join endpoint returns HTTP 301 if necessary

http/service.go

@@ -270,6 +270,18 @@ func (s *Service) handleJoin(w http.ResponseWriter, r *http.Request) {
 	}
 
 	if err := s.store.Join(remoteAddr); err != nil {
+		if err == store.ErrNotLeader {
+			leader := s.store.Peer(s.store.Leader())
+			if leader == "" {
+				http.Error(w, err.Error(), http.StatusServiceUnavailable)
+				return
+			}
+
+			redirect := s.FormRedirect(r, leader)
+			http.Redirect(w, r, redirect, http.StatusMovedPermanently)
+			return
+		}
+
 		b := bytes.NewBufferString(err.Error())
 		w.WriteHeader(http.StatusInternalServerError)
 		w.Write(b.Bytes())

store/store.go

@@ -518,10 +518,16 @@ func (s *Store) UpdateAPIPeers(peers map[string]string) error {
 // respond to Raft communications at that address.
 func (s *Store) Join(addr string) error {
 	s.logger.Printf("received request to join node at %s", addr)
+	if s.raft.State() != raft.Leader {
+		return ErrNotLeader
+	}
 
 	f := s.raft.AddPeer(addr)
-	if f.Error() != nil {
-		return f.Error()
+	if e := f.(raft.Future); e.Error() != nil {
+		if e.Error() == raft.ErrNotLeader {
+			return ErrNotLeader
+		}
+		e.Error()
 	}
 	s.logger.Printf("node at %s joined successfully", addr)
 	return nil