Allow multipe DNS servers as comma-seperated argument for --dns

Depending on an exact cluster setup multiple dns may make sense.
Comma-seperated lists of DNS server are quite common as DNS servers
are always plain IPs.

pkg/apis/componentconfig/types.go

@@ -239,10 +239,10 @@ type KubeletConfiguration struct {
 	// masterServiceNamespace is The namespace from which the kubernetes
 	// master services should be injected into pods.
 	MasterServiceNamespace string
-	// clusterDNS is the IP address for a cluster DNS server.  If set, kubelet
-	// will configure all containers to use this for DNS resolution in
-	// addition to the host's DNS servers
-	ClusterDNS string
+	// clusterDNS is a list of IP address for a cluster DNS server.  If set,
+	// kubelet will configure all containers to use this for DNS resolution
+	// instead of the host's DNS servers
+	ClusterDNS []string
 	// streamingConnectionIdleTimeout is the maximum time a streaming connection
 	// can be idle before the connection is automatically closed.
 	StreamingConnectionIdleTimeout metav1.Duration

pkg/apis/componentconfig/v1alpha1/types.go

@@ -293,10 +293,10 @@ type KubeletConfiguration struct {
 	// masterServiceNamespace is The namespace from which the kubernetes
 	// master services should be injected into pods.
 	MasterServiceNamespace string `json:"masterServiceNamespace"`
-	// clusterDNS is the IP address for a cluster DNS server.  If set, kubelet
-	// will configure all containers to use this for DNS resolution in
-	// addition to the host's DNS servers
-	ClusterDNS string `json:"clusterDNS"`
+	// clusterDNS is a list of IP address for the cluster DNS server.  If set,
+	// kubelet will configure all containers to use this for DNS resolution
+	// instead of the host's DNS servers
+	ClusterDNS []string `json:"clusterDNS"`
 	// streamingConnectionIdleTimeout is the maximum time a streaming connection
 	// can be idle before the connection is automatically closed.
 	StreamingConnectionIdleTimeout metav1.Duration `json:"streamingConnectionIdleTimeout"`

pkg/apis/componentconfig/v1alpha1/zz_generated.conversion.go

@@ -376,7 +376,7 @@ func autoConvert_v1alpha1_KubeletConfiguration_To_componentconfig_KubeletConfigu
 	}
 	out.ClusterDomain = in.ClusterDomain
 	out.MasterServiceNamespace = in.MasterServiceNamespace
-	out.ClusterDNS = in.ClusterDNS
+	out.ClusterDNS = *(*[]string)(unsafe.Pointer(&in.ClusterDNS))
 	out.StreamingConnectionIdleTimeout = in.StreamingConnectionIdleTimeout
 	out.NodeStatusUpdateFrequency = in.NodeStatusUpdateFrequency
 	out.ImageMinimumGCAge = in.ImageMinimumGCAge
@@ -548,7 +548,7 @@ func autoConvert_componentconfig_KubeletConfiguration_To_v1alpha1_KubeletConfigu
 	}
 	out.ClusterDomain = in.ClusterDomain
 	out.MasterServiceNamespace = in.MasterServiceNamespace
-	out.ClusterDNS = in.ClusterDNS
+	out.ClusterDNS = *(*[]string)(unsafe.Pointer(&in.ClusterDNS))
 	out.StreamingConnectionIdleTimeout = in.StreamingConnectionIdleTimeout
 	out.NodeStatusUpdateFrequency = in.NodeStatusUpdateFrequency
 	out.ImageMinimumGCAge = in.ImageMinimumGCAge

pkg/apis/componentconfig/v1alpha1/zz_generated.deepcopy.go

@@ -219,6 +219,11 @@ func DeepCopy_v1alpha1_KubeletConfiguration(in interface{}, out interface{}, c *
 			*out = new(bool)
 			**out = **in
 		}
+		if in.ClusterDNS != nil {
+			in, out := &in.ClusterDNS, &out.ClusterDNS
+			*out = make([]string, len(*in))
+			copy(*out, *in)
+		}
 		if in.ImageGCHighThresholdPercent != nil {
 			in, out := &in.ImageGCHighThresholdPercent, &out.ImageGCHighThresholdPercent
 			*out = new(int32)

pkg/apis/componentconfig/zz_generated.deepcopy.go

@@ -193,6 +193,11 @@ func DeepCopy_componentconfig_KubeletConfiguration(in interface{}, out interface
 			*out = make([]string, len(*in))
 			copy(*out, *in)
 		}
+		if in.ClusterDNS != nil {
+			in, out := &in.ClusterDNS, &out.ClusterDNS
+			*out = make([]string, len(*in))
+			copy(*out, *in)
+		}
 		if in.RegisterWithTaints != nil {
 			in, out := &in.RegisterWithTaints, &out.RegisterWithTaints
 			*out = make([]api.Taint, len(*in))