Shuffle all the replies, not only the ones from the cache...

nameserver/cache.go

@@ -9,7 +9,6 @@ import (
 	"github.com/miekg/dns"
 	. "github.com/weaveworks/weave/common"
 	"math"
-	"math/rand"
 	"sync"
 	"time"
 )
@@ -43,21 +42,6 @@ const (
 	CacheNoLocalReplies uint8 = 1 << iota // not found in local network (stored in the cache so we skip another local lookup or some time)
 )
 
-// shuffleAnswers reorders answers for very basic load balancing
-func shuffleAnswers(answers []dns.RR) []dns.RR {
-	n := len(answers)
-	if n > 1 {
-		rand.Seed(time.Now().UTC().UnixNano())
-
-		for i := 0; i < n; i++ {
-			r := i + rand.Intn(n-i)
-			answers[r], answers[i] = answers[i], answers[r]
-		}
-	}
-
-	return answers
-}
-
 // a cache entry
 type cacheEntry struct {
 	Status   entryStatus // status of the entry
@@ -124,9 +108,6 @@ func (e *cacheEntry) getReply(request *dns.Msg, maxLen int, now time.Time) (*dns
 	reply.Rcode = e.reply.Rcode
 	reply.Authoritative = true
 
-	// shuffle the values, etc...
-	reply.Answer = shuffleAnswers(reply.Answer)
-
 	return reply, nil
 }
 

nameserver/dns.go

@@ -2,6 +2,8 @@ package nameserver
 
 import (
 	"github.com/miekg/dns"
+	"math/rand"
+	"time"
 )
 
 const (
@@ -86,3 +88,20 @@ func getMaxReplyLen(r *dns.Msg, proto dnsProtocol) int {
 	}
 	return maxLen
 }
+
+
+func init() {
+	rand.Seed(time.Now().UTC().UnixNano())
+}
+
+// shuffleAnswers reorders answers for very basic load balancing
+func shuffleAnswers(answers []dns.RR) []dns.RR {
+	if len(answers) > 1 {
+		for i := range answers {
+			j := rand.Intn(i + 1)
+			answers[i], answers[j] = answers[j], answers[i]
+		}
+	}
+
+	return answers
+}

nameserver/server.go

@@ -283,7 +283,7 @@ func (s *DNSServer) localHandler(proto dnsProtocol, kind string, qtype uint16,
 		Debug.Printf("[dns msgid %d] %s: %+v", r.MsgHdr.Id, kind, q)
 		maxLen := getMaxReplyLen(r, proto)
 
-		// cache a reponse if the cache is enabled, and observe the name/IP
+		// cache a response if the cache is enabled, and observe the name/IP
 		maybeCache := func(m *dns.Msg, ttl int, flags uint8) {
 			if !s.cacheDisabled {
 				s.cache.Put(r, m, ttl, flags)
@@ -311,6 +311,7 @@ func (s *DNSServer) localHandler(proto dnsProtocol, kind string, qtype uint16,
 			if reply != nil {
 				Debug.Printf("[dns msgid %d] Returning reply from cache: %s/%d answers",
 					r.MsgHdr.Id, dns.RcodeToString[reply.MsgHdr.Rcode], len(reply.Answer))
+				reply.Answer = shuffleAnswers(reply.Answer)
 				w.WriteMsg(reply)
 				return
 			}
@@ -333,6 +334,7 @@ func (s *DNSServer) localHandler(proto dnsProtocol, kind string, qtype uint16,
 		} else {
 			m := msgBuilder(r, &q, answers)
 			m.Authoritative = true
+			m.Answer = shuffleAnswers(m.Answer)
 			Debug.Printf("[dns msgid %d] Sending response: %s/%s:%s [code:%s]",
 				m.MsgHdr.Id, dns.TypeToString[q.Qtype], q.Name, answers, dns.RcodeToString[m.Rcode])
 			maybeCache(m, nullTTL, 0)