etcdserver: Fix PeerURL validation

In case of URLs that are synonyms, the current lexicographic sorting
and compare of the URLs fails with frustrating errors. Make sure to do
a full comparison between every set of PeerURLs before failing.

Fixes #11013

etcdserver/api/membership/cluster.go

@@ -759,16 +759,21 @@ func ValidateClusterAndAssignIDs(lg *zap.Logger, local *RaftCluster, existing *R
 	if len(ems) != len(lms) {
 		return fmt.Errorf("member count is unequal")
 	}
-	sort.Sort(MembersByPeerURLs(ems))
-	sort.Sort(MembersByPeerURLs(lms))
 
 	ctx, cancel := context.WithTimeout(context.TODO(), 30*time.Second)
 	defer cancel()
 	for i := range ems {
-		if ok, err := netutil.URLStringsEqual(ctx, lg, ems[i].PeerURLs, lms[i].PeerURLs); !ok {
-			return fmt.Errorf("unmatched member while checking PeerURLs (%v)", err)
+		var err error
+		ok := false
+		for j := range lms {
+			if ok, err = netutil.URLStringsEqual(ctx, lg, ems[i].PeerURLs, lms[j].PeerURLs); ok {
+				lms[j].ID = ems[i].ID
+				break
+			}
+		}
+		if !ok {
+			return fmt.Errorf("PeerURLs: no match found for existing member (%v, %v), last resolver error (%v)", ems[i].ID, ems[i].PeerURLs, err)
 		}
-		lms[i].ID = ems[i].ID
 	}
 	local.members = make(map[types.ID]*Member)
 	for _, m := range lms {