Merge pull request #56013 from xiangpengzhao/kubeadm-dns-ip

Automatic merge from submit-queue (batch tested with PRs 56008, 56013). If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.

KubeletConfiguration.BaseConfig.ClusterDNS defaults to the tenth address of MasterConfiguration.Networking.ServiceSubnet

**What this PR does / why we need it**:
If can get DNS IP from MasterConfiguration.Networking.ServiceSubnet, defaults to it. Otherwise defaults to DefaultClusterDNSIP

**Which issue(s) this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close the issue(s) when PR gets merged)*:
ref: https://github.com/kubernetes/kubeadm/issues/28#issuecomment-345502933

**Special notes for your reviewer**:
/cc @luxas 

**Release note**:

```release-note
NONE
```

cmd/kubeadm/app/apis/kubeadm/v1alpha1/defaults.go

@@ -162,7 +162,12 @@ func SetDefaults_KubeletConfiguration(obj *MasterConfiguration) {
 		obj.KubeletConfiguration.BaseConfig.AllowPrivileged = utilpointer.BoolPtr(true)
 	}
 	if obj.KubeletConfiguration.BaseConfig.ClusterDNS == nil {
-		obj.KubeletConfiguration.BaseConfig.ClusterDNS = []string{DefaultClusterDNSIP}
+		dnsIP, err := constants.GetDNSIP(obj.Networking.ServiceSubnet)
+		if err != nil {
+			obj.KubeletConfiguration.BaseConfig.ClusterDNS = []string{DefaultClusterDNSIP}
+		} else {
+			obj.KubeletConfiguration.BaseConfig.ClusterDNS = []string{dnsIP.String()}
+		}
 	}
 	if obj.KubeletConfiguration.BaseConfig.ClusterDomain == "" {
 		obj.KubeletConfiguration.BaseConfig.ClusterDomain = DefaultServiceDNSDomain

cmd/kubeadm/app/constants/BUILD

@@ -11,6 +11,7 @@ go_library(
     srcs = ["constants.go"],
     importpath = "k8s.io/kubernetes/cmd/kubeadm/app/constants",
     deps = [
+        "//pkg/registry/core/service/ipallocator:go_default_library",
         "//pkg/util/version:go_default_library",
         "//vendor/k8s.io/api/core/v1:go_default_library",
     ],

cmd/kubeadm/app/constants/constants.go

@@ -19,11 +19,13 @@ package constants
 import (
 	"fmt"
 	"io/ioutil"
+	"net"
 	"os"
 	"path/filepath"
 	"time"
 
 	"k8s.io/api/core/v1"
+	"k8s.io/kubernetes/pkg/registry/core/service/ipallocator"
 	"k8s.io/kubernetes/pkg/util/version"
 )
 
@@ -256,3 +258,20 @@ func CreateTempDirForKubeadm(dirName string) (string, error) {
 	}
 	return tempDir, nil
 }
+
+// GetDNSIP returns a dnsIP, which is 10th IP in svcSubnet CIDR range
+func GetDNSIP(svcSubnet string) (net.IP, error) {
+	// Get the service subnet CIDR
+	_, svcSubnetCIDR, err := net.ParseCIDR(svcSubnet)
+	if err != nil {
+		return nil, fmt.Errorf("couldn't parse service subnet CIDR %q: %v", svcSubnet, err)
+	}
+
+	// Selects the 10th IP in service subnet CIDR range as dnsIP
+	dnsIP, err := ipallocator.GetIndexedIP(svcSubnetCIDR, 10)
+	if err != nil {
+		return nil, fmt.Errorf("unable to get tenth IP address from service subnet CIDR %s: %v", svcSubnetCIDR.String(), err)
+	}
+
+	return dnsIP, nil
+}

cmd/kubeadm/app/phases/addons/dns/BUILD

@@ -41,7 +41,6 @@ go_library(
         "//cmd/kubeadm/app/util:go_default_library",
         "//cmd/kubeadm/app/util/apiclient:go_default_library",
         "//pkg/api/legacyscheme:go_default_library",
-        "//pkg/registry/core/service/ipallocator:go_default_library",
         "//pkg/util/version:go_default_library",
         "//vendor/k8s.io/api/apps/v1beta2:go_default_library",
         "//vendor/k8s.io/api/core/v1:go_default_library",

cmd/kubeadm/app/phases/addons/dns/dns.go

@@ -18,7 +18,6 @@ package dns
 
 import (
 	"fmt"
-	"net"
 	"runtime"
 
 	apps "k8s.io/api/apps/v1beta2"
@@ -34,7 +33,6 @@ import (
 	kubeadmutil "k8s.io/kubernetes/cmd/kubeadm/app/util"
 	"k8s.io/kubernetes/cmd/kubeadm/app/util/apiclient"
 	"k8s.io/kubernetes/pkg/api/legacyscheme"
-	"k8s.io/kubernetes/pkg/registry/core/service/ipallocator"
 	"k8s.io/kubernetes/pkg/util/version"
 )
 
@@ -60,7 +58,7 @@ func kubeDNSAddon(cfg *kubeadmapi.MasterConfiguration, client clientset.Interfac
 		return err
 	}
 
-	dnsip, err := GetDNSIP(cfg.Networking.ServiceSubnet)
+	dnsip, err := kubeadmconstants.GetDNSIP(cfg.Networking.ServiceSubnet)
 	if err != nil {
 		return err
 	}
@@ -149,7 +147,7 @@ func coreDNSAddon(cfg *kubeadmapi.MasterConfiguration, client clientset.Interfac
 		return fmt.Errorf("error when parsing CoreDNS configMap template: %v", err)
 	}
 
-	dnsip, err := GetDNSIP(cfg.Networking.ServiceSubnet)
+	dnsip, err := kubeadmconstants.GetDNSIP(cfg.Networking.ServiceSubnet)
 	if err != nil {
 		return err
 	}
@@ -244,21 +242,3 @@ func createDNSService(dnsService *v1.Service, serviceBytes []byte, client client
 	}
 	return nil
 }
-
-// GetDNSIP returns a dnsIP, which is 10th IP in svcSubnet CIDR range
-func GetDNSIP(svcSubnet string) (net.IP, error) {
-
-	// Get the service subnet CIDR
-	_, svcSubnetCIDR, err := net.ParseCIDR(svcSubnet)
-	if err != nil {
-		return nil, fmt.Errorf("couldn't parse service subnet CIDR %q: %v", svcSubnet, err)
-	}
-
-	// Selects the 10th IP in service subnet CIDR range as dnsIP
-	dnsIP, err := ipallocator.GetIndexedIP(svcSubnetCIDR, 10)
-	if err != nil {
-		return nil, fmt.Errorf("unable to get tenth IP address from service subnet CIDR %s: %v", svcSubnetCIDR.String(), err)
-	}
-
-	return dnsIP, nil
-}

cmd/kubeadm/app/phases/addons/dns/dns_test.go

@@ -23,6 +23,7 @@ import (
 	"k8s.io/apimachinery/pkg/runtime"
 	clientsetfake "k8s.io/client-go/kubernetes/fake"
 	core "k8s.io/client-go/testing"
+	kubeadmconstants "k8s.io/kubernetes/cmd/kubeadm/app/constants"
 	kubeadmutil "k8s.io/kubernetes/cmd/kubeadm/app/util"
 	api "k8s.io/kubernetes/pkg/apis/core"
 )
@@ -159,7 +160,7 @@ func TestGetDNSIP(t *testing.T) {
 		},
 	}
 	for _, rt := range tests {
-		dnsIP, err := GetDNSIP(rt.svcSubnet)
+		dnsIP, err := kubeadmconstants.GetDNSIP(rt.svcSubnet)
 		if err != nil {
 			t.Fatalf("couldn't get dnsIP : %v", err)
 		}