <tobias.harnickell@bedag.ch>
diff --git a/pkg/apis/externaldns/binders.go b/pkg/apis/externaldns/binders.go
@@ -0,0 +1,121 @@
+/*
+Copyright 2025 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package externaldns
+
+import (
+	"strconv"
+	"time"
+
+	"github.com/alecthomas/kingpin/v2"
+	"github.com/spf13/cobra"
+)
+
+// FlagBinder abstracts flag registration for different CLI backends.
+type FlagBinder interface {
+	StringVar(name, help, def string, target *string)
+	BoolVar(name, help string, def bool, target *bool)
+	DurationVar(name, help string, def time.Duration, target *time.Duration)
+	IntVar(name, help string, def int, target *int)
+	Int64Var(name, help string, def int64, target *int64)
+	StringsVar(name, help string, def []string, target *[]string)
+	EnumVar(name, help, def string, target *string, allowed ...string)
+}
+
+// KingpinBinder implements FlagBinder using github.com/alecthomas/kingpin/v2.
+type KingpinBinder struct {
+	App *kingpin.Application
+}
+
+// NewKingpinBinder creates a FlagBinder backed by a kingpin Application.
+func NewKingpinBinder(app *kingpin.Application) *KingpinBinder {
+	return &KingpinBinder{App: app}
+}
+
+func (b *KingpinBinder) StringVar(name, help, def string, target *string) {
+	b.App.Flag(name, help).Default(def).StringVar(target)
+}
+
+func (b *KingpinBinder) BoolVar(name, help string, def bool, target *bool) {
+	if def {
+		b.App.Flag(name, help).Default("true").BoolVar(target)
+	} else {
+		b.App.Flag(name, help).Default("false").BoolVar(target)
+	}
+}
+
+func (b *KingpinBinder) DurationVar(name, help string, def time.Duration, target *time.Duration) {
+	b.App.Flag(name, help).Default(def.String()).DurationVar(target)
+}
+
+func (b *KingpinBinder) IntVar(name, help string, def int, target *int) {
+	b.App.Flag(name, help).Default(strconv.Itoa(def)).IntVar(target)
+}
+
+func (b *KingpinBinder) Int64Var(name, help string, def int64, target *int64) {
+	b.App.Flag(name, help).Default(strconv.FormatInt(def, 10)).Int64Var(target)
+}
+
+func (b *KingpinBinder) StringsVar(name, help string, def []string, target *[]string) {
+	if len(def) > 0 {
+		b.App.Flag(name, help).Default(def...).StringsVar(target)
+		return
+	}
+	b.App.Flag(name, help).StringsVar(target)
+}
+
+func (b *KingpinBinder) EnumVar(name, help, def string, target *string, allowed ...string) {
+	b.App.Flag(name, help).Default(def).EnumVar(target, allowed...)
+}
+
+// CobraBinder implements FlagBinder using github.com/spf13/cobra.
+type CobraBinder struct {
+	Cmd *cobra.Command
+}
+
+// NewCobraBinder creates a FlagBinder backed by a Cobra command.
+func NewCobraBinder(cmd *cobra.Command) *CobraBinder {
+	return &CobraBinder{Cmd: cmd}
+}
+
+func (b *CobraBinder) StringVar(name, help, def string, target *string) {
+	b.Cmd.Flags().StringVar(target, name, def, help)
+}
+
+func (b *CobraBinder) BoolVar(name, help string, def bool, target *bool) {
+	b.Cmd.Flags().BoolVar(target, name, def, help)
+}
+
+func (b *CobraBinder) DurationVar(name, help string, def time.Duration, target *time.Duration) {
+	b.Cmd.Flags().DurationVar(target, name, def, help)
+}
+
+func (b *CobraBinder) IntVar(name, help string, def int, target *int) {
+	b.Cmd.Flags().IntVar(target, name, def, help)
+}
+
+func (b *CobraBinder) Int64Var(name, help string, def int64, target *int64) {
+	b.Cmd.Flags().Int64Var(target, name, def, help)
+}
+
+func (b *CobraBinder) StringsVar(name, help string, def []string, target *[]string) {
+	// Preserve repeatable flag semantics.
+	b.Cmd.Flags().StringArrayVar(target, name, def, help)
+}
+
+func (b *CobraBinder) EnumVar(name, help, def string, target *string, allowed ...string) {
+	b.Cmd.Flags().StringVar(target, name, def, help)
+}
diff --git a/pkg/apis/externaldns/binders_test.go b/pkg/apis/externaldns/binders_test.go
@@ -0,0 +1,139 @@
+/*
+Copyright 2025 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package externaldns
+
+import (
+	"testing"
+	"time"
+
+	"github.com/alecthomas/kingpin/v2"
+	"github.com/spf13/cobra"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestKingpinBinderParsesAllTypes(t *testing.T) {
+	app := kingpin.New("test", "")
+	b := NewKingpinBinder(app)
+
+	var (
+		s    string
+		bval bool
+		d    time.Duration
+		i    int
+		i64  int64
+		ss   []string
+		e    string
+	)
+
+	b.StringVar("s", "string flag", "def", &s)
+	b.BoolVar("b", "bool flag", true, &bval)
+	b.DurationVar("d", "duration flag", 5*time.Second, &d)
+	b.IntVar("i", "int flag", 7, &i)
+	b.Int64Var("i64", "int64 flag", 9, &i64)
+	b.StringsVar("ss", "strings flag", []string{"x"}, &ss)
+	b.EnumVar("e", "enum flag", "a", &e, "a", "b")
+
+	_, err := app.Parse([]string{"--s=abc", "--no-b", "--d=2s", "--i=42", "--i64=64", "--ss=one", "--ss=two", "--e=b"})
+	require.NoError(t, err)
+
+	assert.Equal(t, "abc", s)
+	assert.False(t, bval)
+	assert.Equal(t, 2*time.Second, d)
+	assert.Equal(t, 42, i)
+	assert.Equal(t, int64(64), i64)
+	assert.ElementsMatch(t, []string{"one", "two"}, ss)
+	assert.Equal(t, "b", e)
+}
+
+func TestKingpinBinderEnumValidation(t *testing.T) {
+	app := kingpin.New("test", "")
+	b := NewKingpinBinder(app)
+
+	var e string
+	b.EnumVar("e", "enum flag", "a", &e, "a", "b")
+
+	_, err := app.Parse([]string{"--e=c"})
+	require.Error(t, err)
+}
+
+func TestKingpinBinderStringsVarNoDefaultAndBoolDefaultFalse(t *testing.T) {
+	app := kingpin.New("test", "")
+	b := NewKingpinBinder(app)
+
+	var (
+		ss []string
+		b2 bool
+	)
+
+	b.StringsVar("ss", "strings flag", nil, &ss)
+	b.BoolVar("b2", "bool2 flag", false, &b2)
+
+	_, err := app.Parse([]string{})
+	require.NoError(t, err)
+
+	assert.Empty(t, ss)
+	assert.False(t, b2)
+}
+
+func TestCobraBinderParsesAllTypes(t *testing.T) {
+	cmd := &cobra.Command{Use: "test"}
+	b := NewCobraBinder(cmd)
+
+	var (
+		s    string
+		bval bool
+		d    time.Duration
+		i    int
+		i64  int64
+		ss   []string
+		e    string
+	)
+
+	b.StringVar("s", "string flag", "def", &s)
+	b.BoolVar("b", "bool flag", true, &bval)
+	b.DurationVar("d", "duration flag", 5*time.Second, &d)
+	b.IntVar("i", "int flag", 7, &i)
+	b.Int64Var("i64", "int64 flag", 9, &i64)
+	b.StringsVar("ss", "strings flag", []string{"x"}, &ss)
+	b.EnumVar("e", "enum flag", "a", &e, "a", "b")
+
+	cmd.SetArgs([]string{"--s=abc", "--b=false", "--d=2s", "--i=42", "--i64=64", "--ss=one", "--ss=two", "--e=b"})
+	err := cmd.Execute()
+	require.NoError(t, err)
+
+	assert.Equal(t, "abc", s)
+	assert.False(t, bval)
+	assert.Equal(t, 2*time.Second, d)
+	assert.Equal(t, 42, i)
+	assert.Equal(t, int64(64), i64)
+	assert.ElementsMatch(t, []string{"one", "two"}, ss)
+	assert.Equal(t, "b", e)
+}
+
+func TestCobraBinderEnumNotValidatedHere(t *testing.T) {
+	cmd := &cobra.Command{Use: "test"}
+	b := NewCobraBinder(cmd)
+
+	var e string
+	b.EnumVar("e", "enum flag", "a", &e, "a", "b")
+
+	cmd.SetArgs([]string{"--e=c"})
+	err := cmd.Execute()
+	require.NoError(t, err)
+	assert.Equal(t, "c", e)
+}
diff --git a/pkg/apis/externaldns/types.go b/pkg/apis/externaldns/types.go
@@ -18,6 +18,7 @@ package externaldns
 
 import (
 	"fmt"
+	"os"
 	"reflect"
 	"regexp"
 	"strconv"
@@ -30,6 +31,7 @@ import (
 
 	"github.com/alecthomas/kingpin/v2"
 	"github.com/sirupsen/logrus"
+	"github.com/spf13/cobra"
 )
 
 const (
@@ -421,16 +423,80 @@ func allLogLevelsAsStrings() []string {
 
 // ParseFlags adds and parses flags from command line
 func (cfg *Config) ParseFlags(args []string) error {
-	app := App(cfg)
+	backend := ""
+	pruned := make([]string, 0, len(args))
+	skipNext := false
+	for i := 0; i < len(args); i++ {
+		if skipNext {
+			skipNext = false
+			continue
+		}
+		a := args[i]
+		if strings.HasPrefix(a, "--cli-backend") {
+			val := ""
+			if a == "--cli-backend" {
+				if i+1 < len(args) {
+					val = args[i+1]
+					skipNext = true
+				}
+			} else if strings.HasPrefix(a, "--cli-backend=") {
+				val = strings.TrimPrefix(a, "--cli-backend=")
+			}
+			if val != "" {
+				backend = val
+			}
+			continue
+		}
+		pruned = append(pruned, a)
+	}
+	if backend == "" {
+		backend = os.Getenv("EXTERNAL_DNS_CLI")
+	}
+	if strings.EqualFold(backend, "cobra") {
+		cmd := newCobraCommand(cfg)
+		cmd.SetArgs(pruned)
+		if err := cmd.Execute(); err != nil {
+			return err
+		}
+		return nil
+	}
 
-	_, err := app.Parse(args)
+	app := App(cfg)
+	_, err := app.Parse(pruned)
 	if err != nil {
 		return err
 	}
 
 	return nil
 }
 
+func newCobraCommand(cfg *Config) *cobra.Command {
+	cmd := &cobra.Command{
+		Use:           "external-dns",
+		Short:         "ExternalDNS synchronizes exposed Kubernetes Services and Ingresses with DNS providers.",
+		SilenceUsage:  true,
+		SilenceErrors: true,
+		RunE: func(cmd *cobra.Command, args []string) error {
+			return nil
+		},
+	}
+
+	b := NewCobraBinder(cmd)
+
+	b.EnumVar("provider", "The DNS provider where the DNS records will be created.", defaultConfig.Provider, &cfg.Provider)
+	b.StringsVar("source", "The resource types that are queried for endpoints; specify multiple times for multiple sources.", cfg.Sources, &cfg.Sources)
+
+	b.StringVar("server", "The Kubernetes API server to connect to (default: auto-detect)", defaultConfig.APIServerURL, &cfg.APIServerURL)
+	b.StringVar("kubeconfig", "Retrieve target cluster configuration from a Kubernetes configuration file (default: auto-detect)", defaultConfig.KubeConfig, &cfg.KubeConfig)
+	b.DurationVar("request-timeout", "Request timeout when calling Kubernetes APIs. 0s means no timeout", defaultConfig.RequestTimeout, &cfg.RequestTimeout)
+
+	b.StringVar("namespace", "Limit resources queried for endpoints to a specific namespace (default: all namespaces)", defaultConfig.Namespace, &cfg.Namespace)
+	b.StringsVar("domain-filter", "Limit possible target zones by domain suffix (optional)", defaultConfig.DomainFilter, &cfg.DomainFilter)
+	b.StringVar("openshift-router-name", "if source is openshift-route then you can pass the ingress controller name.", cfg.OCPRouterName, &cfg.OCPRouterName)
+
+	return cmd
+}
+
 func (cfg *Config) AddSourceWrapper(name string) {
 	if cfg.sourceWrappers == nil {
 		cfg.sourceWrappers = make(map[string]bool)
diff --git a/pkg/apis/externaldns/types_test.go b/pkg/apis/externaldns/types_test.go
