Merge pull request #35246 from bowei/kubedns-logging

Automatic merge from submit-queue

Refactor some functions in kube-dns to reduce surface area

- Moves federation query path out to its own method
- Creates dns/util and moves some trivial methods to that package

This is just moving of code.

pkg/dns/dns.go

@@ -19,7 +19,6 @@ package dns
 import (
 	"encoding/json"
 	"fmt"
-	"hash/fnv"
 	"net"
 	"strings"
 	"sync"
@@ -33,6 +32,7 @@ import (
 	"k8s.io/kubernetes/pkg/api/unversioned"
 	kcache "k8s.io/kubernetes/pkg/client/cache"
 	clientset "k8s.io/kubernetes/pkg/client/clientset_generated/internalclientset"
+	"k8s.io/kubernetes/pkg/dns/util"
 	"k8s.io/kubernetes/pkg/runtime"
 	"k8s.io/kubernetes/pkg/util/validation"
 	"k8s.io/kubernetes/pkg/util/wait"
@@ -50,9 +50,6 @@ const (
 	// A subdomain added to the user specified dmoain for all pods.
 	podSubdomain = "pod"
 
-	// arpaSuffix is the standard suffix for PTR IP reverse lookups.
-	arpaSuffix = ".in-addr.arpa."
-
 	// Resync period for the kube controller loop.
 	resyncPeriod = 5 * time.Minute
 
@@ -62,15 +59,6 @@ const (
 	// never change. So we expire the cache and retrieve a node once every 180 seconds.
 	// The value is chosen to be neither too long nor too short.
 	nodeCacheTTL = 180 * time.Second
-
-	// default priority used for service records
-	defaultPriority = 10
-
-	// default weight used for service records
-	defaultWeight = 10
-
-	// default TTL used for service records
-	defaultTTL = 30
 )
 
 type KubeDNS struct {
@@ -142,7 +130,7 @@ func NewKubeDNS(client clientset.Interface, domain string, federations map[strin
 		nodesStore:          kcache.NewStore(kcache.MetaNamespaceKeyFunc),
 		reverseRecordMap:    make(map[string]*skymsg.Service),
 		clusterIPServiceMap: make(map[string]*kapi.Service),
-		domainPath:          reverseArray(strings.Split(strings.TrimRight(domain, "."), ".")),
+		domainPath:          util.ReverseArray(strings.Split(strings.TrimRight(domain, "."), ".")),
 		federations:         federations,
 	}
 	kd.setEndpointsStore()
@@ -329,12 +317,12 @@ func (kd *KubeDNS) getServiceFromEndpoints(e *kapi.Endpoints) (*kapi.Service, er
 // elements rooted at the given service, ending at a service record.
 func (kd *KubeDNS) fqdn(service *kapi.Service, subpaths ...string) string {
 	domainLabels := append(append(kd.domainPath, serviceSubdomain, service.Namespace, service.Name), subpaths...)
-	return dns.Fqdn(strings.Join(reverseArray(domainLabels), "."))
+	return dns.Fqdn(strings.Join(util.ReverseArray(domainLabels), "."))
 }
 
 func (kd *KubeDNS) newPortalService(service *kapi.Service) {
 	subCache := NewTreeCache()
-	recordValue, recordLabel := getSkyMsg(service.Spec.ClusterIP, 0)
+	recordValue, recordLabel := util.GetSkyMsg(service.Spec.ClusterIP, 0)
 	subCache.setEntry(recordLabel, recordValue, kd.fqdn(service, recordLabel))
 
 	// Generate SRV Records
@@ -348,8 +336,8 @@ func (kd *KubeDNS) newPortalService(service *kapi.Service) {
 		}
 	}
 	subCachePath := append(kd.domainPath, serviceSubdomain, service.Namespace)
-	host := kd.getServiceFQDN(service)
+	host := getServiceFQDN(kd.domain, service)
-	reverseRecord, _ := getSkyMsg(host, 0)
+	reverseRecord, _ := util.GetSkyMsg(host, 0)
 
 	kd.cacheLock.Lock()
 	defer kd.cacheLock.Unlock()
@@ -370,7 +358,7 @@ func (kd *KubeDNS) generateRecordsForHeadlessService(e *kapi.Endpoints, svc *kap
 		for subIdx := range e.Subsets[idx].Addresses {
 			address := &e.Subsets[idx].Addresses[subIdx]
 			endpointIP := address.IP
-			recordValue, endpointName := getSkyMsg(endpointIP, 0)
+			recordValue, endpointName := util.GetSkyMsg(endpointIP, 0)
 			if hostLabel, exists := getHostname(address, podHostnames); exists {
 				endpointName = hostLabel
 			}
@@ -422,7 +410,7 @@ func (kd *KubeDNS) generateSRVRecordValue(svc *kapi.Service, portNumber int, lab
 	for _, cNameLabel := range labels {
 		host = cNameLabel + "." + host
 	}
-	recordValue, _ := getSkyMsg(host, portNumber)
+	recordValue, _ := util.GetSkyMsg(host, portNumber)
 	return recordValue
 }
 
@@ -455,7 +443,7 @@ func (kd *KubeDNS) newHeadlessService(service *kapi.Service) error {
 func (kd *KubeDNS) newExternalNameService(service *kapi.Service) {
 	// Create a CNAME record for the service's ExternalName.
 	// TODO: TTL?
-	recordValue, _ := getSkyMsg(service.Spec.ExternalName, 0)
+	recordValue, _ := util.GetSkyMsg(service.Spec.ExternalName, 0)
 	cachePath := append(kd.domainPath, serviceSubdomain, service.Namespace)
 	fqdn := kd.fqdn(service)
 	glog.V(2).Infof("newExternalNameService: storing key %s with value %v as %s under %v", service.Name, recordValue, fqdn, cachePath)
@@ -471,12 +459,15 @@ func (kd *KubeDNS) newExternalNameService(service *kapi.Service) {
 // the subtree matching the name are returned.
 func (kd *KubeDNS) Records(name string, exact bool) (retval []skymsg.Service, err error) {
 	glog.V(2).Infof("Received DNS Request:%s, exact:%v", name, exact)
+
 	trimmed := strings.TrimRight(name, ".")
 	segments := strings.Split(trimmed, ".")
 	isFederationQuery := false
 	federationSegments := []string{}
+
 	if !exact && kd.isFederationQuery(segments) {
-		glog.V(2).Infof("federation service query: Received federation query. Going to try to find local service first")
+		glog.V(2).Infof(
+			"federation service query: Received federation query. Going to try to find local service first")
 		// Try quering the non-federation (local) service first.
 		// Will try the federation one later, if this fails.
 		isFederationQuery = true
@@ -485,18 +476,24 @@ func (kd *KubeDNS) Records(name string, exact bool) (retval []skymsg.Service, er
 		// Federation name is 3rd in the segment (after service name and namespace).
 		segments = append(segments[:2], segments[3:]...)
 	}
-	path := reverseArray(segments)
+
+	path := util.ReverseArray(segments)
 	records, err := kd.getRecordsForPath(path, exact)
+
 	if err != nil {
 		return nil, err
 	}
-	if !isFederationQuery {
+
-		if len(records) > 0 {
+	if isFederationQuery {
-			return records, nil
+		return kd.recordsForFederation(records, path, exact, federationSegments)
-		}
+	} else if len(records) > 0 {
-		return nil, etcd.Error{Code: etcd.ErrorCodeKeyNotFound}
+		return records, nil
 	}
 
+	return nil, etcd.Error{Code: etcd.ErrorCodeKeyNotFound}
+}
+
+func (kd *KubeDNS) recordsForFederation(records []skymsg.Service, path []string, exact bool, federationSegments []string) (retval []skymsg.Service, err error) {
 	// For federation query, verify that the local service has endpoints.
 	validRecord := false
 	for _, val := range records {
@@ -505,7 +502,8 @@ func (kd *KubeDNS) Records(name string, exact bool) (retval []skymsg.Service, er
 		if !kd.isHeadlessServiceRecord(&val) {
 			ok, err := kd.serviceWithClusterIPHasEndpoints(&val)
 			if err != nil {
-				glog.V(2).Infof("federation service query: unexpected error while trying to find if service has endpoint: %v", err)
+				glog.V(2).Infof(
+					"federation service query: unexpected error while trying to find if service has endpoint: %v", err)
 				continue
 			}
 			if !ok {
@@ -516,35 +514,36 @@ func (kd *KubeDNS) Records(name string, exact bool) (retval []skymsg.Service, er
 		validRecord = true
 		break
 	}
+
 	if validRecord {
 		// There is a local service with valid endpoints, return its CNAME.
-		name := strings.Join(reverseArray(path), ".")
+		name := strings.Join(util.ReverseArray(path), ".")
 		// Ensure that this name that we are returning as a CNAME response is a fully qualified
 		// domain name so that the client's resolver library doesn't have to go through its
 		// search list all over again.
 		if !strings.HasSuffix(name, ".") {
 			name = name + "."
 		}
-		glog.Infof("federation service query: Returning CNAME for local service : %s", name)
+		glog.V(2).Infof("federation service query: Returning CNAME for local service : %s", name)
 		return []skymsg.Service{{Host: name}}, nil
 	}
 
 	// If the name query is not an exact query and does not match any records in the local store,
 	// attempt to send a federation redirect (CNAME) response.
 	if !exact {
-		glog.V(2).Infof("federation service query: Did not find a local service. Trying federation redirect (CNAME) response")
+		glog.V(2).Infof(
-		return kd.federationRecords(reverseArray(federationSegments))
+			"federation service query: Did not find a local service. Trying federation redirect (CNAME) response")
+		return kd.federationRecords(util.ReverseArray(federationSegments))
 	}
 
 	return nil, etcd.Error{Code: etcd.ErrorCodeKeyNotFound}
 }
 
 func (kd *KubeDNS) getRecordsForPath(path []string, exact bool) ([]skymsg.Service, error) {
-	retval := []skymsg.Service{}
 	if kd.isPodRecord(path) {
 		ip, err := kd.getPodIP(path)
 		if err == nil {
-			skyMsg, _ := getSkyMsg(ip, 0)
+			skyMsg, _ := util.GetSkyMsg(ip, 0)
 			return []skymsg.Service{*skyMsg}, nil
 		}
 		return nil, err
@@ -569,10 +568,14 @@ func (kd *KubeDNS) getRecordsForPath(path []string, exact bool) ([]skymsg.Servic
 	defer kd.cacheLock.RUnlock()
 	records := kd.cache.getValuesForPathWithWildcards(path...)
 	glog.V(2).Infof("Received %d records for %v from cache", len(records), path)
+
+	retval := []skymsg.Service{}
 	for _, val := range records {
 		retval = append(retval, *val)
 	}
+
 	glog.V(2).Infof("records:%v, retval:%v, path:%v", records, retval, path)
+
 	return retval, nil
 }
 
@@ -619,7 +622,7 @@ func (kd *KubeDNS) ReverseRecord(name string) (*skymsg.Service, error) {
 	glog.V(2).Infof("Received ReverseRecord Request:%s", name)
 
 	// if portalIP is not a valid IP, the reverseRecordMap lookup will fail
-	portalIP, ok := extractIP(name)
+	portalIP, ok := util.ExtractIP(name)
 	if !ok {
 		return nil, fmt.Errorf("does not support reverse lookup for %s", name)
 	}
@@ -633,19 +636,6 @@ func (kd *KubeDNS) ReverseRecord(name string) (*skymsg.Service, error) {
 	return nil, fmt.Errorf("must be exactly one service record")
 }
 
-// extractIP turns a standard PTR reverse record lookup name
-// into an IP address
-func extractIP(reverseName string) (string, bool) {
-	if !strings.HasSuffix(reverseName, arpaSuffix) {
-		return "", false
-	}
-	search := strings.TrimSuffix(reverseName, arpaSuffix)
-
-	// reverse the segments and then combine them
-	segments := reverseArray(strings.Split(search, "."))
-	return strings.Join(segments, "."), true
-}
-
 // e.g {"local", "cluster", "pod", "default", "10-0-0-1"}
 func (kd *KubeDNS) isPodRecord(path []string) bool {
 	if len(path) != len(kd.domainPath)+3 {
@@ -671,32 +661,6 @@ func (kd *KubeDNS) getPodIP(path []string) (string, error) {
 	return "", fmt.Errorf("Invalid IP Address %v", ip)
 }
 
-func hashServiceRecord(msg *skymsg.Service) string {
-	s := fmt.Sprintf("%v", msg)
-	h := fnv.New32a()
-	h.Write([]byte(s))
-	return fmt.Sprintf("%x", h.Sum32())
-}
-
-func newServiceRecord(ip string, port int) *skymsg.Service {
-	return &skymsg.Service{
-		Host:     ip,
-		Port:     port,
-		Priority: defaultPriority,
-		Weight:   defaultWeight,
-		Ttl:      defaultTTL,
-	}
-}
-
-// Returns record in a format that SkyDNS understands.
-// Also return the hash of the record.
-func getSkyMsg(ip string, port int) (*skymsg.Service, string) {
-	msg := newServiceRecord(ip, port)
-	hash := hashServiceRecord(msg)
-	glog.V(2).Infof("DNS Record:%s, hash:%s", fmt.Sprintf("%v", msg), hash)
-	return msg, fmt.Sprintf("%x", hash)
-}
-
 // isFederationQuery checks if the given query `path` matches the federated service query pattern.
 // The conjunction of the following conditions forms the test for the federated service query
 // pattern:
@@ -752,7 +716,7 @@ func (kd *KubeDNS) federationRecords(queryPath []string) ([]skymsg.Service, erro
 	// `queryPath` is a reversed-array of the queried name, reverse it back to make it easy
 	// to follow through this code and reduce confusion. There is no reason for it to be
 	// reversed here.
-	path := reverseArray(queryPath)
+	path := util.ReverseArray(queryPath)
 
 	// Check if the name query matches the federation query pattern.
 	if !kd.isFederationQuery(path) {
@@ -850,14 +814,7 @@ func (kd *KubeDNS) getClusterZoneAndRegion() (string, string, error) {
 	return zone, region, nil
 }
 
-func (kd *KubeDNS) getServiceFQDN(service *kapi.Service) string {
+func getServiceFQDN(domain string, service *kapi.Service) string {
-	return strings.Join([]string{service.Name, service.Namespace, serviceSubdomain, kd.domain}, ".")
+	return strings.Join(
-}
+		[]string{service.Name, service.Namespace, serviceSubdomain, domain}, ".")
-
-func reverseArray(arr []string) []string {
-	for i := 0; i < len(arr)/2; i++ {
-		j := len(arr) - i - 1
-		arr[i], arr[j] = arr[j], arr[i]
-	}
-	return arr
 }

pkg/dns/dns_test.go

@@ -35,6 +35,7 @@ import (
 	"k8s.io/kubernetes/pkg/api/unversioned"
 	"k8s.io/kubernetes/pkg/client/cache"
 	fake "k8s.io/kubernetes/pkg/client/clientset_generated/internalclientset/fake"
+	"k8s.io/kubernetes/pkg/dns/util"
 	"k8s.io/kubernetes/pkg/util/sets"
 )
 
@@ -54,7 +55,7 @@ func newKubeDNS() *KubeDNS {
 		reverseRecordMap:    make(map[string]*skymsg.Service),
 		clusterIPServiceMap: make(map[string]*kapi.Service),
 		cacheLock:           sync.RWMutex{},
-		domainPath:          reverseArray(strings.Split(strings.TrimRight(testDomain, "."), ".")),
+		domainPath:          util.ReverseArray(strings.Split(strings.TrimRight(testDomain, "."), ".")),
 		nodesStore:          cache.NewStore(cache.MetaNamespaceKeyFunc),
 	}
 	return kd
@@ -190,7 +191,9 @@ func TestSkySimpleSRVLookup(t *testing.T) {
 	targets := []string{}
 	for _, eip := range endpointIPs {
 		// A portal service is always created with a port of '0'
-		targets = append(targets, fmt.Sprintf("%v.%v", fmt.Sprintf("%x", hashServiceRecord(newServiceRecord(eip, 0))), name))
+		targets = append(targets,
+			fmt.Sprintf("%x.%v",
+				util.HashServiceRecord(util.NewServiceRecord(eip, 0)), name))
 	}
 	assertSRVRecordsMatchTarget(t, rec, targets...)
 }
@@ -255,7 +258,8 @@ func TestSkyNamedPortSRVLookup(t *testing.T) {
 
 	svcDomain := strings.Join([]string{testService, testNamespace, "svc", testDomain}, ".")
 	assertARecordsMatchIPs(t, extra, eip)
-	assertSRVRecordsMatchTarget(t, rec, fmt.Sprintf("%v.%v", fmt.Sprintf("%x", hashServiceRecord(newServiceRecord(eip, 0))), svcDomain))
+	assertSRVRecordsMatchTarget(
+		t, rec, fmt.Sprintf("%x.%v", util.HashServiceRecord(util.NewServiceRecord(eip, 0)), svcDomain))
 	assertSRVRecordsMatchPort(t, rec, 8081)
 }
 
@@ -667,7 +671,7 @@ func assertDNSForHeadlessService(t *testing.T, kd *KubeDNS, e *kapi.Endpoints) {
 }
 
 func assertDNSForExternalService(t *testing.T, kd *KubeDNS, s *kapi.Service) {
-	records, err := kd.Records(getServiceFQDN(kd, s), false)
+	records, err := kd.Records(getServiceFQDN(kd.domain, s), false)
 	require.NoError(t, err)
 	assert.Equal(t, 1, len(records))
 	assert.Equal(t, testExternalName, records[0].Host)
@@ -700,13 +704,13 @@ func getIPForCName(t *testing.T, kd *KubeDNS, cname string) string {
 }
 
 func assertNoDNSForHeadlessService(t *testing.T, kd *KubeDNS, s *kapi.Service) {
-	records, err := kd.Records(getServiceFQDN(kd, s), false)
+	records, err := kd.Records(getServiceFQDN(kd.domain, s), false)
 	require.Error(t, err)
 	assert.Equal(t, 0, len(records))
 }
 
 func assertNoDNSForExternalService(t *testing.T, kd *KubeDNS, s *kapi.Service) {
-	records, err := kd.Records(getServiceFQDN(kd, s), false)
+	records, err := kd.Records(getServiceFQDN(kd.domain, s), false)
 	require.Error(t, err)
 	assert.Equal(t, 0, len(records))
 }
@@ -715,7 +719,7 @@ func assertSRVForNamedPort(t *testing.T, kd *KubeDNS, s *kapi.Service, portName
 	records, err := kd.Records(getSRVFQDN(kd, s, portName), false)
 	require.NoError(t, err)
 	assert.Equal(t, 1, len(records))
-	assert.Equal(t, getServiceFQDN(kd, s), records[0].Host)
+	assert.Equal(t, getServiceFQDN(kd.domain, s), records[0].Host)
 }
 
 func assertNoSRVForNamedPort(t *testing.T, kd *KubeDNS, s *kapi.Service, portName string) {
@@ -725,7 +729,7 @@ func assertNoSRVForNamedPort(t *testing.T, kd *KubeDNS, s *kapi.Service, portNam
 }
 
 func assertNoDNSForClusterIP(t *testing.T, kd *KubeDNS, s *kapi.Service) {
-	serviceFQDN := getServiceFQDN(kd, s)
+	serviceFQDN := getServiceFQDN(kd.domain, s)
 	queries := getEquivalentQueries(serviceFQDN, s.Namespace)
 	for _, query := range queries {
 		records, err := kd.Records(query, false)
@@ -735,7 +739,7 @@ func assertNoDNSForClusterIP(t *testing.T, kd *KubeDNS, s *kapi.Service) {
 }
 
 func assertDNSForClusterIP(t *testing.T, kd *KubeDNS, s *kapi.Service) {
-	serviceFQDN := getServiceFQDN(kd, s)
+	serviceFQDN := getServiceFQDN(kd.domain, s)
 	queries := getEquivalentQueries(serviceFQDN, s.Namespace)
 	for _, query := range queries {
 		records, err := kd.Records(query, false)
@@ -746,16 +750,16 @@ func assertDNSForClusterIP(t *testing.T, kd *KubeDNS, s *kapi.Service) {
 }
 
 func assertReverseRecord(t *testing.T, kd *KubeDNS, s *kapi.Service) {
-	segments := reverseArray(strings.Split(s.Spec.ClusterIP, "."))
+	segments := util.ReverseArray(strings.Split(s.Spec.ClusterIP, "."))
-	reverseLookup := fmt.Sprintf("%s%s", strings.Join(segments, "."), arpaSuffix)
+	reverseLookup := fmt.Sprintf("%s%s", strings.Join(segments, "."), util.ArpaSuffix)
 	reverseRecord, err := kd.ReverseRecord(reverseLookup)
 	require.NoError(t, err)
-	assert.Equal(t, kd.getServiceFQDN(s), reverseRecord.Host)
+	assert.Equal(t, getServiceFQDN(kd.domain, s), reverseRecord.Host)
 }
 
 func assertNoReverseRecord(t *testing.T, kd *KubeDNS, s *kapi.Service) {
-	segments := reverseArray(strings.Split(s.Spec.ClusterIP, "."))
+	segments := util.ReverseArray(strings.Split(s.Spec.ClusterIP, "."))
-	reverseLookup := fmt.Sprintf("%s%s", strings.Join(segments, "."), arpaSuffix)
+	reverseLookup := fmt.Sprintf("%s%s", strings.Join(segments, "."), util.ArpaSuffix)
 	reverseRecord, err := kd.ReverseRecord(reverseLookup)
 	require.Error(t, err)
 	require.Nil(t, reverseRecord)
@@ -775,10 +779,6 @@ func getFederationServiceFQDN(kd *KubeDNS, s *kapi.Service, federationName strin
 	return fmt.Sprintf("%s.%s.%s.svc.%s", s.Name, s.Namespace, federationName, kd.domain)
 }
 
-func getServiceFQDN(kd *KubeDNS, s *kapi.Service) string {
-	return fmt.Sprintf("%s.%s.svc.%s", s.Name, s.Namespace, kd.domain)
-}
-
 func getEndpointsFQDN(kd *KubeDNS, e *kapi.Endpoints) string {
 	return fmt.Sprintf("%s.%s.svc.%s", e.Name, e.Namespace, kd.domain)
 }

pkg/dns/util/util.go

@@ -0,0 +1,88 @@
+/*
+Copyright 2016 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 util
+
+import (
+	"fmt"
+	"hash/fnv"
+	"strings"
+
+	"github.com/golang/glog"
+	"github.com/skynetservices/skydns/msg"
+)
+
+const (
+	// ArpaSuffix is the standard suffix for PTR IP reverse lookups.
+	ArpaSuffix = ".in-addr.arpa."
+	// defaultPriority used for service records
+	defaultPriority = 10
+	// defaultWeight used for service records
+	defaultWeight = 10
+	// defaultTTL used for service records
+	defaultTTL = 30
+)
+
+// extractIP turns a standard PTR reverse record lookup name
+// into an IP address
+func ExtractIP(reverseName string) (string, bool) {
+	if !strings.HasSuffix(reverseName, ArpaSuffix) {
+		return "", false
+	}
+	search := strings.TrimSuffix(reverseName, ArpaSuffix)
+
+	// reverse the segments and then combine them
+	segments := ReverseArray(strings.Split(search, "."))
+	return strings.Join(segments, "."), true
+}
+
+// ReverseArray reverses an array.
+func ReverseArray(arr []string) []string {
+	for i := 0; i < len(arr)/2; i++ {
+		j := len(arr) - i - 1
+		arr[i], arr[j] = arr[j], arr[i]
+	}
+	return arr
+}
+
+// Returns record in a format that SkyDNS understands.
+// Also return the hash of the record.
+func GetSkyMsg(ip string, port int) (*msg.Service, string) {
+	msg := NewServiceRecord(ip, port)
+	hash := HashServiceRecord(msg)
+	glog.V(2).Infof("DNS Record:%s, hash:%s", fmt.Sprintf("%v", msg), hash)
+	return msg, fmt.Sprintf("%x", hash)
+}
+
+// NewServiceRecord creates a new service DNS message.
+func NewServiceRecord(ip string, port int) *msg.Service {
+	return &msg.Service{
+		Host:     ip,
+		Port:     port,
+		Priority: defaultPriority,
+		Weight:   defaultWeight,
+		Ttl:      defaultTTL,
+	}
+}
+
+// HashServiceRecord hashes the string representation of a DNS
+// message.
+func HashServiceRecord(msg *msg.Service) string {
+	s := fmt.Sprintf("%v", msg)
+	h := fnv.New32a()
+	h.Write([]byte(s))
+	return fmt.Sprintf("%x", h.Sum32())
+}