k3s/pkg/kubelet/network/dns/dns_test.go

/*
Copyright 2017 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 dns

import (
	"fmt"
	"io/ioutil"
	"net"
	"os"
	"strings"
	"testing"

	"k8s.io/api/core/v1"
	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
	"k8s.io/apimachinery/pkg/types"
	"k8s.io/apimachinery/pkg/util/sets"
	utilfeature "k8s.io/apiserver/pkg/util/feature"
	"k8s.io/client-go/tools/record"
	runtimeapi "k8s.io/kubernetes/pkg/kubelet/apis/cri/runtime/v1alpha2"

	"github.com/stretchr/testify/assert"
	"github.com/stretchr/testify/require"
)

var (
	fetchEvent = func(recorder *record.FakeRecorder) string {
		select {
		case event := <-recorder.Events:
			return event
		default:
			return ""
		}
	}
)

func TestParseResolvConf(t *testing.T) {
	testCases := []struct {
		data        string
		nameservers []string
		searches    []string
		options     []string
	}{
		{"", []string{}, []string{}, []string{}},
		{" ", []string{}, []string{}, []string{}},
		{"\n", []string{}, []string{}, []string{}},
		{"\t\n\t", []string{}, []string{}, []string{}},
		{"#comment\n", []string{}, []string{}, []string{}},
		{" #comment\n", []string{}, []string{}, []string{}},
		{"#comment\n#comment", []string{}, []string{}, []string{}},
		{"#comment\nnameserver", []string{}, []string{}, []string{}},
		{"#comment\nnameserver\nsearch", []string{}, []string{}, []string{}},
		{"nameserver 1.2.3.4", []string{"1.2.3.4"}, []string{}, []string{}},
		{" nameserver 1.2.3.4", []string{"1.2.3.4"}, []string{}, []string{}},
		{"\tnameserver 1.2.3.4", []string{"1.2.3.4"}, []string{}, []string{}},
		{"nameserver\t1.2.3.4", []string{"1.2.3.4"}, []string{}, []string{}},
		{"nameserver \t 1.2.3.4", []string{"1.2.3.4"}, []string{}, []string{}},
		{"nameserver 1.2.3.4\nnameserver 5.6.7.8", []string{"1.2.3.4", "5.6.7.8"}, []string{}, []string{}},
		{"nameserver 1.2.3.4 #comment", []string{"1.2.3.4"}, []string{}, []string{}},
		{"search foo", []string{}, []string{"foo"}, []string{}},
		{"search foo bar", []string{}, []string{"foo", "bar"}, []string{}},
		{"search foo bar bat\n", []string{}, []string{"foo", "bar", "bat"}, []string{}},
		{"search foo\nsearch bar", []string{}, []string{"bar"}, []string{}},
		{"nameserver 1.2.3.4\nsearch foo bar", []string{"1.2.3.4"}, []string{"foo", "bar"}, []string{}},
		{"nameserver 1.2.3.4\nsearch foo\nnameserver 5.6.7.8\nsearch bar", []string{"1.2.3.4", "5.6.7.8"}, []string{"bar"}, []string{}},
		{"#comment\nnameserver 1.2.3.4\n#comment\nsearch foo\ncomment", []string{"1.2.3.4"}, []string{"foo"}, []string{}},
		{"options ndots:5 attempts:2", []string{}, []string{}, []string{"ndots:5", "attempts:2"}},
		{"options ndots:1\noptions ndots:5 attempts:3", []string{}, []string{}, []string{"ndots:5", "attempts:3"}},
		{"nameserver 1.2.3.4\nsearch foo\nnameserver 5.6.7.8\nsearch bar\noptions ndots:5 attempts:4", []string{"1.2.3.4", "5.6.7.8"}, []string{"bar"}, []string{"ndots:5", "attempts:4"}},
	}
	for i, tc := range testCases {
		ns, srch, opts, err := parseResolvConf(strings.NewReader(tc.data))
		require.NoError(t, err)
		assert.EqualValues(t, tc.nameservers, ns, "test case [%d]: name servers", i)
		assert.EqualValues(t, tc.searches, srch, "test case [%d] searches", i)
		assert.EqualValues(t, tc.options, opts, "test case [%d] options", i)
	}
}

func TestFormDNSSearchFitsLimits(t *testing.T) {
	recorder := record.NewFakeRecorder(20)
	nodeRef := &v1.ObjectReference{
		Kind:      "Node",
		Name:      string("testNode"),
		UID:       types.UID("testNode"),
		Namespace: "",
	}
	testClusterDNSDomain := "TEST"

	configurer := NewConfigurer(recorder, nodeRef, nil, nil, testClusterDNSDomain, "")

	pod := &v1.Pod{
		ObjectMeta: metav1.ObjectMeta{
			UID:         "",
			Name:        "test_pod",
			Namespace:   "testNS",
			Annotations: map[string]string{},
		},
	}

	testCases := []struct {
		hostNames    []string
		resultSearch []string
		events       []string
	}{
		{
			[]string{"testNS.svc.TEST", "svc.TEST", "TEST"},
			[]string{"testNS.svc.TEST", "svc.TEST", "TEST"},
			[]string{},
		},

		{
			[]string{"testNS.svc.TEST", "svc.TEST", "TEST", "AAA", "BBB"},
			[]string{"testNS.svc.TEST", "svc.TEST", "TEST", "AAA", "BBB"},
			[]string{},
		},

		{
			[]string{"testNS.svc.TEST", "svc.TEST", "TEST", "AAA", strings.Repeat("B", 256), "BBB"},
			[]string{"testNS.svc.TEST", "svc.TEST", "TEST", "AAA"},
			[]string{"Search Line limits were exceeded, some search paths have been omitted, the applied search line is: testNS.svc.TEST svc.TEST TEST AAA"},
		},

		{
			[]string{"testNS.svc.TEST", "svc.TEST", "TEST", "AAA", "BBB", "CCC", "DDD"},
			[]string{"testNS.svc.TEST", "svc.TEST", "TEST", "AAA", "BBB", "CCC"},
			[]string{"Search Line limits were exceeded, some search paths have been omitted, the applied search line is: testNS.svc.TEST svc.TEST TEST AAA BBB CCC"},
		},
	}

	for i, tc := range testCases {
		dnsSearch := configurer.formDNSSearchFitsLimits(tc.hostNames, pod)
		assert.EqualValues(t, tc.resultSearch, dnsSearch, "test [%d]", i)
		for _, expectedEvent := range tc.events {
			expected := fmt.Sprintf("%s %s %s", v1.EventTypeWarning, "DNSConfigForming", expectedEvent)
			event := fetchEvent(recorder)
			assert.Equal(t, expected, event, "test [%d]", i)
		}
	}
}

func TestFormDNSNameserversFitsLimits(t *testing.T) {
	recorder := record.NewFakeRecorder(20)
	nodeRef := &v1.ObjectReference{
		Kind:      "Node",
		Name:      string("testNode"),
		UID:       types.UID("testNode"),
		Namespace: "",
	}
	testClusterDNSDomain := "TEST"

	configurer := NewConfigurer(recorder, nodeRef, nil, nil, testClusterDNSDomain, "")

	pod := &v1.Pod{
		ObjectMeta: metav1.ObjectMeta{
			UID:         "",
			Name:        "test_pod",
			Namespace:   "testNS",
			Annotations: map[string]string{},
		},
	}

	testCases := []struct {
		desc               string
		nameservers        []string
		expectedNameserver []string
		expectedEvent      bool
	}{
		{
			desc:               "valid: 1 nameserver",
			nameservers:        []string{"127.0.0.1"},
			expectedNameserver: []string{"127.0.0.1"},
			expectedEvent:      false,
		},
		{
			desc:               "valid: 3 nameservers",
			nameservers:        []string{"127.0.0.1", "10.0.0.10", "8.8.8.8"},
			expectedNameserver: []string{"127.0.0.1", "10.0.0.10", "8.8.8.8"},
			expectedEvent:      false,
		},
		{
			desc:               "invalid: 4 nameservers, trimmed to 3",
			nameservers:        []string{"127.0.0.1", "10.0.0.10", "8.8.8.8", "1.2.3.4"},
			expectedNameserver: []string{"127.0.0.1", "10.0.0.10", "8.8.8.8"},
			expectedEvent:      true,
		},
	}

	for _, tc := range testCases {
		appliedNameservers := configurer.formDNSNameserversFitsLimits(tc.nameservers, pod)
		assert.EqualValues(t, tc.expectedNameserver, appliedNameservers, tc.desc)
		event := fetchEvent(recorder)
		if tc.expectedEvent && len(event) == 0 {
			t.Errorf("%s: formDNSNameserversFitsLimits(%v) expected event, got no event.", tc.desc, tc.nameservers)
		} else if !tc.expectedEvent && len(event) > 0 {
			t.Errorf("%s: formDNSNameserversFitsLimits(%v) expected no event, got event: %v", tc.desc, tc.nameservers, event)
		}
	}
}

func TestMergeDNSOptions(t *testing.T) {
	testOptionValue := "3"

	testCases := []struct {
		desc                     string
		existingDNSConfigOptions []string
		dnsConfigOptions         []v1.PodDNSConfigOption
		expectedOptions          []string
	}{
		{
			desc: "Empty dnsConfigOptions",
			existingDNSConfigOptions: []string{"ndots:5", "debug"},
			dnsConfigOptions:         nil,
			expectedOptions:          []string{"ndots:5", "debug"},
		},
		{
			desc: "No duplicated entries",
			existingDNSConfigOptions: []string{"ndots:5", "debug"},
			dnsConfigOptions: []v1.PodDNSConfigOption{
				{Name: "single-request"},
				{Name: "attempts", Value: &testOptionValue},
			},
			expectedOptions: []string{"ndots:5", "debug", "single-request", "attempts:3"},
		},
		{
			desc: "Overwrite duplicated entries",
			existingDNSConfigOptions: []string{"ndots:5", "debug"},
			dnsConfigOptions: []v1.PodDNSConfigOption{
				{Name: "ndots", Value: &testOptionValue},
				{Name: "debug"},
				{Name: "single-request"},
				{Name: "attempts", Value: &testOptionValue},
			},
			expectedOptions: []string{"ndots:3", "debug", "single-request", "attempts:3"},
		},
	}

	for _, tc := range testCases {
		options := mergeDNSOptions(tc.existingDNSConfigOptions, tc.dnsConfigOptions)
		// Options order may be changed after conversion.
		if !sets.NewString(options...).Equal(sets.NewString(tc.expectedOptions...)) {
			t.Errorf("%s: mergeDNSOptions(%v, %v)=%v, want %v", tc.desc, tc.existingDNSConfigOptions, tc.dnsConfigOptions, options, tc.expectedOptions)
		}
	}
}

func TestGetPodDNSType(t *testing.T) {
	customDNSEnabled := utilfeature.DefaultFeatureGate.Enabled("CustomPodDNS")
	defer func() {
		// Restoring the old value.
		if err := utilfeature.DefaultFeatureGate.Set(fmt.Sprintf("CustomPodDNS=%v", customDNSEnabled)); err != nil {
			t.Errorf("Failed to set CustomPodDNS feature gate: %v", err)
		}
	}()

	recorder := record.NewFakeRecorder(20)
	nodeRef := &v1.ObjectReference{
		Kind:      "Node",
		Name:      string("testNode"),
		UID:       types.UID("testNode"),
		Namespace: "",
	}
	testClusterDNSDomain := "TEST"
	clusterNS := "203.0.113.1"
	testClusterDNS := []net.IP{net.ParseIP(clusterNS)}

	configurer := NewConfigurer(recorder, nodeRef, nil, nil, testClusterDNSDomain, "")

	pod := &v1.Pod{
		ObjectMeta: metav1.ObjectMeta{
			UID:         "",
			Name:        "test_pod",
			Namespace:   "testNS",
			Annotations: map[string]string{},
		},
	}

	testCases := []struct {
		desc                    string
		customPodDNSFeatureGate bool
		hasClusterDNS           bool
		hostNetwork             bool
		dnsPolicy               v1.DNSPolicy
		expectedDNSType         podDNSType
		expectedError           bool
	}{
		{
			desc:            "valid DNSClusterFirst without hostnetwork",
			hasClusterDNS:   true,
			dnsPolicy:       v1.DNSClusterFirst,
			expectedDNSType: podDNSCluster,
		},
		{
			desc:            "valid DNSClusterFirstWithHostNet with hostnetwork",
			hasClusterDNS:   true,
			hostNetwork:     true,
			dnsPolicy:       v1.DNSClusterFirstWithHostNet,
			expectedDNSType: podDNSCluster,
		},
		{
			desc:            "valid DNSClusterFirstWithHostNet without hostnetwork",
			hasClusterDNS:   true,
			dnsPolicy:       v1.DNSClusterFirstWithHostNet,
			expectedDNSType: podDNSCluster,
		},
		{
			desc:            "valid DNSDefault without hostnetwork",
			dnsPolicy:       v1.DNSDefault,
			expectedDNSType: podDNSHost,
		},
		{
			desc:            "valid DNSDefault with hostnetwork",
			hostNetwork:     true,
			dnsPolicy:       v1.DNSDefault,
			expectedDNSType: podDNSHost,
		},
		{
			desc:            "DNSClusterFirst with hostnetwork, fallback to DNSDefault",
			hasClusterDNS:   true,
			hostNetwork:     true,
			dnsPolicy:       v1.DNSClusterFirst,
			expectedDNSType: podDNSHost,
		},
		{
			desc: "valid DNSNone with feature gate",
			customPodDNSFeatureGate: true,
			dnsPolicy:               v1.DNSNone,
			expectedDNSType:         podDNSNone,
		},
		{
			desc:          "DNSNone without feature gate, should return error",
			dnsPolicy:     v1.DNSNone,
			expectedError: true,
		},
		{
			desc:          "invalid DNS policy, should return error",
			dnsPolicy:     "invalidPolicy",
			expectedError: true,
		},
	}

	for _, tc := range testCases {
		if err := utilfeature.DefaultFeatureGate.Set(fmt.Sprintf("CustomPodDNS=%v", tc.customPodDNSFeatureGate)); err != nil {
			t.Errorf("Failed to set CustomPodDNS feature gate: %v", err)
		}

		if tc.hasClusterDNS {
			configurer.clusterDNS = testClusterDNS
		} else {
			configurer.clusterDNS = nil
		}
		pod.Spec.DNSPolicy = tc.dnsPolicy
		pod.Spec.HostNetwork = tc.hostNetwork

		resType, err := getPodDNSType(pod)
		if tc.expectedError {
			if err == nil {
				t.Errorf("%s: GetPodDNSType(%v) got no error, want error", tc.desc, pod)
			}
			continue
		}
		if resType != tc.expectedDNSType {
			t.Errorf("%s: GetPodDNSType(%v)=%v, want %v", tc.desc, pod, resType, tc.expectedDNSType)
		}
	}
}

func TestGetPodDNS(t *testing.T) {
	recorder := record.NewFakeRecorder(20)
	nodeRef := &v1.ObjectReference{
		Kind:      "Node",
		Name:      string("testNode"),
		UID:       types.UID("testNode"),
		Namespace: "",
	}
	clusterNS := "203.0.113.1"
	testClusterDNSDomain := "kubernetes.io"
	testClusterDNS := []net.IP{net.ParseIP(clusterNS)}

	configurer := NewConfigurer(recorder, nodeRef, nil, testClusterDNS, testClusterDNSDomain, "")

	pods := newTestPods(4)
	pods[0].Spec.DNSPolicy = v1.DNSClusterFirstWithHostNet
	pods[1].Spec.DNSPolicy = v1.DNSClusterFirst
	pods[2].Spec.DNSPolicy = v1.DNSClusterFirst
	pods[2].Spec.HostNetwork = false
	pods[3].Spec.DNSPolicy = v1.DNSDefault

	options := make([]struct {
		DNS       []string
		DNSSearch []string
	}, 4)
	for i, pod := range pods {
		var err error
		dnsConfig, err := configurer.GetPodDNS(pod)
		if err != nil {
			t.Fatalf("failed to generate container options: %v", err)
		}
		options[i].DNS, options[i].DNSSearch = dnsConfig.Servers, dnsConfig.Searches
	}
	if len(options[0].DNS) != 1 || options[0].DNS[0] != clusterNS {
		t.Errorf("expected nameserver %s, got %+v", clusterNS, options[0].DNS)
	}
	if len(options[0].DNSSearch) == 0 || options[0].DNSSearch[0] != ".svc."+configurer.ClusterDomain {
		t.Errorf("expected search %s, got %+v", ".svc."+configurer.ClusterDomain, options[0].DNSSearch)
	}
	if len(options[1].DNS) != 1 || options[1].DNS[0] != "127.0.0.1" {
		t.Errorf("expected nameserver 127.0.0.1, got %+v", options[1].DNS)
	}
	if len(options[1].DNSSearch) != 1 || options[1].DNSSearch[0] != "." {
		t.Errorf("expected search \".\", got %+v", options[1].DNSSearch)
	}
	if len(options[2].DNS) != 1 || options[2].DNS[0] != clusterNS {
		t.Errorf("expected nameserver %s, got %+v", clusterNS, options[2].DNS)
	}
	if len(options[2].DNSSearch) == 0 || options[2].DNSSearch[0] != ".svc."+configurer.ClusterDomain {
		t.Errorf("expected search %s, got %+v", ".svc."+configurer.ClusterDomain, options[2].DNSSearch)
	}
	if len(options[3].DNS) != 1 || options[3].DNS[0] != "127.0.0.1" {
		t.Errorf("expected nameserver 127.0.0.1, got %+v", options[3].DNS)
	}
	if len(options[3].DNSSearch) != 1 || options[3].DNSSearch[0] != "." {
		t.Errorf("expected search \".\", got %+v", options[3].DNSSearch)
	}

	testResolverConfig := "/etc/resolv.conf"
	configurer = NewConfigurer(recorder, nodeRef, nil, testClusterDNS, testClusterDNSDomain, testResolverConfig)
	for i, pod := range pods {
		var err error
		dnsConfig, err := configurer.GetPodDNS(pod)
		if err != nil {
			t.Fatalf("failed to generate container options: %v", err)
		}
		options[i].DNS, options[i].DNSSearch = dnsConfig.Servers, dnsConfig.Searches
	}
	t.Logf("nameservers %+v", options[1].DNS)
	if len(options[0].DNS) != 1 {
		t.Errorf("expected cluster nameserver only, got %+v", options[0].DNS)
	} else if options[0].DNS[0] != clusterNS {
		t.Errorf("expected nameserver %s, got %v", clusterNS, options[0].DNS[0])
	}
	expLength := len(options[1].DNSSearch) + 3
	if expLength > 6 {
		expLength = 6
	}
	if len(options[0].DNSSearch) != expLength {
		t.Errorf("expected prepend of cluster domain, got %+v", options[0].DNSSearch)
	} else if options[0].DNSSearch[0] != ".svc."+configurer.ClusterDomain {
		t.Errorf("expected domain %s, got %s", ".svc."+configurer.ClusterDomain, options[0].DNSSearch)
	}
	if len(options[2].DNS) != 1 {
		t.Errorf("expected cluster nameserver only, got %+v", options[2].DNS)
	} else if options[2].DNS[0] != clusterNS {
		t.Errorf("expected nameserver %s, got %v", clusterNS, options[2].DNS[0])
	}
	if len(options[2].DNSSearch) != expLength {
		t.Errorf("expected prepend of cluster domain, got %+v", options[2].DNSSearch)
	} else if options[2].DNSSearch[0] != ".svc."+configurer.ClusterDomain {
		t.Errorf("expected domain %s, got %s", ".svc."+configurer.ClusterDomain, options[0].DNSSearch)
	}
}

func TestGetPodDNSCustom(t *testing.T) {
	customDNSEnabled := utilfeature.DefaultFeatureGate.Enabled("CustomPodDNS")
	defer func() {
		// Restoring the old value.
		if err := utilfeature.DefaultFeatureGate.Set(fmt.Sprintf("CustomPodDNS=%v", customDNSEnabled)); err != nil {
			t.Errorf("Failed to set CustomPodDNS feature gate: %v", err)
		}
	}()

	recorder := record.NewFakeRecorder(20)
	nodeRef := &v1.ObjectReference{
		Kind:      "Node",
		Name:      string("testNode"),
		UID:       types.UID("testNode"),
		Namespace: "",
	}

	testPodNamespace := "testNS"
	testClusterNameserver := "10.0.0.10"
	testClusterDNSDomain := "kubernetes.io"
	testSvcDomain := fmt.Sprintf("svc.%s", testClusterDNSDomain)
	testNsSvcDomain := fmt.Sprintf("%s.svc.%s", testPodNamespace, testClusterDNSDomain)
	testNdotsOptionValue := "3"
	testHostNameserver := "8.8.8.8"
	testHostDomain := "host.domain"

	testPod := &v1.Pod{
		ObjectMeta: metav1.ObjectMeta{
			Name:      "test_pod",
			Namespace: testPodNamespace,
		},
	}

	resolvConfContent := []byte(fmt.Sprintf("nameserver %s\nsearch %s\n", testHostNameserver, testHostDomain))
	tmpfile, err := ioutil.TempFile("", "tmpResolvConf")
	if err != nil {
		t.Fatal(err)
	}
	defer os.Remove(tmpfile.Name())
	if _, err := tmpfile.Write(resolvConfContent); err != nil {
		t.Fatal(err)
	}
	if err := tmpfile.Close(); err != nil {
		t.Fatal(err)
	}

	configurer := NewConfigurer(recorder, nodeRef, nil, []net.IP{net.ParseIP(testClusterNameserver)}, testClusterDNSDomain, tmpfile.Name())

	testCases := []struct {
		desc                    string
		customPodDNSFeatureGate bool
		hostnetwork             bool
		dnsPolicy               v1.DNSPolicy
		dnsConfig               *v1.PodDNSConfig
		expectedDNSConfig       *runtimeapi.DNSConfig
	}{
		{
			desc:      "feature gate is disabled, DNSNone should fallback to DNSClusterFirst",
			dnsPolicy: v1.DNSNone,
			expectedDNSConfig: &runtimeapi.DNSConfig{
				Servers:  []string{testClusterNameserver},
				Searches: []string{testNsSvcDomain, testSvcDomain, testClusterDNSDomain, testHostDomain},
				Options:  []string{"ndots:5"},
			},
		},
		{
			desc: "feature gate is enabled, DNSNone without DNSConfig should have empty DNS settings",
			customPodDNSFeatureGate: true,
			dnsPolicy:               v1.DNSNone,
			expectedDNSConfig:       &runtimeapi.DNSConfig{},
		},
		{
			desc: "feature gate is enabled, DNSNone with DNSConfig should have a merged DNS settings",
			customPodDNSFeatureGate: true,
			dnsPolicy:               v1.DNSNone,
			dnsConfig: &v1.PodDNSConfig{
				Nameservers: []string{"203.0.113.1"},
				Searches:    []string{"my.domain", "second.domain"},
				Options: []v1.PodDNSConfigOption{
					{Name: "ndots", Value: &testNdotsOptionValue},
					{Name: "debug"},
				},
			},
			expectedDNSConfig: &runtimeapi.DNSConfig{
				Servers:  []string{"203.0.113.1"},
				Searches: []string{"my.domain", "second.domain"},
				Options:  []string{"ndots:3", "debug"},
			},
		},
		{
			desc: "feature gate is enabled, DNSClusterFirst with DNSConfig should have a merged DNS settings",
			customPodDNSFeatureGate: true,
			dnsPolicy:               v1.DNSClusterFirst,
			dnsConfig: &v1.PodDNSConfig{
				Nameservers: []string{"10.0.0.11"},
				Searches:    []string{"my.domain"},
				Options: []v1.PodDNSConfigOption{
					{Name: "ndots", Value: &testNdotsOptionValue},
					{Name: "debug"},
				},
			},
			expectedDNSConfig: &runtimeapi.DNSConfig{
				Servers:  []string{testClusterNameserver, "10.0.0.11"},
				Searches: []string{testNsSvcDomain, testSvcDomain, testClusterDNSDomain, testHostDomain, "my.domain"},
				Options:  []string{"ndots:3", "debug"},
			},
		},
		{
			desc: "feature gate is enabled, DNSClusterFirstWithHostNet with DNSConfig should have a merged DNS settings",
			customPodDNSFeatureGate: true,
			hostnetwork:             true,
			dnsPolicy:               v1.DNSClusterFirstWithHostNet,
			dnsConfig: &v1.PodDNSConfig{
				Nameservers: []string{"10.0.0.11"},
				Searches:    []string{"my.domain"},
				Options: []v1.PodDNSConfigOption{
					{Name: "ndots", Value: &testNdotsOptionValue},
					{Name: "debug"},
				},
			},
			expectedDNSConfig: &runtimeapi.DNSConfig{
				Servers:  []string{testClusterNameserver, "10.0.0.11"},
				Searches: []string{testNsSvcDomain, testSvcDomain, testClusterDNSDomain, testHostDomain, "my.domain"},
				Options:  []string{"ndots:3", "debug"},
			},
		},
		{
			desc: "feature gate is enabled, DNSDefault with DNSConfig should have a merged DNS settings",
			customPodDNSFeatureGate: true,
			dnsPolicy:               v1.DNSDefault,
			dnsConfig: &v1.PodDNSConfig{
				Nameservers: []string{"10.0.0.11"},
				Searches:    []string{"my.domain"},
				Options: []v1.PodDNSConfigOption{
					{Name: "ndots", Value: &testNdotsOptionValue},
					{Name: "debug"},
				},
			},
			expectedDNSConfig: &runtimeapi.DNSConfig{
				Servers:  []string{testHostNameserver, "10.0.0.11"},
				Searches: []string{testHostDomain, "my.domain"},
				Options:  []string{"ndots:3", "debug"},
			},
		},
	}

	for _, tc := range testCases {
		if err := utilfeature.DefaultFeatureGate.Set(fmt.Sprintf("CustomPodDNS=%v", tc.customPodDNSFeatureGate)); err != nil {
			t.Errorf("Failed to set CustomPodDNS feature gate: %v", err)
		}

		testPod.Spec.HostNetwork = tc.hostnetwork
		testPod.Spec.DNSConfig = tc.dnsConfig
		testPod.Spec.DNSPolicy = tc.dnsPolicy

		resDNSConfig, err := configurer.GetPodDNS(testPod)
		if err != nil {
			t.Errorf("%s: GetPodDNS(%v), unexpected error: %v", tc.desc, testPod, err)
		}
		if !dnsConfigsAreEqual(resDNSConfig, tc.expectedDNSConfig) {
			t.Errorf("%s: GetPodDNS(%v)=%v, want %v", tc.desc, testPod, resDNSConfig, tc.expectedDNSConfig)
		}
	}
}

func dnsConfigsAreEqual(resConfig, expectedConfig *runtimeapi.DNSConfig) bool {
	if len(resConfig.Servers) != len(expectedConfig.Servers) ||
		len(resConfig.Searches) != len(expectedConfig.Searches) ||
		len(resConfig.Options) != len(expectedConfig.Options) {
		return false
	}
	for i, server := range resConfig.Servers {
		if expectedConfig.Servers[i] != server {
			return false
		}
	}
	for i, search := range resConfig.Searches {
		if expectedConfig.Searches[i] != search {
			return false
		}
	}
	// Options order may be changed after conversion.
	return sets.NewString(resConfig.Options...).Equal(sets.NewString(expectedConfig.Options...))
}

func newTestPods(count int) []*v1.Pod {
	pods := make([]*v1.Pod, count)
	for i := 0; i < count; i++ {
		pods[i] = &v1.Pod{
			Spec: v1.PodSpec{
				HostNetwork: true,
			},
			ObjectMeta: metav1.ObjectMeta{
				UID:  types.UID(10000 + i),
				Name: fmt.Sprintf("pod%d", i),
			},
		}
	}
	return pods
}