etcdserver: forward member promote to leader

etcdserver/server.go

@@ -1635,6 +1635,38 @@ func (s *EtcdServer) RemoveMember(ctx context.Context, id uint64) ([]*membership
 
 // PromoteMember promotes a learner node to a voting node.
 func (s *EtcdServer) PromoteMember(ctx context.Context, id uint64) ([]*membership.Member, error) {
+	resp, err := s.promoteMember(ctx, id)
+	if err != ErrNotLeader {
+		return resp, err
+	}
+
+	cctx, cancel := context.WithTimeout(ctx, s.Cfg.ReqTimeout())
+	defer cancel()
+	// forward to leader
+	for cctx.Err() == nil {
+		leader, err := s.waitLeader(cctx)
+		if err != nil {
+			return nil, err
+		}
+		for _, url := range leader.PeerURLs {
+			resp, err := promoteMemberHTTP(cctx, url, id, s.peerRt)
+			if err == nil {
+				return resp, nil
+			}
+			// If member promotion failed, return early. Otherwise keep retry.
+			if err == membership.ErrIDNotFound || err == membership.ErrLearnerNotReady || err == membership.ErrMemberNotLearner {
+				return nil, err
+			}
+		}
+	}
+
+	if cctx.Err() == context.DeadlineExceeded {
+		return nil, ErrTimeout
+	}
+	return nil, ErrCanceled
+}
+
+func (s *EtcdServer) promoteMember(ctx context.Context, id uint64) ([]*membership.Member, error) {
 	if err := s.checkMembershipOperationPermission(ctx); err != nil {
 		return nil, err
 	}