Add proxy mode.

server/join_command.go

@@ -1,9 +1,9 @@
 package server
 
 import (
+	"bytes"
 	"encoding/binary"
 
-	etcdErr "github.com/coreos/etcd/error"
 	"github.com/coreos/etcd/log"
 	"github.com/coreos/etcd/third_party/github.com/coreos/raft"
 )
@@ -40,25 +40,30 @@ func (c *JoinCommand) CommandName() string {
 func (c *JoinCommand) Apply(context raft.Context) (interface{}, error) {
 	ps, _ := context.Server().Context().(*PeerServer)
 
+	var buf bytes.Buffer
 	b := make([]byte, 8)
-	binary.PutUvarint(b, context.CommitIndex())
+	n := binary.PutUvarint(b, context.CommitIndex())
+	buf.Write(b[:n])
 
 	// Make sure we're not getting a cached value from the registry.
 	ps.registry.Invalidate(c.Name)
 
 	// Check if the join command is from a previous peer, who lost all its previous log.
 	if _, ok := ps.registry.ClientURL(c.Name); ok {
-		return b, nil
+		binary.Write(&buf, binary.BigEndian, uint8(0)) // Mark as peer.
+		return buf.Bytes(), nil
 	}
 
 	// Check peer number in the cluster
-	if ps.registry.Count() == ps.Config.MaxClusterSize {
-		log.Debug("Reject join request from ", c.Name)
-		return []byte{0}, etcdErr.NewError(etcdErr.EcodeNoMorePeer, "", context.CommitIndex())
+	if ps.registry.PeerCount() >= ps.ClusterConfig().ActiveSize {
+		log.Debug("Join as proxy ", c.Name)
+		ps.registry.RegisterProxy(c.Name, c.RaftURL, c.EtcdURL)
+		binary.Write(&buf, binary.BigEndian, uint8(1)) // Mark as proxy.
+		return buf.Bytes(), nil
 	}
 
 	// Add to shared peer registry.
-	ps.registry.Register(c.Name, c.RaftURL, c.EtcdURL)
+	ps.registry.RegisterPeer(c.Name, c.RaftURL, c.EtcdURL)
 
 	// Add peer in raft
 	err := context.Server().AddPeer(c.Name, "")
@@ -69,7 +74,8 @@ func (c *JoinCommand) Apply(context raft.Context) (interface{}, error) {
 		ps.followersStats.Followers[c.Name].Latency.Minimum = 1 << 63
 	}
 
-	return b, err
+	binary.Write(&buf, binary.BigEndian, uint8(0)) // Mark as peer.
+	return buf.Bytes(), err
 }
 
 func (c *JoinCommand) NodeName() string {